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Jim, if GM had come to you three years ago and said we want you to design the ultimate track suspension to offer as a special option (think Viper ACR-E destroyer) on the last production year of the C7, what would it be?
You are not limited by NVH, minimum parts life expectancy, etc.....this is the hardcore of track suspension packages that will probably never be offered by a major manufacturer again. This is a car that is designed to be flogged over and over again at track days, etc. Literally a track day special.
You also are allowed an unlimited budget, unlimited track tuning time and extra engineers if needed. I know that last sentence is an engineers wet dream but I'd like get your opinion without corporate limitations.
What changes would you make to the following and anything else you deem necessary for the ultimate showroom track car?
-Springs/spring design...stay leaf spring or go coil over or something else?
-Shocks....electronic or manual adjustment, favorite configuration?
-A-arm bushings or bushing design?
-Stock A-arms or would you design something different?
-Spindles....stay stock, change them or go to a drop spindle?
-Changes in steering rack system?
-Differential...E-diff or something like an OS Giken or Quaife or something else?
-Swaybar and swaybar design options
-Any changes to the tie rod system design or placement?
-Brakes....stay carbon or go steel rotors?
-Favorite tires from the current available options you feel would be great for this setup?
I'm hoping you can answer these questions as it would be interesting to hear your opinions on the ultimate hardcore track package without marketing, accounting or the board of directors getting in the way.
TIA.
Open Checkbook, eh? lol
So this is just off the top of my head. Keeping in mind tires, track width, and cg height, are the 3 most important things. And if it's 3 years ago, I'll assume front front engine configuration. I would kindly ask; no questions about front Vs mid-engine.
-Springs/spring design...stay leaf spring or go coil over or something else?
Even though the tire does not care what spring damper system transfers load to the tire patch, and it's only track based, probably coil overs for the simple reason of the ease to change them for different tracks, i.e.bumpy vs smooth. Also significantly easier to adjust ride height and cross weights.
-Shocks....electronic or manual adjustment, favorite configuration?
For sure MRC. too much felxability and fast program changes.
-A-arm bushings or bushing design?
Heim joints or nylon bushings. Again, ride quality is not a consideration
-Stock A-arms or would you design something different?
the stock arms on the C7 are fine. I would need to look over the kinematics to see if I would re-locate any attachments for better curves. Also the need to obtain 3 to 4 degrees of negative camber.
-Spindles....stay stock, change them or go to a drop spindle?
Assuming I can get the ride height with the spring adjustment, stock. If I can't then I would consider drop spindles, but the lateral stiffness and kinematics would have to be transparent.
-Changes in steering rack system?
No
-Differential...E-diff or something like an OS Giken or Quaife or something else?
ELSD, like the dampers, too much flexability
-Swaybar and swaybar design options
More direct acting bars with the ability to adjust by changing the arm length to the link or on-board adjustment
-Any changes to the tie rod system design or placement?
all heim joints. Rear toe link as well.
-Brakes....stay carbon or go steel rotors?
Carbon for sure. Better pedal feel, output, mass, and lining life
-Favorite tires from the current available options you feel would be great for this setup?
This I would have to investigate. The best slick out there.
Also I'd move the engine rearward, closer to the cg. No interior, custom carbon fiber dash, just large enough to hold the gauges. And a DCT with an optimized automatic mode. Shifting takes time, and an automatic mode is one less of degree of separation for total focus on hitting my marks, both on the track and on the throttle.
That's about all I can think about off the top of my head.
I'll assume front front engine configuration. I would kindly ask; no questions about front Vs mid-engine.
Jim,
First off, thanks so much for what you've done for Corvette over the years, and for communicating with us. My question is one of semantics that I've been taken to task on over the months/years:
Do you consider the C5-C7 (don't remember about the C4) to be a front engine or a front mid-engine setup? Does it make a difference?
First off, thanks so much for what you've done for Corvette over the years, and for communicating with us. My question is one of semantics that I've been taken to task on over the months/years:
Do you consider the C5-C7 (don't remember about the C4) to be a front engine or a front mid-engine setup? Does it make a difference?
Thanks again, and have a good one,
Mike
Hi Mike,
With each new generation, we tried to move the engine in the direction of the CG, but they're pretty much front engine architectures.
I thought Tadge mentioned the 40/60 and it seemed to be a brag not a shortfall! Something about wheels hooking up better...one thing I know is getting C8 Z51 times on par with 750hp plus outgoing C7 ZR1 with only 495 hp speaks volumes of ME over FE and having DCT.
Thanks Jim for your contribution and dedication. To Corvette!!!
If I recall, the reference I made in the podcast was 35/65, and remember I was shooting from the hip during a conversation. I do believe that one or several of the cars were very close to that weight distribution.
I also stated that after evaluation of all those cars, I told Tadge as well as my boss at the time that they were not something to aspire to. We would have to re-invent the wheel, out engineer them. I never said it wasn't possible.
In the Speed Secrets Podcast, I said the engineering team on the C8 was top notch with full capability to achieve the objective. I am certain they have. I have talked with Tadge several times and he is very pleased with the dynamics of the car. I have the utmost respect for him and totally take him at his word.
Now I have to start kissing some butts to get an opportunity to drive one.....
Jim Mero. If and when I get mine, (probably a Z51), and you ever get to St. Louis, you can borrow it any time you want. (Just don't hit anything with it.) I'm thinking realistically I won't see one in my driveway until this time next year.
Thank you for everything you've done for Corvette and for your participation on the CF. It is an honor to hear your opinions on all things sports car.
Cheers, Binger
Last edited by dcbingaman; 07-21-2019 at 08:02 PM.
Given Jim"s dislike of the mid-engine architecture, it is not surprising that he was not that involved in the C8's development.
What really surprises me is his insistence that mid engine cars understeer. I am not aware that he ever states that mid engine cars are typically TUNED to understeer. Instead, it seems that he is stating that understeer is an inherent trait of the mid engine architecture. This is, of course, ridiculous! A mid engine car will always have a tendency to oversteer at the limit since 55% or more of its weight is on the rear wheels.
However, almost all manufacturers compensate for this by tuning their mid engine car's suspension to understeer for safety and liability reasons. And, apparently, GM overcompensated by making the C8 understeer like a pig!
This is just something that we C8 owners will just have to deal with. I, for one, have my solution planned. I am sure that I will be able to get my C8 to handle acceptably with a few weeks worth of work. Unfortunately, we will not be able to rely on GM for solutions since they could be held liable for any unfortunate results of GM's customers modifying their C8s to GM's specifications.
In 2019 it's exhausting to hear anyone say that they weren't aware their controversial comments in a podcast wouldn't be heard by anyone. Really? Negative comments by a former top employee wouldn't generate a viral result? Give us all a break Jim.
You didn't read very carefully. He didn't make negative comments. People who heard his comments interpreted them negatively. Mero can't be held responsible for people who hear what they want to hear, instead of what was said.
Given Jim"s dislike of the mid-engine architecture, it is not surprising that he was not that involved in the C8's development.
What really surprises me is his insistence that mid engine cars understeer. I am not aware that he ever states that mid engine cars are typically TUNED to understeer. Instead, it seems that he is stating that understeer is an inherent trait of the mid engine architecture. This is, of course, ridiculous! A mid engine car will always have a tendency to oversteer at the limit since 55% or more of its weight is on the rear wheels.
However, almost all manufacturers compensate for this by tuning their mid engine car's suspension to understeer for safety and liability reasons. And, apparently, GM overcompensated by making the C8 understeer like a pig!
This is just something that we C8 owners will just have to deal with. I, for one, have my solution planned. I am sure that I will be able to get my C8 to handle acceptably with a few weeks worth of work. Unfortunately, we will not be able to rely on GM for solutions since they could be held liable for any unfortunate results of GM's customers modifying their C8s to GM's specifications.
I don't presume to talk for Jim Mero, but in a sense the data bears out his assertion that its is hard for a mid-engine car on street tires to generate a skidpad centripetal acceleration greater than about 1.1 G's due to understeer. This is because of the asymmetric longitudinal weight distribution (typically 40 / 60) pushes the designer to a large offset in tire size from front to back. This longitudinal distribution allows for both superior "hook-up" in acceleration and in braking, however the two tires most involved in generating the side force on the skidpad are NOT the rear tires, they are the outboard tires, and the weight distribution on the car LEFT-to-RIGHT is 50/50. That means that a mid-engine car has LESS side force capability than a front or rear engine car with a 50/50 distribution simply due to the tire size selections. The tire that "gives out" first is the one with the smallest contact patch - the front one - hence understeer.
If you look at the top 10 "Grip Kings", only ONE of them is a mid-engine, and THAT one is a $1M+ AWD. BTW, Mero's genius is that 5 of the 10 Grip Kings were tuned by HIM. He knows about what he speaks. Now if you are talking race cars, then things change a bit, because race tires provide grip levels well above what a long life, all-weather street tire can manage, (at least for a while). All of those cars are tuned for neutral handling, but as the tires wear, the handling will tend toward understeer "push" or oversteer "loose" and quickly to "undrivable". There is no magic bullet here, physics apply to race cars just as much to street cars.
The optimum arrangement is probably a 50/50 weight distribution with an AWD drivetrain, as exhibited by the fastest sports racing car on the planet, the Porsche 919 Hybrid.
If you look at the top 10 "Grip Kings", only ONE of them is a mid-engine, and THAT one is a $1M+ AWD. BTW, Mero's genius is that 5 of the 10 Grip Kings were tuned by HIM. He knows about what he speaks. Now if you are talking race cars, then things change a bit, because race tires provide grip levels well above what a long life, all-weather street tire can manage, (at least for a while). All of those cars are tuned for neutral handling, but as the tires wear, the handling will tend toward understeer "push" or oversteer "loose" and quickly to "undrivable". There is no magic bullet here, physics apply to race cars just as much to street cars.
The optimum arrangement is probably a 50/50 weight distribution with an AWD drivetrain, as exhibited by the fastest sports racing car on the planet, the Porsche 919 Hybrid.
Poppycock!!!
Number 1 on your list is a rear engine car which has more of its weight on the rear wheels than any mid engine sports car. Also, the fastest cars on the planet are F1 mid engine cars.
I am frankly not entirely sure how to respond to your post since you seem to be confusing so many different factors having to do with suspension tuning. The idea that the load on the front tires is 50/50 from one side to the other is uninformed. What about the effect of weight transfer to the outside tires, or the impact of anti-sway bars?
The fact is that most production mid engine sports cars have their suspensions tuned to excessive underster! This is not something that is inherent in mid engine design. It is just a choice made by many manufacturers for mostly liability reasons. A mid engine car with neutral handling and excellent tires can do well on a skid pad.
There is a reason that almost all racing series are dominated by mid engine cars.
What really surprises me is his insistence that mid engine cars understeer. I am not aware that he ever states that mid engine cars are typically TUNED to understeer. Instead, it seems that he is stating that understeer is an inherent trait of the mid engine architecture. This is, of course, ridiculous! A mid engine car will always have a tendency to oversteer at the limit since 55% or more of its weight is on the rear wheels.
However, almost all manufacturers compensate for this by tuning their mid engine car's suspension to understeer for safety and liability reasons. And, apparently, GM overcompensated by making the C8 understeer like a pig!
This is just something that we C8 owners will just have to deal with. I, for one, have my solution planned. I am sure that I will be able to get my C8 to handle acceptably with a few weeks worth of work. Unfortunately, we will not be able to rely on GM for solutions since they could be held liable for any unfortunate results of GM's customers modifying their C8s to GM's specifications.
Exactly my feeling having had a modified Corvair and worked hard to reduce the inherent Oversteer with it’s 60% rear weight bias! It was a ’67 not to be confused with the swing axle 1960 to 1964! In fact, Ralph Naders, half truth distorted fact book actually used the change in rear suspension to a parallelogram (similar to a Vette) in ’65 and later as “proof” the prior years were a “safety issue.” This is supported by Tadge Juechter’s C8 comments who said the was very concerned about the inherent Oversteer as he came from a Porsche family! He was pleased they were able to eliminate the issue. (see details an quotes below.)
Like yourself I believe GM worked hard to make an inherently Oversteering 60% rear weight car Understeer! Can understand that folks have tested a car GM designed for the average driver who does not know how to deal with an Oversteering car! Have some current thoughts for street driving as to what might be done to promote oversteer but will do more research before my C8 arrives as well as see what some avid trackers find. Bought a 2018 published, very interesting 550 page text book some manufacturers "handling experts" say is the “handling bible.” See below!
SIDEBAR
Porsche’s of the era had the same issue as the Corvair! This was not power induced oversteer, we didn’t have much power in the 1960’s! Some of the Corvair’s Overseeing issue was caused by owner’s (and dealer’s) who didn’t follow GM’s recommendation of 16 psi front tire pressure to reduce front tire traction and promote Understeer! Also if going too fast for a turn the average driver, who was used to Understeer turned the wheel the wrong way. They quickly found themselves looking in the opposite direction! With the simple suspension of the day GM also use rear toe-in to generate a form of rear steer. The toe-in spec was ¼ inch and could range to ~3/8 inches. That is where I had mine set!
Went through several tire brands until I found a Plus 1 solution with 14 inch Continental 714 tires. Car was fun to drive once you learned to deal with the Overrsteer that required the opposite lock to an Understeering car if going too fast for a turn. You only had a split second to react. A normal driver turning the steering wheel the wrong way was quickly off the road- rear first!
From what I researched as to "why no center air dam in my early 2014 Z51." It took ~2 years for Tadge and company to admit it was because the extra front downforce created was promoting some Oversteer and “they require some Understeer” at high speeds! Tadge defined that in a forum post. I’m sure they did not want to give Raplh Nadaer ammunition for another book!
Tadge Juechter Reinforced the Oversteer Issue in Comments!
In a video interview he stated, ”He comes from Porsche family and is well aware of the issues with Oversteer. Keep in mind when of driving age it was in the early 1970’s and the rear heavy Porsche was known for having significant Oversteer. And that wasn’t from Power Oversteer- we didn’t have that much power or turbo’s etc! He said in that interview he was pleased they were able to design around the Oversteer issue!
That was reinforced in an interview published in Super Chevy Magazine, Quoting: “We knew all of the bugaboos that other brands had to discover and correct over a period of many generations. We were always sensitive to the car's rear mass with the mid-engine placement. We had to do it right the first time. There were many little details we had to design into this chassis to correct that, but the driving experience is amazing. “ (He was no doubt referring to Porsche who over many generations was able to get their Oversteering rear heavy cars to be great handling)
MY SCCA Technical Info
It's old and comes from college, many years ago. Recall going to a blackboard drawing optimum cornering paths etc with a friend who built and raced a Lotus Super 7! Have a good friend and neighbor who has restored three old Triumphs, the same model he raced in college and after. He is older than me and was racing in SCCA with Rodger Penske (although a different class!) One is a 98 point car he trailers to Shows!
After looking at my old books, including racing Corvairs I found a newly updated reference some call the handling bible by Professor Guiggiani. It’s a 550 page text book with lots of mathematical equations much like the old Kinematics text I used back when. I like math but no needed to follow the derivations as the graphs and figures made from the theory make it clear! I purchased it and have found it, as did those who reviewed, it to be excellent. Only "digested" the 2 Chapters so far needed to define why some race cars use anti- Akerman. Will be reviewing the other 9 chapters re braking, cornering etc by the time I get my C8!
Given Jim"s dislike of the mid-engine architecture, it is not surprising that he was not that involved in the C8's development.
What really surprises me is his insistence that mid engine cars understeer. I am not aware that he ever states that mid engine cars are typically TUNED to understeer. Instead, it seems that he is stating that understeer is an inherent trait of the mid engine architecture. This is, of course, ridiculous! A mid engine car will always have a tendency to oversteer at the limit since 55% or more of its weight is on the rear wheels.
However, almost all manufacturers compensate for this by tuning their mid engine car's suspension to understeer for safety and liability reasons. And, apparently, GM overcompensated by making the C8 understeer like a pig!
This is just something that we C8 owners will just have to deal with. I, for one, have my solution planned. I am sure that I will be able to get my C8 to handle acceptably with a few weeks worth of work. Unfortunately, we will not be able to rely on GM for solutions since they could be held liable for any unfortunate results of GM's customers modifying their C8s to GM's specifications.
If you are driving a rear mid engine car on a straight road and turn the steering wheel for a turn it will have a tendency to under steer when the wheel is turned. However, throw in some other factors such as lifting off the throttle as the turn is initiated and it will go from under steer to over steer quicker than a front or front mid engine car. My first ride in an old style 911 Porsche was back in 1992 when I rode with my first ever instructor around Watkins Glen in his mid 70s 911. As we came down a hill into a sharp left hander, he stabbed the brake pedal, turned the steering wheel and hit the throttle. The car snapped around the turn. I asked him why he stabbed the brakes like that and was told that transferred weight onto the front wheels so the car would turn when he turned the steering wheel (ie, reducing under steer through an extreme trail braking input). Once it started turning it wanted to over steer and that is why he rolled onto the throttle transferring weight to the rear wheels and thus keeping the rear planted Vs having it kick out in a classic Porsche trailing throttle over steer scenario.
Number 1 on your list is a rear engine car which has more of its weight on the rear wheels than any mid engine sports car. Also, the fastest cars on the planet are F1 mid engine cars.
I am frankly not entirely sure how to respond to your post since you seem to be confusing so many different factors having to do with suspension tuning. The idea that the load on the front tires is 50/50 from one side to the other is uninformed. What about the effect of weight transfer to the outside tires, or the impact of anti-sway bars?
The fact is that most production mid engine sports cars have their suspensions tuned to excessive underster! This is not something that is inherent in mid engine design. It is just a choice made by many manufacturers for mostly liability reasons. A mid engine car with neutral handling and excellent tires can do well on a skid pad.
There is a reason that almost all racing series are dominated by mid engine cars.
yep.. poppycock. Let go of the proof about a STREETCAR in this configuration unless awd and even then you deal with understeer.
Comparing the fastest F1 cars to a streetcar with a center of gravity 4x higher from the ground changes the equation amd diminishes returns from that change of engine placement where 50/50 percent weight distribution is the "secret sauce" the C8 cannot reproduce. There are no 2000lb downforce street cars going 180 around bend... relax molding the situation to fit the "new first ever mid engine corvette!" Great marketing and look at all the buzz for a car that runs around at the same time and speed as a car that released 6yrs ago.. and before you say it won by .9 of second. Put the same 4s on the C7 and what will the difference be?y bet is chevys best vs Mero and Mero beats it hands down.
07-09-2019, 02:39 PM
Exactly my feeling having had a modified Corvair and worked hard to reduce the inherent Oversteer with it’s 60% rear weight bias! It was a ’67 not to be confused with the swing axle 1960 to 1964! In fact, Ralph Naders, half truth distorted fact book actually used the change in rear suspension to a parallelogram (similar to a Vette) in ’65 and later as “proof” the prior years were a “safety issue.” This is supported by Tadge Juechter’s C8 comments who said the was very concerned about the inherent Oversteer as he came from a Porsche family! He was pleased they were able to eliminate the issue. (see details an quotes below.)
