Oversteer!

[nrubenstein]

Could you make it clear your stance on increasing weight in the front vs increasing weight in the rear and how it affects understeer and oversteer.
What you said here makes it sound like you agree with me. Loosing that weight in the rear than the front, which can "unbalance" them, would result in less oversteer / more understeer. IMO, for a better balanced car, it would be better to take weight from the front, but of corse that's not always possible. Optimal weight distribution for racing is actually a rear bias.

My stance is that when the car has been dramatically lightened in the back (like most BMW race cars), you often get more oversteer. Especially when the suspension has not been reconfigured to match. (Hint: SE30 uses street car springs, shocks and sways.) Before I nailed down the setup, my 323 was dramatically less stable on track when I converted it to a race car. (Zero suspension changes - just gutted and caged.) Add a ton of weight behind the rear axle, and you can also add oversteer. It depends on how much, on where you add the weight, and on how far off the car is in the first place.

[nrubenstein]

Either way it does not reduce oversteer. It reduces understeer.
Why do you think 911s are known to oversteer? They have the engine over the rear axle. that's why they designed the suspension and have huge rear tires to compensate for that weight at the rear.. Because a lot of people were crashing them because they oversteer so easily.

And just so there's no confusion over this, I agree that moving weight from the front to the back will be beneficial to you, because you will have a better weight distribution than before.(more rear bias than before.) The ideal weight distribution for racing is actually a rear bias, for less understeer.
You're doing the right thing, but your reasoning is wrong.

As someone who has spent a fair amount of time behind the wheel of a 911, I just need to correct this:

911s are not simply known for oversteer. That's a massive oversimplification. The reality is vastly more complex. Under certain circumstances, especially trailing throttle, the massive weight behind the rear axle does cause oversteer. The thing is, though, that under other circumstances (especially under power), they become very neutral to understeery. That's why 911s are so fast. It's because all that weight on the drive wheels improves traction when driven properly.

Edit: And while I agree that you tend to want a rear bias for racing, your reasoning is oversimplified in the best possible reading.

[priapism]

And just so there's no confusion over this, I agree that moving weight from the front to the back will be beneficial to you, because you will have a better weight distribution than before.(more rear bias than before.) The ideal weight distribution for racing is actually a rear bias, for less understeer.
You're doing the right thing, but your reasoning is wrong.

So I'm complaining about a car that is excessively oversteerey and your solution is to do something that will, in your mind, increase oversteer. Gotcha.

[Holland]

Because they think moving weight to the rear of the car will reduce oversteer when it in fact does the opposite (increases oversteer / decreases understeer)
And we shouldn't wrong info on the forum.

Honestly, I didn't want to chime in on this thread because although I am overly fascinated with driving theory, I have very little seat time driving a car hard. In a general consensus you are correct, but there are many other factors to consider.

Yes a 911 is a pendulum, no arguments there, but that is due to the fact that the entirety of its weight is behind the rear wheels.

You first state that moving weight to the rear increases oversteer, yet imply that a rear bias is ideal. This is more or less confusing is all.

There is more to handling than just shifting weight around. The semi rear trailing arm suspension for example. It behaves in a distinct manner, increasing camber and toe under compression. This does effect mid corner behavior.

In the case of OP, he is wanting to reduce oversteer and I agree as well with shifting some weight to the rear of a nose heavy car. This will make the car more balanced and theoretically more predictable. While this doesn't entirely fix oversteer, he will be better able to read the car mid corner and adjust accordingly. He is still driving a front engined car, and moving a minute amount of weight to the rear will not give 911 handling characteristics.

I'm not trying to tear you apart. It just seemed to me you are digging yourself a large hole.

[VinniE30]

Honestly, I didn't want to chime in on this thread because although I am overly fascinated with driving theory, I have very little seat time driving a car hard. In a general consensus you are correct, but there are many other factors to consider.

Yes a 911 is a pendulum, no arguments there, but that is due to the fact that the entirety of its weight is behind the rear wheels.

You first state that moving weight to the rear increases oversteer, yet imply that a rear bias is ideal. This is more or less confusing is all.

There is more to handling than just shifting weight around. The semi rear trailing arm suspension for example. It behaves in a distinct manner, increasing camber and toe under compression. This does effect mid corner behavior.

In the case of OP, he is wanting to reduce oversteer and I agree as well with shifting some weight to the rear of a nose heavy car. This will make the car more balanced and theoretically more predictable. While this doesn't entirely fix oversteer, he will be better able to read the car mid corner and adjust accordingly. He is still driving a front engined car, and moving a minute amount of weight to the rear will not give 911 handling characteristics.

I'm not trying to tear you apart. It just seemed to me you are digging yourself a large hole.

I think you missed this:

And just so there's no confusion over this, I agree that moving weight from the front to the back will be beneficial to you, because you will have a better weight distribution than before.(more rear bias than before.) The ideal weight distribution for racing is actually a rear bias, for less understeer.

I agree with most of what you said here.
I never said that oversteer is a bad thing. Generally oversteer is preferred over understeer in racing. Almost all street cars are designed to have understeer for safety reasons.
My argument was with some people thinking that adding/moving weight to the rear of the car will reduce oversteer.
Doing this is good and it will have good results! - you will have less understeer and better turn in! The car will be better balanced.
..but the logic that it decreases oversteer is flawed and not correct.
Moving weight from the front to the back is good because it reduces understeer.
Is that clear enough?

[Holland]

I agree with most of what you said here.
I never said that oversteer is a bad thing. Generally oversteer is preferred over understeer in racing. Almost all street cars are designed to have understeer for safety reasons.
My argument was with some people thinking that adding/moving weight to the rear of the car will reduce oversteer.
Doing this is good and it will have good results! - you will have less understeer and better turn in!
..but the logic that it decreases oversteer is flawed and not correct.
Is that clear enough?

I see what you are saying, and it is true, but I also think it's a bit more complex than that. In terms of inertia you are completely correct, but I also think that if you put some weight bias in the rear, in the correct placement of course, it won't be enough to send the car into oversteer because the traction gain would be more beneficial.

[priapism]

I see what you are saying, and it is true,

It's not.

In any case, corner balancing often has little to do with the actual weight or ballast and more to do with ride height in different corners, as I touched on earlier.

[priapism]

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.

Yup, you nailed it.

Unfortunately I was getting all tied up on crossweights and didn't discover this until last night--and I have to leave for my first race in a few hours. Meh, winning is overrated.

[priapism]

Actually, rear toe was fine.

Before the last race I surmised that I might have been bottoming out under power. It didn't feel like I was hitting the bump stops hard, but when you're on the power it would change the handling, so I figured it might have been settling on the rear stops. Either that or I was getting camber gain in the rear, causing a lack of rear grip. I put some pads in the rear (both sides) and frankly I had a little too much understeer at this last race! The car had to go to the shop and get a whole bunch of Spec Miata impact damage pounded out, but before Willow I'm going to try stiffening the rear bar up a bit to try and get it back to neutral. Buttonwillow doesn't have the super tight 90-degree corners that Cal Speedway has (the corners that it was kicking the butt out on) but in the Grapevine section I didn't get any kick out of the rear end, so I think I may have nipped that in the bud.

Just wanted to revisit this thread in case anyone went searching for handling fixes. No pads + H+R Race springs = potentially no bueno. I'm going to stiffen the rear sway for now, then get it on scales once I get it home, and if I'm way off maybe put smaller pads in one or both rear ends.

[mrbobian]

Glad you figured it out! Thanks for the update.

Its funny how riding the bumpstops isn't that fun for either a race car or street car. Who'da thunk.