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Z07 vs ZR1 suspension and downforce

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Old 01-01-2018, 01:25 PM
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Default Z07 vs ZR1 suspension and downforce

I have a order placed for a ZR1 and hopefully it gets allocated. Twofold question. First how does the z07 suspension compare to the ďbase ď ZR1? I owned a 2015 Z06 and found a huge benefit in sport mode with my 2017 Z07. Much stiffer and better for me.

Also an obvious concern is putting those 755 horses to the ground. I know the downforce on the high wing package is much higher than my Z07. How does the low wing car compare.

Tks !
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Old 01-01-2018, 07:33 PM
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Here you go.

Also it’s noteworthy to know the high wing produces up to 950lbs of downforce (not sure at what attack angle vs speed, but may be assume at top speed and an attack angle that doesn’t unsettle/destablize the car).

A good question would be how do the little silly splitter end caps supposed to balance the downforce differential between high and low wings?!?!
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Old 01-02-2018, 11:39 AM
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Originally Posted by Kamran View Post
Here you go.

Also itís noteworthy to know the high wing produces up to 950lbs of downforce (not sure at what attack angle vs speed, but may be assume at top speed and an attack angle that doesnít unsettle/destablize the car).

A good question would be how do the little silly splitter end caps supposed to balance the downforce differential between high and low wings?!?!
And compared to stage 3 that I have?
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Old 01-02-2018, 01:26 PM
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Originally Posted by Bbacon View Post
And compared to stage 3 that I have?
If you know the diff between 2 & 3 that you have, itíd be that diff plus the 70%.

If I was to shoot from the hip and venture a guess, the delta between 2>3 is about 100lbs at top speed. That guess is based on assuming 100lbs of supercharger weight being supported by the ďfrontĒ axle, if the designers intent was to balance front and rear axle loading to near 50/50, with little contribution from front end caps.
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Old 01-02-2018, 04:56 PM
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Originally Posted by Kamran View Post
If you know the diff between 2 & 3 that you have, itíd be that diff plus the 70%.

If I was to shoot from the hip and venture a guess, the delta between 2>3 is about 100lbs at top speed. That guess is based on assuming 100lbs of supercharger weight being supported by the ďfrontĒ axle, if the designers intent was to balance front and rear axle loading to near 50/50, with little contribution from front end caps.
Mike Furman just told me that both base cars have same suspension. That sucks for me
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Old 01-02-2018, 08:35 PM
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Originally Posted by Kamran View Post
If you know the diff between 2 & 3 that you have, itíd be that diff plus the 70%.

If I was to shoot from the hip and venture a guess, the delta between 2>3 is about 100lbs at top speed. That guess is based on assuming 100lbs of supercharger weight being supported by the ďfrontĒ axle, if the designers intent was to balance front and rear axle loading to near 50/50, with little contribution from front end caps.
I'm trying to understand what you're getting at here, but my interpretation of what you're saying doesn't make sense from a handling standpoint. Can you offer a little more detail to see if we're on the same page or not?

Thanks.
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Old 01-03-2018, 05:14 PM
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Originally Posted by Kamran View Post
Iím guessing you are questioning the ďshooting from the hipĒ part, and not the first part...Iíll try to put my scattered brain thoughts down as best as Iím able!

My assumptions (obviously not backed up with data, just my own assumptions):

1- GM strives to tune suspension for the highest aero stage (stage 3 aero), so individual models (Z06, GS, ZR1) would result for the quickest lap time during media tests.
2- Once tuning and balancing Stage 3 aero is accomplished, all other lower stages follow suit without further tailor making. They are a close approx, but not as finely balanced for a 50/50.
3- GM strives for a 50/50 front/rear on track balance. This includes various speeds, including initiating corner entries.
4- Iím guessing supercharger weighs roughly 150 lbs, give or take.
5- GS has as close to 50/50 F/R balance ratio as one can get. This one is based on my own GS scaled balancing measurements.
6- Iím assuming out of the 150 lbs supercharger weight, 100 lbs (give or take) is on the front axle, and 50 lbs on rear.
7- considering a GS has a perfect 50/50 balance without the supercharger, a supercharger equipped version requires an extra 100 lbs on the rear to balance out the front, assuming GM seeks the magical 50/50 balance under Stage 3.
8- Iím guessing to create 100 lbs of downforce on the rear, from mid section of Stage 3, you need a bit more in horizontal wind pressure to resist. And looking at the fasteners for the stage 3, based on the fasteners, Iíd be hard pressed assigning much more loading, using standard or appropriate safety factors for design.
9- venturing a guess that a complete Stage 3 (ie Stage 1 + Stage 2 + Stage 3 all summed up) provide about 400 lbs of downforce. Stage 3 is about 1/3 of total, this approx 100 +/- lbs.
10- high wing is at 950 lbs. So Iím guessing low wing produces 500 lbs of downforce (reasonable...may be? Itís much larger than low wing and allows for a more aggressive angle of attack).
11- GM suggest low wing produces 70% more than Stage 2. That puts Stage 2 at 300 lbs. Subtracting 3 - 2, that is 400 (from 9 above) - 300 = 100 lbs.

Above is my random reasoning going at it from various angles for shooting from the hip to come up with 100 lbs. long way of showing they all come to point at approx 100 lbs +/-! In the end, itís not ďmuchĒ larger than 100 and not ďmuchĒ lower than 100 as far as you and I are concerned.

Now if Iím actually wrong by as much as 25%, then Iím off by 25 lbs on the overall downforce! My bad! I.E. kind of an insignificant chump change!
I appreciate your time responding to my question, but respectfully, I can't make sense out of several of your bullet points, particularly numbers 7 and 8 (At the moment I'm reserving saying I disagree with your bullet points).

It appears (to me) you are treating aero downforce on an axle (the rear axle) as being the same as static weight/mass pressing down on the other (ie: front) axle, in an effort to make the F/R tire loads the same. That's the way I'm interpreting it, and I have to disagree if that is your contention.

Not trying to be difficult here, but I can't agree with your conclusion if I'm correctly understanding your reasoning.
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Old 01-03-2018, 09:42 PM
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Originally Posted by Kamran View Post
Fair enough. Itís a round about way of looking at it. Viewing it as a presumption that the more evenly you are loading all ďfourĒ tires going around a track, the better grip (ie faster lap) you have for a road course (excluding straight line drag racing). Idea or goal is as close to evenly distributed tire loads as possible (I fully understand youíll never have this exact condition perfectly). Respectfully, it's not a matter of adding aero to equalize the tire loading. Aero loading and static weight/mass loading are two different animals. In your supercharger weight example (using 150# as a number for calculations) and the wheelbase of a C7 (darn close to 9 feet IIRC), and assuming that the c/g of the supercharger is one foot behind the front axle, then 8/9 of 150# (=133#) sits on the front axle, and 1/9 of 150# (=17#) sits on the rear axle. Because, with the supercharger, you've added 133 pounds (and about as high as possible in the car) of extra work for the front tires, you've increased the understeer tendency of the car. (Adding weight up front and up high is one of the biggest things you DON'T want to do in a sports car.) Now, if you add a big wing to the rear (or a medium wing, or just a big spoiler) you are not doing anything to improve/correct the understeer issue. Additional rear downforce will certainly make the car safer, by reducing/eliminating oversteer, but the rear wing (by itself) will increase the understeer by unloading the front tires. Due to the rear wing position (up high and behind the rear axle), the force vector on the wing tries to make the car do a "wheelie". There's a couple good pictures in one of the road racing threads that illustrate this issue/problem.

None of the individual points above by themselves stand close scrutiny, but my way of approximating via various ďthinkingĒ or ďviewsĒ. In the end, what they tell me is that I donít believe a Stage 3 (1/3 section of rear spoiler) can contribute to more than 100 lbs of downforce (give or take). No matter how you look at it. Thatís my only point.

If you believe the downforce is upwards of 200 or 300 lbs from the mid 24Ē+/- section of Stage 3, Iíd love to hear your views.

Thanks
I can't comment with any specificity on the different stage options as I haven't seen/heard enough about them to accurately compare them. My only point in this post is that a rear wing/spoiler can't bandaid a poor/excessive front weight problem.
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Old 01-04-2018, 10:36 AM
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Originally Posted by Kamran View Post
With all due respect, and I appreciate your inquisitiveness, but you are making a simple shoot from the hip into something scientific and more complicated than even you are willing to share.

If youíd like to discuss the science of suspension, Iíve not seen any ďdynamicĒ mathematical modeling that consider all the factors, such as chassis stiffness, springs, dampers, rolling stiffness, forward stiffness, vertical stiffness, Tire stiffness, rolling alignment changes, etc in conjunction with aero downforce. Iíve seen plenty of mathematical modeling of suspension used by race teams, where several assumptions are made, parameters were estimated and set, and changed by trial and error, until one narrows down the required inputs/parameter to get to a well balanced condition. But all modelings I have seen are based on an instant in travel, I.e. static condition. So an oversimplified static condition is the best I know how to do back of an envelope calculation.

Without trying to turn opís simple question into something that canít be explained in a single ďbookĒ, it seems the only part I see you disagreeing is 100 lbs vs your estimated calculation of 133 lbs. although your calculation would only be accurate if both axles were infinitely stiff, and you are solving the chassis spanning the two axles (without consideration for suspension at each support) as a simply supported beam, then you are close. If we were splitting hair here, Iíd be disagreeing with your 8/9 analysis, since you are not considering relative stiffness of front vs rear suspension (I.e. settlement) which plays a role in load distribution.

I usually like to turn disagreement into something more constructive. Iím willing to learn and I have an open mind, if you are willing to kindly enlighten me. I have learned from you where you disagree. Now Iíd like to listen and learn why and be educated on a better approach on estimating the downforce without having much details, if you are kindly willing to share wisdom. Disagreeing is the easy part...!

As to OPís question, I stand my ground that a 24Ē Stage 3 produces approx 100 lbs of downforce, give or take a few.
I'm not unwilling to share any data, calculations, thoughts, etc. I was just being brief to reduce the tendency of readers to nod off when reading a bunch of minutia.
I enjoy a good technical discussion (I'm a design engineer, and I enjoy learning new things in the discussion process), and I'm trying to keep it respectful. I apologize if it has come off any other way.
I have no disagreements with your assumptions or calculations regarding the downforce capabilities of the different stage configurations. I don't have the detailed info on each stage configuration to do the math or offer up the comparative capabilities.
My main disagreement, as I stated before, is that there is a fundamental difference in handling capability when one axle is loaded with a static load (mass/weight) and the other axle is loaded with aero downforce. You can't bandaid the poor handling end of the car by adding aero downforce to the opposite axle. The force vectors and moment arms will show that.
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Old 01-04-2018, 09:45 PM
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Originally Posted by Kamran View Post
Not at all, Iíve enjoyed chatting with you. Do you think Iím not an engineer? I have no idea.

I think the point you are not seeing, is the importance of corner balancing in motion although adjusted under static conditions. Iím sure you are already aware the extent suspension engineers go to bring a race car to a perfect corner balanced car, most importantly the diagonal load balancing. Why do you think it is important to have all corners of a race car perfectly balanced? Why do you think they introduce an unbalanced cornering when the track favors cornering mostly in one direction. I'm quite familiar with corner balancing (and wedge, when applicable). I'm just not following what this has to do with your initial, basic example of adding 150# to the front end, and adding aero downforce to the rear.

Do you think they go thru all the trouble of corner balancing only to completely ignore the dynamic effects, such as downforce during on track driving and let all comers weights go to hell? The static corner weights don't change during a race (other than due to fuel consumption), while the aero loads change with every mph of speed change.

The more evenly distributed load you have on every tire, while on track, the faster you are. Would you say that the loads are evenly distributed on a Formula 1 car? Unless you are only interested in either braking (you need front tire loads You need 4 tire loads to be competitive. There's a reason why the 911 is so good in braking, because the rear tires are working at a high level in addition to the fronts.), or drag racing (you need rear tire loads).

The point I am making is to keep with the pursuit of balancing weights on tires (which includes downforce), one must first pursue creating equal front to back loading. Again, are the loads on a Formula 1 car equal at the front and rear?

No offense taken. I like disagreements, it makes me think more. What I like more is to learn from the person disagreeing with me, if thereís something they can contribute.

By the way, when you have adjustable suspension, moment arms theory donít mean much. You lower one corner on its suspension, and voila you have less load on that corner and the diagonally opposite corner. Thatís the beauty of suspensions.

Best regards.
As a design engineer, I can't describe how much I disagree with the bolded statement above. There is no shortage of areas on the car where forces are measured (drag, lift, cornering g's, weight/mass, etc), and these forces are directed in a direction and a distance/height (c/g height, wing height, wheelbase length, track width, etc). Whenever you have a force, acting at a distance from a pivot, you have a moment arm. These moment arms are visible any time a car brakes, corners, accelerates, or has a wing placed anywhere on a vehicle. And, these forces and moment arms are there regardless if the car has a suspension, or built like a go-kart.
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Old 01-05-2018, 11:14 AM
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Originally Posted by Kamran View Post
Well I wouldnít worry about anyone reading our posts! By now, we have bored them to death. Iíd be flattering myself, if I were to think people are actually following this thread of conversation...

You are now making the point I was making in post #11, as far as all the variables. Post #11 was kinda long. Which point are you referring to?

Iím quite used to being in an engineering environment, where disagreements are expressed. But most have an idea why, and they share their views, however ďalternative factsĒ they may be. I agree. That's why I'm pointing out where I disagree with you.

Are you now saying tire loads ratios can be all over the place, during a lap on track YES, because a racecar is constantly in a "dynamic" state as it is accelerating, braking, cornering, all while the aero loads vary due to the constantly changing speeds of the car., without regards to inteligentaly and strategically concentrating the loads on specific tire for conditions or corners? FYI, Porscheís are good at take off, due to engine weights being on rear wheels. They donít have any advantage in breaking over an equally equipped car/calipers/rotors. ?? Is it your position that, for equal calipers and rotors, a front heavy car will brake as well as a rear weight biased car?

Iím guessing you may be set to not see the value of balancing weights front/rear & diagonally for the sake of disagreeing. Nonsense. If you wish to insult me, just come out with it. Don't beat around the bush here. I see that in engineering meetings all the time!

The value of balancing and positioning load comes into play whether itís a static condition or a dynamic condition. Again, you are equating static loads (weight/mass) and aero loads (downforce). In a straight line the tires don't see any difference between the two. But in cornering these two forces are night and day different in regards to cornering ability.

The only thing you have so far shared is your analogy of moment arm which doesnít stand a chance in making sense where you have an indeterminate structure. Itís not a simply supported beam on infinitely stiff supports. Simply supported beam analogy is Statics 101, this is beyond that.
Cheers!
Nonsense. We're talking about the forces here (weight and aero), and where those forces interact on the chassis (chassis flex or suspension deflection is minor/irrelevant for this simple thread). These forces, through the different moment arms, change the individual tire loading constantly as the vehicle changes velocity or direction.

How about a simple baseline question: Do you agree or disagree that the forces on each of the tire "treads" changes constantly during the operation of a lap around a road course?
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Old 01-05-2018, 03:28 PM
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Please forgive me for not replying to your post above, because I have not read your reply and at this point will no longer read your posts.
Have a good day sir!

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Old 01-05-2018, 08:20 PM
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Bottom line , it appears to get the z07 equivalent in the zr1you need the entire ZTK package . Big wing in vert looks rediculous
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Old 01-06-2018, 08:33 AM
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Originally Posted by Bbacon View Post
Bottom line , it appears to get the z07 equivalent in the zr1you need the entire ZTK package . Big wing in vert looks rediculous

Wow, I was just looking to figure out differences between Z07 and Base/ZTK ZR1.
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