whosurdaddy

If our Corvette's have approximately 50/50 weight distribution, like Acura's AMLS P1 entry, why do we always set up with a camber angle that is almost double up front vs rear? It seems this way even when the T1 guys are running the same tire at all 4 corners, though Acura seems to set their car up with visually similar camber angles front vs rear.

I understand that we have front engines, vs the Acura's mid-engine - but why should this matter if weight distribution is 50/50-ish? I also understand that I'm making an absurd comparison - but the point is still valid. For example, common M3 set up seems to be square - and its also a front engine car. Why is this?

StealthLT4

Probably has something to do with suspension geometry and the camber change per degree of body roll.

JiminVirginia

I think it's just a "best practice" that has evolved over time--as people tinker for better turn in and less understeer--plus the fact that there is more adjustment available in front.

whosurdaddy

I was thinking that this might pop up. Could we be making our cars more subject to snap oversteer as a result of using available camber vs a camber angle that makes the car more balanced?

GM spec's require -1 front AND rear......

mikahb

It's a balancing act, and there are people out there who run as much negative camber in the rear of their Vettes as in the front. One place where this hurts is under hard braking when the rear gets light - negative camber reduces the contact patch in the rear and can decrease the effectiveness of the rear tires in slowing the car down. The front does okay because it has so much weight on it. Another place it hurts is when you're trying to put power down exiting a turn - the weight is shifted back, and that inside rear tire ends up with (say) the 3 degrees static camber you put in PLUS whatever angle the car has rolled over. Now it's at 6 or 7 degrees to the racetrack and won't let you put any power down - not to mention increasing the liklihood of getting the car loose on a hard turn-in.

Also, the front and rear of the car are doing different jobs around the track (the front is causing the car to steer, the rear is propelling the car) and all the dynamics around that play into what setup works best. So, perhaps in a constant-speed, steady-state corner, you could assume that a car with 50/50 weight distribution would want a square setup. But, on a racetrack, such situations are extremely rare, and the staggered setup often recommended for Vettes has evolved as a good compromise.

As one who has driven cars with "good" and "bad" camber setups and seen the resultant tire wear, I will say that it's easy to tell if you've got it pretty close to right... Or way wrong!

Just my $0.02 - worth exactly what you paid for it!

JiminVirginia

My impression is that the tendency to snap oversteer is produced by other things--like a stiff rear sway bar--and not camber.

I tried using the stock ride height with modest camber at both ends, and the oversteer was just too much. Recently, I lowered the car again and maxed out camber front and rear. The car handles a lot better. The rear end even feels more planted.

You have to tinker....

AU N EGL

That is ~50/50 WITH DRIVER AND FUEL. not empty.
yes fuel loads decrease as you drive

Speed Direct

Don't forget that an LMP car has an aero balance that is nearly as important (if not more so in certain regimes) as the weight balance. Both will be factors in setup. A Corvette doesn't have near the downforce to deal with and the aero balance isn't as large of a factor as it is on an LMP. Also, don't forget about the relative differences of the two with regard to power, tire width/grip and total weight. Those three will play differently as each number changes.

davidfarmer

Aero, just like Formula One. Those cars get "free" grip (ie grip without the penalty of excess inertia trying to throw them off of the corners).

bottom line, they have much more overall grip, so they can afford more camber to increase cornering without sacrificing straight line acceleration.

95jersey

Every see video's of how much a tire rolls over with stock suspension and bushings. Optimal would be to have equal negative front and rear....BUT when you go to lay down 500hp after you've hit your apex, your rears would go up in smoke or worse cause a snap oversteer due to lack a traction. Once you get through the initial corner and have
unloaded the tire from the more significant G's forces, you want it as flat as possible to lay down all the power we have. A good lap time in a Corvette is primarly based on how much power you can lay down coming out of a turn.

So you make the sacrafice of some overall corner grip to give you the optimal grip for laying down power out of a turn where most of your time is made up. What good is going another 2mph through a turn, if you lose 10mph at the end of the next strait cause you can't put the power down. make sense? Without any true aero, you want whatever set up helps you exit the corner as fast as possible.

davidfarmer

it just came to me that also, I've never had a car that needed as much negative camber in the rear. I think the fact that the rear wheels don't steer simply doesn't load them the same as the fronts.

robvuk

I think you've got the best explanation. I would add that the car is 50/50 and is very balanced in a turn with constant throttle. On throttle and it understeers, off throttle and it oversteers. During a lap you are mostly on or off throttle which in either case, causes the front tires to take most of the cornering abuse. Therefore the added camber is necessary.

Solofast

It is simply a result of the geometry.

Front suspensions of our cars have lot of kingpin angle (angle of a line between the two front ball joints). This kingpin angle results in a loss of front camber as the steering angle increases. As a result of this, you need more static negative camber in the front, because you are losing negative camber up there as the front tire steers.... This is also why autocrossers tend to use more front negative camber than road racers, the speeds are slower and the steering angles are higher, so they need more negative camber to start with.

The rear doesn't steer (much), so all it sees is the effect of body roll, bushing softness and the camber gain or loss from the linkage. As a result you don't need as much to start with.

Some cars (like cars with struts) don't have as high a kingpin angle and as a result don't lose as much negative front camber when turning.

Caster also can mitigate the effect of kingpin angle since as you crank the wheel the caster effectively adds negative camber. Some cars, like BMW's have a low kingpin angle (as a result of having struts) and use a lot of caster. The net effect is that they need less static negative camber in the front.

argonaut

Corner weights of my 99 FRC with full tank and 175 lb driver. Car has a bolt in bar, Corbeau A4s, AC condenser delete, Dewitts radiator (only weight mods of any significance):

LF 907 RF 872
LR 837 RR 811
LF-RR X 1718
LR-RF X 1709
Total 3472

Full tank no driver:
LF 852 RF 859 1711 52.62996001
LR 759 RR 781 1540 47.37003999
LF-RR X 1633
LR-RF X 1618


That doesn't add up to a 50/50 distribution - any thoughts?

thehammer69

My corner weighting was around 52/48 on the front to rear also...

whosurdaddy

Some interesting explanations. I think the most clarifying may be the king ping angle story provided by Solofast. Also, negative influence of negative camber with a high-HP car makes sense.

Thanks.

BrianCunningham

GM dials in a lot of undesteer in their street cars.

Helps keep non-pro drivers pointed in the right direction.

MungoZ06

At the end of the day, aren't good pyrometer metrics (out-mid-in) key to determining optimal camber?

shifter77

Great explanation MIKAHB.
MY guess besides all the all the downforce the ACURA has, they are using the SAME TIRE SIZE front/rear.

whosurdaddy

gives them the ability to rotate tires across all four wheels periodically