Oversteer!

[priapism]

My SE30 was oversteering quite a bit at the last track day we went to. It would push if you went in way hot, but in steady state cornering and coming out of the corner it wanted to swing its tail. I thought the solution to this was to soften up the rear sway, but when I got home I found the rear sway to be on full soft. I don't think it's rollover-oversteer because I just wasn't getting that much body roll. I stiffened the rear bar about an inch to see though.

I'm running about -3* camber in the front. Standard SE30 suspension setup. Car corner balanced slightly front heavy (~720 on front wheels, 620 on rears).

Ideas?

[nrubenstein]

Check your rear toe. It can wander a lot. Mike Trent has developed 3/8ths of rear toe out on his car.

Needless to say, the handling is poor.

[priapism]

Hahaha just took a good long look at your sig pic, hilarious!

[pantelones]

Check rear tire pressure? Is this a new set up or one that you have been running for awhile?

[jlevie]

How much camber on the rear wheels? How much rear toe? A good place to be is 3deg camber and zero toe.

If both front wheels have 720lb and both rears 620lb (I doubt they are that even) you have 53.7% on the front wheels. Which means that the rear wheels are decidedly light and you will have oversteer. Taking weight off the front, if you can, or adding/moving weight to the rear is going to help. You can run thicker spring pads up front and no rear spring pads to shift weight to the rear wheels. Front to rear balance is important, but corner balance is more important. I'd suggest doing what you can to get better balance, but concentrate more on corner balance. Disconnecting the rear sway has a big affect, but I suspect that you will find that the car pushes too much.

Other factors are the condition of the clutches in the differential and rear tire pressures. You can also run thicker spacers on the rear tires than on the fronts. 5-7mm of difference is very noticeable.

A Spec E30 is going to loose on corner exit. There is only so much (given the rules) that one can do. My car has 52% on the front wheels and is only 0.5% off in corner weights. It carries 20lb of ballast that is mounted on the rear bulkhead next to the right rear shock tower. The battery has also been relocated to be next to the right rear shock tower.. The left front and right rear wheels have extra thick spring pads, the right front has skinny pads, and the left rear has none. I have the rear sway set as soft as it will go and I use 12mm rear spacers and 5mm front spaces. The rear alignment is 3deg of camber and zero toe and I run two psi less in the rear tires. The car is still loose on corner exit, but it is manageable and doesn't do anything sudden.

[priapism]

Doesn't lower = lighter? The corner weights were "about" that, I didn't remember the exact numbers. But here they are. I think I'm going to try to eliminate a little weight in the front, but I don't think that's the root of the problem.

Tire pressures were 35 all around. Running Star Specs, not the spec tires.

It wasn't terrible, just...pretty loose. I will have to check toe and camber tonight, but I thought it was at zero. Rear camber isn't adjustable, is it? And I thought toe was only adjustable via ride height?

[VinniE30]

If both front wheels have 720lb and both rears 620lb (I doubt they are that even) you have 53.7% on the front wheels. Which means that the rear wheels are decidedly light and you will have oversteer. Taking weight off the front, if you can, or adding/moving weight to the rear is going to help.

More weight in the rear will create more oversteer. Not the other way around. The more rear weight bias, the more oversteer, and the more front weight bias the more understeer. All else being equal of corse just comparing weight distribution. Think of how 911s with their rear engine and rear weight bias oversteer and audis with their strong front weight bias understeer.

I agree with the part that taking weight off the front will help handling in general, but not for the reason you said, the logic behind it doesn't follow. And adding weight to the rear will definitely not reduce oversteer.

[priapism]

^ we have a minimum weight, so we have to stay above 2700. Being so close, if I take weight from one end, it has to go back in the other.

[cwbaader]

Your cross weights are way off...your rf/lr should be the same weight as the lf/rr. The way you have it the car would push in one direction and be loose in the other. Get them equal and then worry about push or loose. First things first. Chuck

[jlevie]

More weight in the rear will create more oversteer. Not the other way around. The more rear weight bias, the more oversteer, and the more front weight bias the more understeer. All else being equal of corse just comparing weight distribution. Think of how 911s with their rear engine and rear weight bias oversteer and audis with their strong front weight bias understeer.

I agree with the part that taking weight off the front will help handling in general, but not for the reason you said, the logic behind it doesn't follow. And adding weight to the rear will definitely not reduce oversteer.

I'm sorry, but that is wrong. Oversteer is the result of insufficient grip by the rear tires. While there can be a number of reasons for that, moving weight to the rear tires will increase grip and reduce oversteer.

[jlevie]

Doesn't lower = lighter? The corner weights were "about" that, I didn't remember the exact numbers. But here they are. I think I'm going to try to eliminate a little weight in the front, but I don't think that's the root of the problem.

Tire pressures were 35 all around. Running Star Specs, not the spec tires.

It wasn't terrible, just...pretty loose. I will have to check toe and camber tonight, but I thought it was at zero. Rear camber isn't adjustable, is it? And I thought toe was only adjustable via ride height?

When corner balancing one adds weight to the light wheels. In this case (as is usual) the light corners are from the left front to right rear. Adding spring pads at either or both of those and/or taking spring pads out of the other diagonal will make the corner weights better. As will adding weight to the light corners.

The car as it sits now is nose heavy, so if you add weight you want it on the right rear corner. I don't know if the car is carrying ballast, but if it is moving the ballast to the right rear corner is something to consider.

To adjust the rear wheels you have to add adjusters to the trailing arm pivots. That can be eccentric bushings, which won't stay in adjustment, or weld in camber/toe adjusters. For some folks the weld in types will stay where you set them, but for most the to move. I put jack screw locks on mine to keep the toe setting from changing. IE has a new design intended to eliminate this problem, but I don't know of anyone with "race time" on a set.

[VinniE30]

I'm sorry, but that is wrong.

...

Oversteer is the result of insufficient grip by the rear tires.

Correct.

While there can be a number of reasons for that, moving weight to the rear tires will increase grip and reduce oversteer.

I don't agree that moving weight to the rear will reduce oversteer.
More weight in the rear will increase oversteer / reduce understeer.
More weight in rear is more mass that has to change direction in rear and hence less grip on rear tires and hence oversteer.

You're probably thinking of a scenario in a straight line drag race where weight in the rear would increase grip since the car is only going in a straight line.

Do some reading if you don't believe me.

from wiki:

In steady-state cornering, front-heavy cars tend to understeer and rear-heavy cars to oversteer, all other things being equal. The mid-engine design seeks to achieve the ideal center of mass, though front-engine design has the advantage of permitting a more practical engine-passenger-baggage layout. All other parameters being equal, at the hands of an expert driver a neutrally balanced mid-engine car can corner faster, but a FR layout car is easier to drive at the limit.

[nrubenstein]

Doesn't lower = lighter? The corner weights were "about" that, I didn't remember the exact numbers. But here they are. I think I'm going to try to eliminate a little weight in the front, but I don't think that's the root of the problem.

Tire pressures were 35 all around. Running Star Specs, not the spec tires.

It wasn't terrible, just...pretty loose. I will have to check toe and camber tonight, but I thought it was at zero. Rear camber isn't adjustable, is it? And I thought toe was only adjustable via ride height?

SE30 now allows adjusters in the rear. The real issue, though is that the parts bend. Mike's SE30 was at zero toe a couple years ago, and it just migrated. (No adjusters to blame in this case, either.)

[nrubenstein]

Also, Vinni, quoting Wikipedia in in general isn't a good way to win an argument.

[priapism]

...

Correct.

I don't agree that moving weight to the rear will reduce oversteer.
More weight in the rear will increase oversteer / reduce understeer.
More weight in rear is more mass that has to change direction in rear and hence less grip on rear tires and hence oversteer.

You're probably thinking of a scenario in a straight line drag race where weight in the rear would increase grip since the car is only going in a straight line.

Do some reading if you don't believe me.

from wiki:

Link to said article?

In an ideal situation, you want equal weights on all corners, hence the MR layout. That description seems very simplified.