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The picture of the inside wheel of the C8 in a turn scares the hell out of me. Since the C5, Corvette has seen fit to have a negative camber gain from full trounce to full droop. Never seen it before. Also. these cars have eccentric cams to adjust wheel alignment. Bad enough for the Stingray, but for the Z06 and ZR1 is law suit city. Running slicks and high downforce, the damn things will and have failed. I know first hand. Seen all the videos of C7s suddenly swerving to the right and crashing?. A recent video showing a C7 crashing at the ring into the guard rail blames the driver. It is not the driver, it is Tadge.
Poor wheel alignment at the factory and poor geometry is to blame. When you lift your foot off the gas, the e diff opens immediately which may aggravate the situation. I fear the C8 has the same crap going on, although the higher inertia of the rear of the ME car may mitigate a sudden change in direction.
Tadge says only 3 minutes allowed for total wheel alignment. I redesigned my rear suspension and fixed the problem but I dare not show it. Too much of my stuff has been stolen.
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See the daylight under the inside tires above? Much camber thrust is lost.
Mercedes GT has active rear steering so does Porsche 991. Porsche, Ferrari 488 and even the new Supra has multilink geometry. Michelin patented their OPT design which was immediately banned in F1 when Renault tried to use it. Why is this so important? I wouldn't touch this car unless these items of interest have been ot addressed to my satisfaction. A arms are a thing of the past for road cars. Track cars suspension travel is limited and requires fast changes to suit changing conditions. I don't have a clue how to design a ML system.
Michelin OPT system
Mercedes RWS and correct location of upper A arm.
C7 wrong even in the front. Failure. wrong
Looks OK in the front. Severe squat geometry. What will the upper A arm location look like at the back? Will there be rear wheel steering? Take a look at the first picture again.
Last edited by Shaka; 09-20-2018 at 09:04 AM.
Reason: Changes positive to negative in first sentence. Sorry about that.
I have designed suspensions on formula SAE cars, and yes back in the late 90s UTA was one of the top teams. Some of the above suspension designs look wrong. For good positive camber rejection in corners you want the upper a-arm at a downward angle to the upright if the lower a-arm is close to level. This allows for keeping the wheel at the desired angle as the car rolls.
What I don't understand is the negative camber gain in droop at the rear. Watch 0.35 and 0.55 inside wheel in roll. Since the C5, the Corvette engineers have seen fit to have this as part of the loci in the geometry.
Isn't rebound negative camber true for all parallel A-arm systems where the upper A-arm is shorter? Am I missing something?
I have pos camber gain in droop and roll understeer simply by placing my own upper control arm in the optimum location which gives me a 15% lateral gain on inside tire's friction circle.
Much respect! Is your custom upper A-arm longer than the stock one?
My Ferrari F355 has similar camber on the inside rear tire while cornering. In the F355 case, the driver feels the rear end coming around slowly, and as one adds gas, the rear end settles down and one launches themselves out of the corner. This can be used in certain ways to speed up the car--like: a dab on the brakes entering a corner means you don't need to dial in as much steering. It allows one to use more gas to subtract yaw and use less gas to add yaw.
My Ferrari F355 has similar camber on the inside rear tire while cornering. In the F355 case, the driver feels the rear end coming around slowly, and as one adds gas, the rear end settles down and one launches themselves out of the corner. This can be used in certain ways to speed up the car--like: a dab on the brakes entering a corner means you don't need to dial in as much steering. It allows one to use more gas to subtract yaw and use less gas to add yaw.
Watch the rear wheels. Nothing like the C8
The geometry is pretty constant from the 355 to the 458. The 488 has multilink. There are limits to what A arms can do but the Italians are pretty much the best at road and race car chassis.
You can limit the travel of the suspension and lower the car. If you don't have an aero package, you will go slower than a fully compliant suspension like Corvettes have. C56&7. The wheels can follow the pot holes but with a lowered car with limited travel coil/overs, the whole car will ride the pot holes. When you lower the car, you change the geometry adversely mainly in the realm of roll steer, bump steer, etc.Heard of drop spindles? You can't lower multilink cars for performance reasons.. For the road, suspensions are optimized for just a short part of that travel especially bump. The camber changes realized in roll, maximises the friction circle force at each corner. The camber of the wheel relative to the road is what is important. If the car doesn't roll, the cambers remain negative at all 4 corners in the case of a Vette or a Ferrari and that can only be achieved with no travel in the suspension. Load is also a function of the grip. Since the load transfer is to the outside wheels, the camber migration is compromised toward the outside wheels. You can't ignore the work done by the inside wheels like Corvette has done. Camber thrust is a function of camber angle. Multilinks can optimise all of the geometry inside and out, braking and acceleration and braking, camber, roll under or over steer and caster trail. All are influenced by the direction of mass acceleration, unlike A arms. A mid engine car loads the tires differently to a FE car and requires different geometry. to make the tires work. As you can see, the camber of the inside rear wheel on that C8 can't work if you understand camber thrust.
Isn't rebound negative camber true for all parallel A-arm systems where the upper A-arm is shorter? Am I missing something?
Much respect! Is your custom upper A-arm longer than the stock one?
My program determines the length and the location to achieve objectives. Many input factors.
Anyway, place a half inch flat thing on the edge of your desk top. Hold a pencil between your fore fingers on each hand. This is your upright. Your hands are the A arms. Place your left wrist on the flat thing. Place your right wrist on the desk top edge so that your palms face each other. Your right hand is the lower control arm, your left hand is the upper. Keep the lower control arm straight and perpendicular to the desk. Shorten your upper control arm and articulate your hands in the motion of a suspension. Reconfigure the upper A arm till you get the desired camber gain.
You want to start at 2' neg camber when your car is parked. Full travel must go from neg. to pos. camber. You don't want what you see in the picture in roll or droop. It is the angle of the wheel to the road that you are designing.
Now remember, there is also caster and ball joint inclination. Have fun.
The video is from a Ferrari made 20 years after the car I referenced.
A arm design hasn't changed much since the 70s. 65 Shelby Cobras were the state of the art for years. A F308, 355 and a 348 are virtually the same. Relationships to roll couples, load paths, binding and stiction are understood more, Advances in materials, including tires and computers has not changed things much. A arms are limited in camber and tow control, especially at the rear. Simple stick axles worked better than IRS designs for years. Porsche tried to make their Weissach axle in their 928 work with compliant bushes with little success. AMG GT controls rear steer with two electric actuators. Porsche bump steering by design is legendary in all their 911s. Check out current Porsche ML designs.
This is an active single arm suspension at each corner which optimizes grip electronically.
A arm design hasn't changed much since the 70s. 65 Shelby Cobras were the state of the art for years. A F308, 355 and a 348 are virtually the same. Relationships to roll couples, load paths, binding and stiction are understood more, Advances in materials, including tires and computers has not changed things much. A arms are limited in camber and tow control, especially at the rear. Simple stick axles worked better than IRS designs for years. Porsche tried to make their Weissach axle in their 928 work with compliant bushes with little success. AMG GT controls rear steer with two electric actuators. Porsche bump steering by design is legendary in all their 911s. Check out current Porsche ML designs.
This is an active single arm suspension at each corner which optimizes grip electronically.
the long lower and upper control arm design of the porsche looks great but I'd worry about the stiffness of the dynamic suspension design as presented. just doesn't look too stiff front to rear.
Your posts are annoying... the C7ZR1 just trounced the Ford GT in the C&D Lightning lap and has set lap records at most every track it's visited. Clearly the car works. I've raced C5s for years and suspension geometry isn't a weak point for these cars.
If you know so much why not write GM's engineers a letter and apply for a job?
Your posts are annoying... the C7ZR1 just trounced the Ford GT in the C&D Lightning lap and has set lap records at most every track it's visited. Clearly the car works. I've raced C5s for years and suspension geometry isn't a weak point for these cars.
If you know so much why not write GM's engineers a letter and apply for a job?
Your kind spoil it for everybody. Corvette had their reasons to have this geometry that no other sports cars have, only Corvettes. Not one. I don't know why they do this and I even see it on the C8. Maybe it's cost. I don't know how much HP you have or whether you have lowered your car or if it has downforce or slicks but you sure don't know too much about chassis design.
These hard points are in the wrong place, unlike what I have done on my highly modified C6Z with 590 HP at the back wheels.
This is correct for a car with no aero package. I dare not lower it even one inch, but you would never know why?
. Check out the pos. camber at the rear of this F70.
This 488 also. mmmmm. Go back and check out that C8 picture again.
Corvettes tend to track way above their weight class. Id suggest the corvette engineers know what they are doing and the proof is in the consistent track results beating the competition.
I have designed suspensions on formula SAE cars, and yes back in the late 90s UTA was one of the top teams. Some of the above suspension designs look wrong. For good positive camber rejection in corners you want the upper a-arm at a downward angle to the upright if the lower a-arm is close to level. This allows for keeping the wheel at the desired angle as the car rolls.
you want the upper a-arm at a downward angle to the upright if the lower a-arm is close to level. This allows for keeping the wheel at the desired angle as the car rolls.
Yes. And excuse me while I state that in different wording. If the upper control arm is shorter than the lover control arm (which is typically the case) and the lower control arm is level at rest (which is typically the case) then you want the inboard mount point of the upper control arm to be lower than the outboard mount point. The upper control arm would angle up as it goes out.
Corvettes tend to track way above their weight class. Id suggest the corvette engineers know what they are doing and the proof is in the consistent track results beating the competition.
Say, oh wise one, you agree with RGregory who states zactly what I have said and yet Corvette engineers have seen fit to do the opposite. There are two virtues for what Corvette has done since the C5, what would those be?
You haven't a clue.
I have designed suspensions on formula SAE cars, and yes back in the late 90s UTA was one of the top teams. Some of the above suspension designs look wrong. For good positive camber rejection in corners you want the upper a-arm at a downward angle to the upright if the lower a-arm is close to level. This allows for keeping the wheel at the desired angle as the car rolls.
Cool. A friend is a Georgia tech grad and consultant to their Formula SAE program.
This is the NOVA University car in South Florida.
Corvette is wasting tons of grip on the inside tires. Some NASCAR teams take a chance during their pit stops and replace two tires instead of four and usually pay the price. Optimizing grip on the inside tire is an important part of the handling equation.. Without the e diff and near race tires on the Vette, the car would be a real hand full to drive. Remove the grannies on modern high performance cars and even more chaos will occur. The left front get massive positive camber. The rear axle is bent to achieve pos. camber and tow out on the left and tow in and neg. camber on the right. We try to achieve that for left to right transitions for road cars. Pos camber left front.
09-19-2018, 05:13 PM
C8 suspension geometry
