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Jedi-Jurist asked: There have been a lot of reports of stock wheels bending on Grand Sports and Z06s here lately, and I've had one of my own front wheels bend on a brand new Grand Sport. In my situation, there was absolutely no damage, scratch or even a mark anywhere - the wheel just went out of round with less than 1000 miles on the car.
Why is this happening, is Chevy aware of this happening on more than an isolated occurrence, and what is being done to remedy the situation? Will you improve the strength of these Chinese-made wheels and offer a recall/replacement?
Tadge answered: Thank you for the question, Jedi-Jurist. And I hope you are enjoying your Grand Sport! Your question raises a number of issues which I will try to address. I would like to start with your comment about “Chinese wheels”. No Grand Sport wheels come from China. In fact, the majority of our wide Corvette wheels (those most susceptible to bending) are produced by a company named Ronal which is based in Switzerland and manufactures wheels here in North America. A couple of our low-volume Z06 wheels do come from China, but regardless of where they are made, all Corvette wheels are built and tested to GM and Corvette specific standards.
Wheel design is very complex and has to balance many attributes. Everyone wants beautiful wheels, but they also have to be stiff for good handling, strong to resist road damage and low weight. Un-sprung mass is the most important mass in the vehicle. You want light wheels because they enable the suspension to keep the wheel tracking the road surface and you want low rotating inertia because it affects how quickly the car can accelerate and brake. High mass wheels not only hurt handling, but they drive additional mass in the rest of the car. When you hit a pothole, high mass wheels generate higher loads into the suspension and body. As wheels get wider to accommodate wider tires, all these challenges are increased. For these reasons we spend a huge amount of engineering resources on optimizing wheels. We design wheels to withstand extreme pothole loads and test them on high speed laboratory equipment that can simulate the entire life-cycle of the vehicle. I have heard from some people that there is a theory that running the car in sport or track can contribute to damaging a wheel. That is not true.
People are often surprised that a wheel can be bent or cracked without any visible damage to the tire or obvious scratches on the wheel. Our tires have very stiff sidewalls for great handling and the ability to drive the car with no tire pressure whatsoever. As a result they can transfer loads to the wheel without being damaged themselves. A frequent sequence of events is that a wheel gets bent by a road hazard but the damage is initially almost undetectable to the driver. Maybe the driver notices a little more vibration, but many times not if the wheel is only slightly out-of-round (just a millimeter or two). A wheel that is not perfectly round puts stress in the rim that varies with every wheel rotation. Over time fatigue cracks can form after thousands or even millions of cycles. The wheel doesn’t look any different but begins to leak air at the rim. Since it is hundreds or thousands of miles after the damaging event, the driver often can’t remember hitting anything that would justify a crack in the wheel. I have actually experienced this myself. Obviously the wheel has to be replaced since there is no way to reliably repair a rim crack. Tires should be inspected carefully after being dismounted. Sometimes there is no damage on the outside but a blister, bulge, tear or crack can be visible on the inside. With safety as the top priority, any defect would justify a tire replacement.
The question postulates a “rash” of wheel failures. Our field data does not suggest a recent significant increase in the wheel damage rate on our cars. There may be more reports of damage than historically, but, between the Z06 and Grand Sport, we are selling lots more wide-wheel cars than we ever have before. More cars on the road means more chance of hitting something in the road.
We do keep a keen eye on what our customers are experiencing in the field. I don’t know where you live, but the roads here in Michigan seem to be getting worse every year. I can promise you we will continuously improve our designs and validation procedures based how the world is changing.
koranke asked: The owners manual states that, for track events, the factory brake fluid needs to be replaced with qualified high performance brake fluid with a dry boiling point greater than 279 Celsius. It also states that one should replace the track brake fluid with factory brake fluid before driving on public roads. Why is this? I read a blog post from someone suggesting that high performance brake fluid absorbs moisture quicker and consequently can lead to increased corrosion in the braking system compared to regular brake fluid, but I've also seen posts from others who use high performance brake fluid for all driving and don't report any issues. What bad things could happen from using high performance brake fluid for daily driving on public roads? Or, is the issue really that any brake fluid, once subjected to a day on the track, needs to be changed as soon as possible, and that there's nothing wrong with using high-performance brake fluid on the street?
Tadge answered: Koranke, your question raises the exact considerations we take into account when making brake fluid recommendations. Placing customer safety as our highest priority, we advise people to replace the brake fluid after a track event and to revert to street fluid for use on the street. Customers vary tremendously in how hard they use brakes... And it is not necessarily correlated to their lap times. Our professional endurance race car drivers are actually relatively easy on brakes. Some customers are very hard on brakes and end up putting lots of heat into the pads, calipers and fluid. When brake fluid boils or comes near the boiling point, it makes it more likely to boil on the next brake application. Since there is no sure-fire way to assess the condition of the fluid after a track event, we have to recommend replacement as the safest possible alternative.
Your question mentions water absorption. While counterintuitive at first, a small amount of water absorption is actually desirable. The water helps activate the corrosion inhibitors in the brake fluids that help keep brake system components chemically stable. And, just like with antifreeze, these inhibitors are gradually depleted in use, which is the primary reason brake fluid needs to be changed. DOT 3/4 glycol-based fluids will absorb water at different rates and, of course, more than a trace of water starts to be a bad thing. Race fluids, by their nature, generally absorb water more quickly than street brake fluids which can dramatically reduce their boiling point, potentially below that of our factory fluid. This reduction can lead to risk of boiling fluid at lower brake energy. So, again with safety in mind, we recommend going back to street fluid for street driving to avoid the water uptake more likely in race fluids.
FYREANT asked: The Corvette is a car that everybody loves to modify in order to customize and tweak certain aspects to their liking. Do aftermarket parts have any influence on Corvette feature and design enhancement for later model years in a generation model run? If so, can you explain the process for how these influences make their way through to model release?
As an example, some folks with 2014's got certain body parts painted to color match their car such as brake light bezels, hood vents, rear lower diffuser, etc. Some of these sometimes later become factory options. If the Corvette team gets influence from this type of owner customization, what does that look like? Does someone on the team see an aftermarket option and bring it to the rest of the team?
Tadge answered: We on the Corvette team spend a lot of time talking to customers. Members of our program team attend roughly 30 events each year. We hear what customers tell us and we see what aftermarket companies offer. Many of us own Corvettes (of all ages) as well so we are keenly aware of what modifications are available in the market. Sometimes the aftermarket companies are quick to jump into a niche that we intentionally or unintentionally leave open. Quite often there are things we can't offer because we just can't make money doing it. Individuals or companies with different cost models fill in those opportunities. We also plan many years in advance and intentionally roll out new customer options or features year by year. We try to slowly increase the complexity and variety of factory build combinations to make sure we can keep our build quality extremely high. The offering of our accent pieces in more that black was always part of the plan, but we intentionally introduced the car with the carbon flash (actual name of the paint color) only for 2014. Since some people jumped on the opportunity to change to a more monochrome look, it appears that we copied the idea. Not true, that was a pretty obvious opportunity as we developed the car.
We also look at the aftermarket to identify trends as they emerge. An example of that might be in wheel finishes. Black wheels and striped wheels started as a very small niche. We elected to introduce the Stingray to the world on black wheels and they really took off. Later we developed the technology to mass-produce factory striped wheels and people love them! Sometimes we are actually in a better position to offer a feature than an aftermarket company. Our performance data recorder is an example of that. The race team and our development guys used expensive systems to do the telemetry and data recording so critical to their work. Customers started to install their own systems in a variety of add-on ways. We decided we could do it in a much more integrated and affordable way.
We are often asked about the quality and performance of aftermarket products. Since there are thousands of products there is simply no way for us to test them all, validate their performance claims and identify which Corvette models they will or won't work for. On rare occasions we do benchmark an aftermarket product to make sure they don't know something we don't. We have validated, for example, that some low restriction air filters are, in fact, lower restriction than our production units. However, they are compromised in other performance areas: Typically, they are worse in filtration of fine particles, won't hold as much dust, won't pass our water ingestion tests or interfere with the signal quality of the MAF (Mass Air Flow) sensor which is critical for proper engine operation. It is things like this that force us to restrict warranty coverage when people modify their cars in certain ways.
FYREANT asked: Many of us have had to have our center console lid/armrest and/or our drivers door panels replaced under warranty due to the foam getting permanent indentation from continued exposure to peoples elbows. These indentations never "heal" after multiple days of not driving the car. I have personally had two center armrest lids and one drivers door panel replaced and mine have become distorted yet again.
The unfortunate thing is that warranty repair replaces these parts with the exact same part number indicating no improvements have been made to the part. As expected these eventually sees the same indentations return after only 5-10,000 miles of driving. Now that a lot of us with 2014's are out of warranty, the continued replacement of these parts gets costly. Has the Corvette team considered improving the underlying padding with stronger density foam that is more resilliant to permanent indentations and shaping? What options do we have rather than continuing to go through groundhog day with the same parts?
Tadge answered: All manufacturers face trade off questions on interior materials. Generally speaking, materials with higher levels of perceived quality also tend to wear faster. Soft, supple leather shows wear faster than highly treated leather and some synthetics have excellent wear qualities but feel cheap to the touch. Padded surfaces are similar: The simplest solution is to make foams very dense and resistant to deformation, but that undermines the luxurious feel of the interior and hard surfaces can even be painful to elbows and knee sides on long drives or track work.
That said, we did recognize this issue some time ago and made an improvement in construction that better adheres the “skin” of the console cover to the foam underneath. It was shown to be much more durable for the exact condition you reference. That change was made in March of this year and all service stock after that date should be of the new construction. Normally for these answers I would give you specific part numbers to look for but since we have a unique number based on the cover material, color and accent stitch, they are too numerous to list completely. Bottom line is that the warranty replacements done after March of this year should be much improved from before.
You ask about door trim also, but our experience is that door trim replacements are orders of magnitude less than console covers. The door trim is already more robust by design. The only “fix” we would have would be to eliminate any pad and use a hard substrate under the cover. We know from other vehicle experience that would result in far more customer complaints than this issue.
Car54 asked: The recent announcement about the availability of improvements in the suspension calibrations for the C7 said this:
"2014-16 Stingray with Z51 features new calibrations in Tour and Sport modes.
2016 Stingray (non-Z51) features new calibrations in Tour, Sport and Track modes.
2015-16 Z06 (non-Z07) features new calibrations in Tour, Sport and Track modes.
2015-16 Z06 with Z07 Performance Package features new calibrations in Tour, Sport and Track modes."
Why was the 2014-2016 Z51 not included in the Track mode updates? The 2017 cars including the GS were not mentioned nor was there a mention about the 2018 cars. Do the 2017-2018 cars including the GS already have the enhanced calibrations or will they be a part of a future update.
Tadge answered: One good thing about this Ask Tadge feature on the Forum is that you don’t just get access to me, but to the whole Corvette team as well as supporting organizations like GM Performance Accessories. Many of you are familiar with Jim Mero, our ride and handling development engineer who developed the calibration upgrade packages being offered through GM Performance Accessories. I asked him to clarify the whole picture in his own words. And here he is:
Before I get into the rollout of the calibration, and the questions asked, some history might be in order in an effort to make a very complicated situation clearer.
I have read through almost all the threads on the Corvette Forum about the MRC aftermarket calibrations. Overwhelming is an understatement. This is a complex situation and deserves a proper answer, which isn’t short.
With Magnetorheological (Magnetic Ride Control/MagneRide/MRC), we continue to learn and improve as we develop our higher performance variants. Over the past year and a half new tools have been created to help us better analyze data recorded on the bench, on the road, and on the track. Utilization of this data analysis was significant during my tuning of the ZR1. While tuning the ZR1 I realized a revolutionary change that not only improved track performance but also ride quality and handling in Tour and Sport. A change so significant I felt obligated to not only roll it into future model years for all MRC Corvettes, but also make it available to all customers already in possession of a 7th generation Corvette with MRC. While I wish we could roll these out immediately for all, it takes a significant amount of work and time to execute each calibration. Tour, Sport, and Track for each Corvette MRC chassis package have their own individual calibrations. None are shared between any 2 variants. All must go the same extensive validation process as a production implementation. All will be part of the 2019 production fitment. Including the ZR1 I revised 21 total new calibrations by September, 2017. The cadence and roll out of the new MRC calibrations for Chevrolet Performance were determined in the order they were completed.
I will try to address/clarify the questions from the “Ask Tadge” post as well as the ones I am already anticipating based on this reply, including the ones that I recently read in forum posts.
Why is there no track calibration offered for Z51?
As I stated above, I needed to release 21 calibrations for the 2019 production fitment which include the Chevrolet Performance upgrades. Time allotment was not conducive for the implementation of a Z51 track calibration. A new Z51 track calibration is on my “things to do” list, but my “task at hand” list is much longer.
If you’re wondering how could the base car plus F55 (MRC) include a new track calibration but not the Z51, the answer is; like the base car, the base + F55 was never intended to be a track car. So the calibration in track mode is really a hybrid between Sport and Track, something like a Super Sport.
Do the 2017-2018 cars including the GS already have the enhanced calibrations or will they be a part of a future update?
Model year 2017 MRC vehicles were the same as 2016 with the exception of the Grand Sports which did reflect a partial representation of the revised tuning philosophy.
Also included for 2017 production was a new Track calibration for Z06/Z07 (minus the temperature compensation as discussed below).
As I stated above, all 21 2019 production including Chevrolet performance calibrations were completed in September, 2017. This was approximately 8 months after the 2018 calibrations were released for production.
When we hit our 2018 production release dates, the progress I made thus far was released for 2018 production in Tour and Sport for: Z51, Grand Sport Base, Grand Sport w/Z07, Z06 Base, and Z06/Z07.
So yes, Chevrolet Performance will be offering new calibrations for all 2017 and 2018 MRC equipped vehicles including Grand Sport, expect to see the remaining models released in Q1 2018.
What about the car needing to sit for 8 to 10 hours after the flash?
The car can be driven immediately after the flash. It does not have to sit at the dealership. The temperature compensation will not be normalized until the vehicle has sat for 8 to 10 hours. Where and when this happens is irrelevant. When the vehicle sits for 8 to 10 hours, the temperature compensation will then be normalized.
Confusion about the cost to the customer.
$350.00 MSRP, which includes the calibration and installation labor.
Confusion about dealer knowledge about the calibrations.
I have contacted the Executive Director of Global Accessories/Perf Variants/Parts & Motorsports. After receiving an overwhelming number of questions and seeing the customer feedback on the dealer experience with these, Chevrolet Performance is providing an updated dealer bulletin as quickly as possible.
Now I will attempt to go through each MRC package and give a short explanation of the benefits included in the Chevrolet Performance offerings. Again, each chassis package and mode has its own individual calibrations. None are shared between any of them.
Tour Mode
Model(s)
2016 to 2018 Base+F55
2014 to 2018 Z51
2017 to 2018 Grand Sport
2017 to 2018 Grand Sport w/Z07
2015 to 2018 Z06
2015 to 2018 Z06w/Z07
For 2018 (except Base+F55) MRC vehicles, please see footnote
Changes
Major Improvements in impact isolation and integration – Impacts are softer, and less harsh. When the vehicle does encounter rough roads, the structural feel is greatly improved.
Major improvements in ride motions at all speeds. Much more balanced and less abrupt. The car is more poised in compression and rebound, resulting in a flatter ride. This is not implying stiffer body motions, but the vehicle exhibits more a more composed ride.
Parking lot and low speed (25mph and less) the ride motions are more compliant and less jarring.
Handling is more responsive and much more precise. The response of the vehicle is more exact reacting to driver steering inputs.
For 2018 vehicles (except Base+F55), some of the final improvements being implemented for the MRC upgrades were part of the 2018 production release. Thus the improvements for 2018 vehicles are also very significant but not quite as dramatic as the 2014 to 2017 packages.
Sport Mode
Model(s)
2016 to 2018 Base+F55
2014 to 2018 Z51
2017 to 2018 Grand Sport
2017 to 2018 Grand Sport w/Z07
2015 to 2018 Z06
2015 to 2018 Z06w/Z07
For 2018 MRC vehicles (except Base+F55), please see footnote
Changes
Sport also has major improvements in Impact isolation and integration. With these new improvements the impact isolation and integration is better than the Tour mode with the original production calibrations. Impacts are softer, and less harsh. When the vehicle does encounter rough roads, the structural feel is greatly improved.
Major improvements in ride motions at all speeds. Much more balanced and less abrupt. The car is more poised in compression and rebound, resulting in a flatter ride. The Sport mode exhibits significantly more body motion control that Tour.
Handling is more responsive and much more precise. The response of the vehicle is more exact responding to the driver steering inputs weather using Sport mode as a daily driver, or carving through a mountain road.
Parking lot and low speed (25mph and less) the ride motions are more compliant and less jarring.
For 2018 vehicles (except Base+F55), some of the final improvements being implemented for the MRC upgrades were part of the 2018 production release. Thus the improvements for 2018 vehicles are also very significant but not quite as dramatic as the 2014 to 2017 packages.
Track Mode
Model(s)
Grand Sport (FE6) and Z06 (FE6)
Changes
The new track mode is better balanced and response to driver inputs are much more linear near and at the limit of adhesion. With the new Track calibration, the redistribution of the damping in the body, wheel, and handling algorithms makes the car more fluid as it is cornered. The rotation of the car is more precise at initial turn in, and maintains its path through the turn. As the driver rolls into the throttle, vehicle heading is better sustained.
The new Track calibrations increases driver confidence. This, coupled with the vehicle being better balanced during the cornering maneuvers resulted in an average of a 1 second lap time improvement over the original calibration.
Revised temperature compensation tables. As the fluid heated up, during long continuous and repeated runs, sometimes over 100 degrees Celsius (212 degrees Fahrenheit), the damping is effected, not only on an absolute basis, but also the front to rear effecting the balance of the car. New temperature compensation tables were developed to make the balance of the car much more consistent regardless of the damper fluid temperature.
Model(s)
Grand Sport w/Z07 and Z06 w/Z07
Changes
Both of these foundation Track calibrations are included in 2017 production.
The foundation calibrations are solid performers as indicated in the Z06 w/Z07 VIR lap times of 1:55.95 on the full course and 2:39.77 on the Grand Course. The lap times for Grand Sport are 1:59 on the Full Course and 2:45 on the Grand Course.
As explained in the Grand Sport FE6 and Z06 FE6 Track mode paragraph, the new temperature compensation tables are now included in these Track calibrations as part of the Chevrolet Performance offerings and 2019 production.
Upon the completion of the track calibrations I rotated several of our track development engineers with different driving styles through the cars. The result is what the best balance is based on each driving style. If more understeer is desired, this can be easily accomplished by purchasing and installing
Front Stabilizer bushings (Z51 w/MRC, Grand Sport non Z07, Z06, Z06/Z07) part number 84402110 (available February 2018)
Rear Stabilizer bushings (Z51 w/MRC and Z06 w/Z07) part number 23305975
The bushings are easy to install and cost about $6.00 each
If even more precision is desired, Chevrolet Performance also offers lower control arms with stiffer bushing.
Well, that’s a long explanation, but it’s a complicated situation which is why we assume the question was over overwhelmingly voted for and asked in the “Ask Tadge” forum.
BlueDevilZ51 asked: Do you recommend 2014-18 C7s use the new Mobil 1 0w40 dexos2 engine oil that has been announced to be the factory oil fill for 2019s. I'd prefer to use one oil instead of having to change from 5w30 to 15w50 for track use. If you don't recommend the earlier C7 using 0w40, why?
Tadge answered: Yes, the new Mobil1 OW40 Dexos 2 oil (Mobil 1 ESP Formula 0W-40) is also the recommended oil for all C7's prior to 2019. This oil was specifically developed to meet all of GM's performance requirements during engine dyno testing, vehicle road testing and performance track testing including the 2014-2018 Corvettes (all models). The Multi-grade Mobil 1 ESP Formula 0W-40 synthetic motor oil has many benefits including exceptional fast oil flow at startup along with low temperature pump-ability and exceptional viscosity/performance characteristics at high-temperature and high-RPM operating conditions. We are still refining our recommendations for the LT5 in the upcoming ZR1, so they may differ.
jgzo6 asked: I have a 17 z06 and live in las vegas. I use chevron and the highest octane I can find is 91at any brand name gas. The local chev dealer told me 91 is fine I have read that the 17 z06 is tuned different than a 15or16 and that's why the owners states 93. I have called GM and was told it will have a slight impact on performance. What I am concerned about is the effect on engine life and no one has answered that question for me .. My z06 is driven on the street only and used for long trips Engine longevity is important to me.
Tadge answered: The tuning change between model years 15/16 and 17 does not affect engine operation during typical street driving. If you are not working the engine hard, there is little to no difference between 91 and 93 octane fuels. Even in high torque/Hp operation, there will only be slight performance degradation and the ECM (engine control module) will protect the engine from damage over the life of the car. The bottom line is that you needn't worry at all about using 91 octane pump fuel.
Maxie2U asked: Since the introduction of the C7 there has been a total of four part numbers for the A8 torque converter: 24264542, 24273061, 24279495, and 24280631 in that order.
Can you explain why there were so many new part numbers released and what changes were made to the TC?
Tadge answered: Thanks for the question, Maxie2U.
While four part numbers since launch may seem like a lot of design changes to a very important part of the car, it is not. The part numbers represent the initial release and 3 subsequent minor design tweaks. We change part numbers virtually every time we make a product change to enable us to track it through our supply, manufacturing and logistics systems. Many components on the car have a much larger design change history than the torque converter. None of these changes affect the customer experience or the performance of the torque converter. All of the part numbers are back-serviceable and fully interchangeable on any 8-speed Corvette with no other hardware, software or calibration changes required. All three changes were made at Manufacturing's request to make the torque converter easier to make. One change was a geometry tweak to the drive plate to improve the way steel chips resulting from machining operations fall away from the part. It essentially makes it easier to keep the assembly free of debris. Another change was to an internal spline on the stator. We added a chamfer or lead-in to help the male and female parts naturally align as the mating pieces come together. The final item is similar in nature. We modified the geometry of an internal seal to let the interfacing component self-align radially as it is assembled.
I'm guessing the concern behind the question is that the performance of the torque converters is different and everyone wants to know if they have or are getting the "best" one. Please let me assure you that from a customer experience point of view, there is absolutely no difference.
skank asked: I've read and observed with great interest the air management advancements of the new ZR1. Could you explain the air flow paths through the new front fascia and how they are designed and engineered to move air through those internal locations. Knowing that you have already developed brake ducts to direct air to the brake discs, would directional(asymmetrical) fan style wheels help in the air flow path? I also noticed that the new ZR1 wheels are asymmetrical and therefore look different from driver side to passenger side. Would four location specific wheels be required to optimize the aero through the wheel cavity area or is it not worth the extra cost to the ZR1 budget?
Tadge answered: The full answer to this question is worthy of an SAE (Society of Automotive Engineers) technical paper. The ZR1 has significantly improved airflow through the fascia to feed the additional radiators. You can tell with just a glance that there is more open area on the front of a ZR1 than a Z06 or Grand Sport. We measure airflow at average track speeds for a full lap. Compared to Z06, airflow through all radiators is increased by 41% by this measure. This is achieved by improving and optimizing the flow paths through the center as well as the outboard openings. We don't use this much open area for all cars since it creates unnecessary drag in cars that don't need that much cooling. If you look at the C7.R race car, you will see a relatively small opening located in the center of the front fascia.
Additional changes include: The horizontal cooler has been relocated from the position in Z06 to optimize flow performance and its venting is integrated to not disrupt the underwing aerodynamic performance. The center flowpath now features a bumper beam with 4 slot openings and ducting to maximize performance and the hood extractor performance is enhanced by including an extraction lip in the hood surface design. The outboard openings share air between the brake duct and outboard coolers. The baffles behind the opening are splitting the flows and are shaped to optimize the flow into both.
ZR1 track brake cooling has been enhanced by directing flow more efficiently to the control arm mounted hardware. The new front duct actually splits air in two directions. The upper path of the duct feeds air to the control arm deflector then to the knuckle deflector and onto the rotor. The lower path of the duct feeds air into the control arm mounted “airbox” and then up another duct on to the rotor. The airbox is also fed by under vehicle airflow with an enhanced underwing. The control arm mounted brake cooling hardware has evolved from the 2014 Z51 cooling kit (which included lower control arm and knuckle deflectors) to the 2017 Z06 track cooling kit (which adds the airbox and attaching upper duct).
In addition to the enhanced brake cooling, the ZR1 features new Carbon Composite Matrix (CCM) front brake rotors that tolerate higher temperatures than before and new, upgraded pads at all 4 corners.
The pictures below illustrate the difference between current production ZR1 and Z06 track brake cooling set ups. The main difference is in the duct that takes air through the front fascia. As we learned how to improve the air management downstream of the fascia duct on the development of the ZR1, we actually pulled those pieces ahead and released them for the 2017 model year Z06.
ZR1 w/track front brake cooling package installed (black arrows indicate flow from front duct, purple arrows indicate flow from underbody)
Z06 w/track front brake cooling package installed (black arrows indicate flow from front duct, purple arrows indicate flow from underbody)
Relative to the part of the question on wheel design…. We have experimented with “impeller wheels” with foil-shaped spokes or other features to promote air flow over the brakes since at least the 4th generation Corvette. You are right that they would require separate tools for wheels on the left and right side of the car, but if they were effective, we would spend the money. The truth is that the air flow in the wheel openings is very turbulent, nothing like the smooth flow over an airplane wing. The forward part of the wheel opening is a low pressure area so airflow is inboard to outboard. At the rear, it is just the opposite. So which flow do you want to promote? It turns out, the best thing we can do is have wheels with large openings to let the flow go where it wants. Casting or forging airfoil shapes is not mass-efficient given the other structural needs of the wheel. As unsprung mass, we put enormous effort into light, stiff wheels that let the brakes breathe.
FYREANT asked: With the C7 ZR1 having 100HP more and 105TQ more, surely this will put additional strain on many of the vehicles components over what was originally designed for the Stingray, and then the Z06. What component upgrades will we see for the transmission and driveline systems to reliably deliver this power on a continual basis?
Have any of the following components been upgraded to accommodate the power increase and if so, can you speak to what extent?
Tadge answered: Honestly FYREANT, it might be easier to make a list of the parts that haven't changed. You are right, adding that much power and torque stresses a lot of the systems you mention and several others you didn't. I will give you some highlights.
The LT5 engine pushes almost a kilogram of super-heated gas through the exhaust pipes every second at full power. The temperature and pressure of the exhaust was actually enough to inflate sections of the exhaust pipe like a water balloon under extensive track testing. We had to upgrade the steel in the system and redesign sections to cope with those stresses. Shields had to be added in strategic locations to insulate things like electrical connectors and half-shaft boots from the extreme temperatures.
We have talked extensively through the media about how the LT5 generates the power it does. The Small Block V8 excels at generating high horsepower reliably out of a very compact package. This is one of the reasons it is a favorite in the tuning industry. We didn't need to do anything to most of the most of the engine components to handle the additional power over the LT4 with the exception of crank bearings. We moved to a tri-metal material that is more robust in high load applications even though that material prohibits us from selling the car in Europe.
The clutch for the manual trans had to be upgraded in-line with the engine's torque increase, roughly 10%.
Extensive testing of the automatic trans revealed no needs for structural improvements. We increased the load capacity of the spider gears in the differential through a different tooth profile. Although fairly expensive, that upgrade is in production on all Corvettes now. Our primary focus was keeping lube temps as low as possible for both the trans and differential.
The half shafts and prop shaft assembly are carry over from Z06. The worst-case loads for these components is not caused by the engine steady-state peak engine torque. The loads that we design to are more abuse load-cases.... Things like shocking the driveline by side-stepping the clutch at wide open throttle (which we do not recommend). Since those loads are based on driveline and chassis component inertia, the abuse load-cases are similar to Z06. Elsewhere in the suspension, we elected to strengthen the rear upper control arm. Although only needed for ZR1 manuals, the mass change was so small we elected to apply the change to all Corvettes.
To assure sufficient fuel flow to the LT5, we had to increase the Fuel tank pump capacity by 20%
Brake pads at all 4 corners were upgrade to a hybrid street/track compound and the front rotors have a premium heat-treat process that makes them more resistant to fade. Cooling was enhanced as I discussed in my last "Ask Tadge" response on air management for the ZR1.
Finally there are a host of small details.... Things like interlocking washers on the wheel bearing to knuckle attachment. Bottom line is we had to test the ZR1 like it was an all-new cars since it pushed the edge of the performance envelope out, way out.
salcolkat asked: GM says the 2019 ZR1 is the loudest production car they have ever made. Can you explain the difference between the exhaust system on the Zr1 vs the ZO6 and the reason it is louder.
Tadge answered: The LT5 engine in the ZR1 produces 105 more horsepower than the LT4 in the Z06. To do that, it uses a larger blower at higher pressures to force a greater volume of air/fuel mixture into the same sized cylinders resulting in a more powerful combustion event. That also means more pressure on the piston and more torque at the crank – higher output. It also means a larger volume of exhaust gas pushed through the tail pipe and muffler. Bottom line is that we start with more acoustical energy with the higher output engine.
Corvette has been a pioneer in active exhaust. We use a variety of strategies to give people options on how aggressive they want their car to sound. For ZR1 we have taken it a step further by adding internal, passive valves (shown below) that effectively act as a continuously variable orifice instead of the fixed perforations that most manufacturers use to muffle sound. We do still add in fixed perforations (on the “Chimney” in the pic below), but they are much smaller than any of the previous C7 muffler tunings. The smaller these fixed perforations are, the more aggressive the car will sound. Why not eliminate them entirely? Because, even in this car, we are still balancing aggressive sound and refinement, or sound quality. The passive valve allows this tuning change to be possible, and allows the ZR1 to sound extremely aggressive. It acts as a type of acoustic by-pass giving the car a tuned straight pipe type of sound. It is very easy for someone to cut the muffler out of a car and just run straight pipes, but that solution can sound coarse and boomy at lower speeds. The passive valve allows us to have a straight pipe-like sound, but then also have a quieter, less aggressive mode as well.
Most Corvettes have electronically controlled valves on two of the four exhaust tips. You can see those on the rear of the car if you look under the fascia. Those are the key components in our sound management strategy. Under light throttle those valves stay closed and force the exhaust gas to take a torturous path through the muffler. This is true for Stealth and Tour Modes in the ZR1. Sport and Track modes have the electronic valves open far more often. Even in these “Quieter” modes (Stealth/Tour) these electronic valves will open around 4000rpm’s for backpressure reasons. We don’t recommend using stealth or tour on the track since it will retain heat in the exhaust system and probably not help with certain track’s sound limits (because the valves will open under full throttle). In the picture below, which shows a portion of the muffler internals, the electronic valve is not seen because it is outside the muffler and resides on the main flow pipe. When the electronic valve is closed, it creates back pressure that forces open the passive valve in the illustration. The exhaust is forced to expand into the chamber created by the muffler can and pass through multiple perforated barriers and out the secondary flow path. So under light throttle and relatively low flow conditions all of the exhaust exits through the center two exhaust tips. As the driver adds more throttle, more gas passes through the passive valve opening it up wider until there is enough throttle for the electronic valve to open.
Once the electronic valve is open, there is minimal back pressure and the passive valve closes. In this case, most of the exhaust will take the path of least resistance and that is straight through the main flow path. Under these conditions almost all the exhaust exits the outboard exhaust tips. This is why you see the outboard tips dirtier than the inboard tips if the car has been used on track or driven hard. The Z06 and other Corvettes with NPP have fixed orifices in the main flow path in place of the passive valve, so even when the electronic valve is open, there is some leakage over to the secondary flow path. On the ZR1 there is minimal leakage and the sound is a tuned straight-pipe…. much like a race car.
The engineers who invented this system have applied for a patent and I fully expect it to be granted.
As in many things in automotive design, there is a lot of technical engineering, but also an element of art. To be honest there is even some trial and error. Tuning exhaust systems is both and art and a science and we are still learning.
skank asked: I'm very interested in the design, fabrication, and quality standards of the interior in the Corvette Line-up. Could you explain the process of utilizing companies such as Draxlmaier, Lear, JMP, Megatech, Magna, and Faurecia as partners in the fabrication of the Corvette interiors including instrument panels, switchgear, door panels, etc. I have debated with other sports car owners(Porsche) that the methodology of fabricating components with accurate tolerances by any of the above companies do not deviate whether manufacturing for Corvette or Porsche or any other high end manufacturer for that matter. The only difference is the material specifications relative to budget. It would be great to hear your perspective on the design and quality standards relative to your competitors.
Tadge answered: The development of cars is a very complex process. Interiors are no exception. It is simultaneously creative and technical and requires great partnerships with supplier companies like the ones you named. Generally speaking, there is a lot of overlap between OEM's and the interior suppliers they use. To describe the process in over-simplified terms: As designers create a "vision" for how a car's interior could look, engineers canvas suppliers for new technology that could delight customers. The interior is a highly constrained environment with many safety, packaging, functionality and legal requirements. The interior also has to maintain perfect harmony with the exterior of the car as I evolves (can't build a car with little windows on the outside but big windows on the inside). Suppliers are engaged as the design evolves to help us work on materials, manufacturability and panel break up. We work intensely on surface feel and appearance and dimensional quality. Remember most cars do not have one interior, they have hundreds depending on color, premium materials (like suede, leather, wood, carbon and metallic accents), and optional content. You mention switchgear which is a huge part of the interior. Those are really electrical components and they are typically supplied by a different group of companies but have to be seamlessly integrated into the rest of the trim.
I don't have specific knowledge about the dimensional tolerance differences demanded by various manufacturers. My opinion is that the interior suppliers do their best for every customer resulting in a kind of "industry standard" of quality at least in dimensional terms. As you say, the actual materials used is a function of the program's budget. In roughly ascending order of cost, interior constructions on mainstream cars start with molded plastic, then painted plastic, then wrapped components. These can be wrapped in vinyl, leather or suede and additional cost is based on sandwiching foam materials under the wrap to give parts a soft feel. Wood (not on Corvette) and metal (typically aluminum or stainless steel) are added as accent pieces. At the top of the price scale is real carbon fiber (there are a lot of carbon-looking applied finishes) which you only see on the most premium vehicles.
ltomn asked: Knowing that there are a few sports car manufacturers that utilize center lock, forged wheels versus conventional, 5 lug nut wheels, please give us the positive, or negative, reasons for using or not using both wheel types? Porsche does have a center lock, forged wheel option on some of their models that are sub 150K. Since Corvette is approaching 150K with the ZR1 would Corvette consider forged, center lock wheels on it, or any of the Corvette models, as a option? Further, since the ZR1 and ZO6 have massive, broad torque bands, and much higher horsepower, would that affect the reasons for using forged wheels in general?
Tadge answered: Thanks for the question, Itomn. We get this question fairly often from people who think it would be cool to mimic the race car execution. As you may be aware, Corvette once had a factory option for an aluminum knock-off wheels back in 1963 on the C2, which was an early variant of the center lock wheels now offered on some of our competitors.
The chief benefit of center lock wheel attachment (vs our 5 lug nut arrangement) is speed and efficiency of a wheel change in the pit lane at a race track. Simply put, with the correct tools, changing a single lug is faster than changing 5. Also handling a single large nut is a lot more manageable than 5 small ones with much less likelihood of losing one. We usually hear that the center lock look is cleaner and transmits the identity of the race car to the street. However, on nearly every other metric important to our customers, center lock attachments come up short vs. the conventional 5 lug. As you can imagine, wheel attachment is one of the most critical aspects of corner assembly design - particularly on a high power, track-capable vehicle - and GM has spent many hours optimizing this joint. From a safety perspective, wheel attachment is one of the most sensitive joints on the car, and yet it must be easily and frequently serviceable (and potentially in remote locations with less-than-ideal tools). As a case in point, to achieve the same robustness of wheel attachment that 5 Corvette wheel lugs are tightened to 100 lb-ft (140 N-m), Porsche requires 444 lb-ft (600 N-m) on their center lug attachments - a torque wrench capable of 444 lb-ft of torque is nearly 4 feet long! Whether at our assembly plant, our dealers, or at home in the garage, a center lock requires specialty tools for removal and installation. Furthermore, depending on the implementation of the center lock attachment, there may actually be a mass increase! Typically, a bolt or stud/nut is still required to hold the rotor in place to the bearing hub, and frequently this also holds an adapter with the threaded nose that the wheel is attached to - which is likely added mass over a conventional attachment. Finally, in the real world of mass-production cars, where environmental factors, build variation and service incompetence can affect customer safety, having 5 lug nuts offers a form of redundancy making the wheel attachment more resistant to those variables.
To the second part of your question relative to forged vs. cast/flow-formed aluminum wheels with respect to power (and wheel attachment) - Regardless of wheel construction (We have both forged and cast/flow-formed - which is a forging-like process for the rim-section of the wheel), the wheel is rigorously designed to survive our high structural and stiffness requirements (inherent with the broad torque and high horsepower you mention) with the lowest mass. The difference in material ( between cast/flow-formed or forged) is really seen in the stress limits (for yield and fatigue) that the wheels are designed to, but both types of wheels could be properly designed to meet the loading pattern caused by center locks. In our case, the wheel design limitation is frequently wheel stiffness, for which both forged and cast/flow-formed aluminum are actually equivalent (same modulus of elasticity), which makes either wheel construction viable for Corvette. In fact, Z51s have forged wheels, while GS, Z06, and ZR1 have cast/flow-formed wheels, all of which had the wheel construction chosen for optimal wheel design, styling, and robustness.
So in summary, it's actually very possible to run a center-lock wheel attachment for either a cast/flow-formed or forged wheel. In the case of Corvette, we are confident that we have chosen (and will continue to choose in the future) the best combination of wheel attachment and wheel construction for Corvette.
racerns asked: It seems that C6 ZR1/Z07 carbon ceramic rear brake rotor, GM OEM part # 22805790 and AC Delco part # 177-1121, is showing out of stock or discontinued throughout the country. Has this part truly been discontinued and if so what options do the owners of these cars that may only be 5 years old have for a compatible rotor? Are the C7 carbon ceramic rotors usable (fit) on the C6 carbon ceramic brake system? I believe the front rotor will, but the rear may be a different size.
Next part of this question has to do with the new C7 ZR1 brake pads. Are they compatible with the C6 carbon ceramic brake rotors?
Tadge answered: The replacement C6 rear ceramic rotor part number is 84488400 and we currently show a small quantity in stock. More have been ordered and we expect to receive those in a few weeks. Although the basic dimensions are similar, they are not identical so you can't replace C6 rotors with the equivalent C7 part.
As to the question about pads, the C7 ZR1 pads are the same size and could be installed on a C6 with ceramic rotors. However, like many of the answers to questions on this forum, changing a single part in a complex system upsets the carefully engineered balance of that system. Firstly, pads deposit material on the rotor as part of the burnishing process. That process sets up the performance of the system for the remainder of the pad's life. Converting from one composition of pad to another would mix those materials in an un-validated way and likely result in highly variable performance. For this reason, we would always recommend keeping the same pad material for a replacement. If you started with fresh rotors, could you upgrade to the C7 ZR1 pads? Yes, but the more aggressive pads would generate more heat in braking events before fading and that heat affects other components. The front rotors have a special heat treat process on the C7 ZR1 which reduces brake temperatures. The C6 ZR1 with conventional CCM rotors could be compromised by that additional heat going into the caliper or wheel bearings, potentially boiling brake fluid or damaging the caliper or bearing. The C7 brake cooling system is designed to dissipate that heat while the C6 system is not. Finally all our chassis controls are calibrated with an assumed frictional performance by the brakes. ABS, traction control and stability systems would all have performance compromises.
village idiot asked: A number of us were wondering why the hard brake pedal mode ("ice mode" as its been called ) is active in PTM, especially sport 2 and race. It seems like it activates when a wheel is suddenly or quickly locked, like it would on ice or other low friction surface. Unfortunately, a wheel locking quickly happens a lot on the track because, generally, one or more tires are unloaded at any given time, plus things like bumps and curbing unload them.
A combination of being unloaded with big brakes and track brake pads seems to engage this "ice mode" on the track, where it's difficult to see the benefit of it. So what is this "ice mode" and why is active in PTM? It seems very dangerous.
Tadge answered: The key to understanding this phenomenon is that a true ‘ice mode’ where specific calibrations are changed due to distinct surface detection doesn’t exist in any way in the ABS control algorithm. We understand the behavior you are describing but it is not a mode detection that can be turned on or off. The calibrations that can cause this long recovery of deceleration are part of the fundamental ABS wheel control calibration. These calibrations are remarkably complex and significantly beneficial in many situations both on and off track and can’t just be shut off in PTM, they are part of the core wheel control function within ABS. If we did not have variable rates of decel recovery the common race track situations you describe such as curb strikes and spike brake applies while cornering would be very poorly controlled.
To achieve the level of performance expected of Corvette the calibrations are quite sensitive. Further, the control is being done based entirely on four wheel speed sensors which are measuring wheels in extremely dynamic situations. Very rarely is any one wheel traveling at the true speed of the car when ABS is needed. Certain very aggressive driving behaviors can cause any number of calibrations that are critical to overall track performance to produce a lag in decel development, eliminating these situations as much as possible is one of the main tasks that require our extensive engineering effort throughout years of vehicle development work.
Given the significant effort put into optimizing these calibrations we have found that in almost all of the cases where this behavior is noticeable to the driver there have been modifications made to the vehicle that effect the ABS calibration. Different tires, brake pads, and suspension components are examples of modifications which can influence this behavior. We try to predict some common changes that an owner might make to a vehicle but we have no way to test every tire on the market or every brake pad and hardware combination. Further, the more we accommodate race tires or brakes the less robust we are to all season tires or lower dust street pads and vice-versa. You would not expect your engine controller to accommodate a new cam shaft or headers without calibration changes so the same logic applies here.
However, if you have changed any of these components you may find that modifying your brake pedal apply to a softer engagement (even very slight changes) can help the system work with your new components. We have many drivers on the team who have never once experienced this situation and turn in exactly the same lap times as those of us who do occasionally find it.
It’s also important to note that this characteristic of ABS control is not unique to Corvette. It can be found in the ABS systems of many suppliers and across most performance oriented cars, particularly those that have had any kind of modifications made to their brakes or suspension systems.
Having watched these discussions for as long as we have been doing chassis controls, we anticipate many great theories on new, easier ways to do this better… but please keep in mind that any new control idea must be able to work in real time. I.e. with no benefit of analysis after the event or knowledge of the next event (event meaning a 20 millisecond departure of a wheel towards lock or similar situation). It also must work with only 4 wheel speeds and none of those speeds will be a perfectly accurate measure of real vehicle speed. It’s a tough task since there are a near infinite number of variables affecting performance and if we optimize around a rare circumstance we will very likely compromise a commonplace event.
Poor-sha asked: The C7 Z06 and the C7 ZR1 both come with secondary brake cooling ducts that the owner's manual states should be installed for track use and should be removed for street use. Additionally, the C7 ZR1 comes with exhaust cooling hardware that attaches to the tunnel plate and the owner's manual also recommends removing after the track event.
What are the risks associated with leaving this equipment in place during street operation?
Tadge answered: The short answer to your question is that cooling air is super-important on the track, and the vehicle's performance depends on it. Off the track, the same parts add no performance, tend to worsen aerodynamic drag and are possibly detrimental to the vehicle's long term durability. Although most Corvette customers avoid gravel, dirt and muddy roads, we still validate the car's durability on those surfaces. The same functionality that directs cool air to vital components on the track directs dirt and debris to those components in less than ideal conditions. Although we don't see a rash of failures if those "track pieces" are left on, we take the conservative position in recommending they be removed to maximize the long term durability of the cars. Chances are you could leave them on for the life of the car and have no issues, but depending on where and how you drive, you might be better off removing them.
skank asked:
First and foremost I think the C7 taillights are a beautiful, geometrically complex, and integrated design that advanced the C7 generations rear fascia design. Observing the contentious hate affair over the loss of the traditional four simple and basic round taillights of the C6 generation I realize there are logical reasons for the C7's new design of its taillights. I've always thought there was a dual fresnel design function to the internal faceting of the taillight binnacles. Since round taillights have a concentric facet configuration internally they can only send light straight out and still retain a symmetric faceted look. All four of the C7's taillights have sloped bottoms and sloped sides to splay light wide and in a downward direction. Can this design send light straight out when the car is in forward motion and can they also send light in a downward direction when put in reverse thereby lighting the roadway for the backup camera? In effect having a dual functioning use and eliminating separate backup lights. Could you also reveal any new lighting functions that these new generations of LED taillights can accomplish?
Tadge answered:
Like many aspects of automotive design, lighting is heavily controlled by government regulations. These regulations vary by market forcing manufacturers to engineer multiple versions of similar lamps to meet them. Light intensity, color, and distribution pattern are carefully controlled to ensure form does not trump function and that all cars have reasonably well-performing lamps with familiar looks to communicate vehicle operation to surrounding cars. Given these constraints, it is remarkable how many different appearances have been created by automotive designers.
Technology has moved quite quickly in lighting to enable performance and appearance impossible just a few vehicle generations ago. Corvette has historically used the 4 round (ish) design theme that evolved from the second through the 6th generation cars. During that period the "light engine" was a simple incandescent bulb. When light is emitted from a single point-source, round, symmetrical lamps make a lot of sense because they are very efficient. LED technology depends on an array of light engines with custom optics optimizing and focusing the light from each light source. Yes, you can arrange the LED's in a circle to mimic an incandescent solution, but that does not take advantage of the technology's capability in either form or function. That is why you see so many variations of light "signatures" on vehicles today.
Your question asks about dual usage of lamp components to enable the back-up function. Legally, those lamps must be white which, with the advent of back up cameras, makes more sense than ever. We use white LED's for that function, but some cars still use incandescent bulbs. We make every attempt to optimize the back up lamps' contribution to the cameras night time performance within the limits of the law. The optics of the tail lamps do spread some light to the area as well, but we are limited in what we can do. You also ask if the tail lamp function can change when reverse vs forward. To do that, we would have to add some mechanism to change the way light is directed. That additional machinery would cost more and weigh more than the simple addition of a lamp that can be turned on or off.
I have been asked many times why we didn't stick to the traditional 4 round tail lamps. We did seriously consider it, but it never looked right on the car with its ultra-modern design language. Not taking advantage of LED's additional capability was another factor. Finally, we had some customer input that Corvette was starting to look behind the times with little design or technology progress from one generation to the next. And when we asked people why they thought that, they pointed at the back of the car and those 4 round lamps.
jvp asked: A few of the very aggressive track dogs here on the forum have seen issues with the transmission fluid in their Z06s and/or ZR1s sometimes venting out and leaking on the ground. This after some particularly warm or fast sessions on the track. Can you explain what's going on with this and is it expected?
Tadge answered: A good question.... We haven't talked about it much since this is a rare circumstance experienced by very few customers. The short answer is, yes, this is expected behavior.
The transmission has evolved to be a nearly closed and sealed system, practically lubed for life with minimal maintenance needs. When the trans is working hard, the internals heat up and the entrapped air and air/lube mixture expands. We have to provide a vent for excess pressure to escape because internal pressure can dislocate or damage seals that are critical to reliable operation (note: the differential has a similar venting system). When you factor in build variation, fill variation and environmental variables it is easy to see why some transmissions will expel small amounts of air/lube through the vent. This is the transmission's way of finding the optimal level given all the variables. The amount of fluid should be small, wetting the outside of the case and maybe some drips. It should not be puddles on the floor - that could mean a leak which is also very rare. Just because there is no expulsion doesn't mean that the fluid fill is perfect.... Although most people will never have to add fluid to their transmissions, the "aggressive track dogs" you describe in the question must monitor and maintain their fluid fills per our owner's manual instructions.
keagan asked: I would like to know what are your thoughts on the outcome of C&D test against the GT2RS. They mentioned the A8 not being very fast and Ive read that the tires for the car tested were fairly used. This is not the Vettes first rodeo like this. The last time we were out of alignment with rear caster. How do you stop these hiccups from getting to the Halo car on the world stage?
Tadge answered: As you know, Corvettes get quite a lot of automotive media attention. It is a broadly available car that serves as a benchmark against which others are measured. The media have challenging schedules to manage, especially with rare cars and fixed publishing deadlines. The Editors have to be quick on their feet to spot story ideas and comparison tests that will spark readers' interest. Corvettes are not advertised much -- our customers are way too savvy to be swayed by a TV or print ad. So we depend on third-party reviews to get the story of the cars out to interested customers. Bottom line is that we like to be included whenever we can and we don't always get a lot of lead time to prep cars. As the story itself references, we were juggling cars for Lightning Lap and this comparo... and that is just Car and Driver. Many other media outlets have been (and are) urgently requesting access to Corvettes and the ZR1 in particular.
Should we have put new tires on the car? Probably. We looked at them and decided they still had sufficient wear left for this test. In addition, we shipped a fresh set to C/D, but the timing didn't work out for them to be installed and tested. Tight deadlines, as I mentioned.
What about the trans? It is true that the response time for a manually commanded shift on our torque-converter 8-speed automatic takes longer than the 7-speed DCT. That is a fair criticism. On the positive side, our trans is generally smoother and more refined in daily driving. These are trade-offs between transmission types. On the track, left to their own shifting intelligence, the transmissions' shift speeds and overall performance are very close between the two.
As for the rest of the article? My take is that it was fair. It was a bit of an apples-to-oranges comparison. Philosophically, the ZR1 is closer to a highly contented 911 Turbo than the GT2 RS. Of the 20-odd 911 models, the RS cars are the most extremely track-oriented. Exotic features like fixed seat backs and water injection (GT2 RS) require unusual accommodation by the owner. For the most part, their only concessions to street driving are legally mandated ones. The car is also expensive, rare and difficult to acquire. As Car and Driver noted about the car, "It is not a daily driver." The ZR1, like all Corvettes, is a well-rounded machine -- capable of incredibly fast laps on the track while remaining perfectly livable on the street. We can't win them all, and as the article said the GT2 RS won a narrow victory this round...
jvp asked: Now that both Motor Trend and Car and Driver have released their late summer performance comparisons, what are your thoughts on how the ZR1 stacked up against the competitors in each case? Any insight you may be able to offer with respect to each outing?
Tadge answered: This is a bit of an open ended question but it is a good follow up to the last AT question. We are always proud to be tested against the best super cars in the world. With many similar comparisons published at this point and more to come it’s clear that most of the automotive media has concluded that Porsches, Ferraris, McLarens and other exotics are the correct competitors for the Corvette and that, on balance, we do very well in this crowd.
The question specifically referenced the Car and Driver Lighting Lap and the Motor Trend Best Driver’s Car competition. These are very different tests on many levels. One of these differences is definitely track to track variation. Cars tend to do the best on the types of tracks where they are developed most. We never knowingly sacrifice performance at one track in favor of another, however, Laguna is not one of our primary tracks so the car may not be optimal there due to its unique pavement conditions. It’s interesting to note that a couple months prior to Motor Trend’s test at Laguna Seca Randy Pobst set a track record in the ZR1 at Road Atlanta and had many good things to say about it’s performance. There was also a recent Automobile Magazine test vs Porsche and McLaren at the Motorsports Park in Kentucky. It was a very hot day and the ZR1 performed very well. The ZR1 is getting a lot of attention and there will be many other tests of the car around the world. Although some reviews are better than others, we are very happy overall with how the car is being assessed by the media.
Back to Lightning Lap and BDC…. Philosophically it seems as though C&D reports descriptively on how a vehicle drives so the reader can understand the experience while MT has their concept of an ideal driver’s car and they rank the vehicles relative to that ideal. While both are valid methods for comparison that difference alone sheds light on why perspectives differ. Of course this is merely speculation based on reading the articles. We don’t have a seat at the table as editors are crafting their approach.
We should comment on some of the specifics in the article and how those are being expanded upon in forum discussions. Motor Trend made a comment that the Chevy team “begged for a morning run in the cool, dense air” and we know that has led to speculation that the ZR1 is not robust to temperature. The truth of the matter is our team was fine running in the afternoon if the other heavy hitters also ran that afternoon. After all, regardless of cooling system performance, physics applies to all cars equally so a comparison with large temperature differences can never be a fair one. Since the other cars were planned for the morning of day 3, we requested similar treatment.
To further directly address the cooling system question, we were able to prove the robustness and performance of the car during our earlier media launch at Road Atlanta. When Randy set the production car track record the ambient temps were in the low 50s. A couple days later Andy Pilgrim ran a similar session with temps in the mid to upper 80s and was within 1mph to Randy at the end of the backstretch. That same afternoon Andy ran a 13 lap session and his top speed only dropped 3 mph from Lap 1 to Lap 13. You can see Andy’s comments on that run in his Automobile article. Further, during Lightning Lap testing C&D was within 2 seconds of Jim Mero’s record setting lap even though temperatures were 40 degrees warmer. This is a remarkable result for any car, let alone with limited laps for the C&D driver to familiarize themselves with the car.
10-18-2017, 09:10 AM
Grand Sport / Z06 Wheels Bending
