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Old 09-29-2003, 06:25 PM   #1
bigDvette
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Default Oversteer vs Understeer

This year I bought a set of 315/35/17s and 335/30/17 Kumhos on 17x11 17x12 CCW rims. Great setup, really sticks well with that much tire.

After about 5 events I corded the fronts on the outside edge, the wear was really uneven.

So I slapped a set of new shaved Kumhos on this week and got an alignment and increased the Camber from -1 to -1.2 and set the toe to 0.

Went to the time trials this weekend and the car really turned in great. However, i noticed I was overdriving the rear. So I have a theory.

If by putting more camber in the front I increased the contact patch to stop using the outer edge so much, I probably increased the grip. I can't push the car at all. However, since the front grips so well, when I would normally be drifting a bit in a tight turn, it feels more like the rear is oversteering.

does that make sense. Would my solution to re-balance a bit to add air up front (have to be careful here) or go to a bit stiffer sway bar than the stock z51 front?

Anyone's input welcome. Well almost anyone's.
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Old 09-29-2003, 09:15 PM   #2
urtoslo
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Default Re: Oversteer vs Understeer (bigDvette)

D,

It's a little unclear (for me) what is happening to your car. Pushing to me is understeering (the car not wanting to make the turn), and you don't want to be doing that in an autox. When it understeers, you have to slow way down to get it to turn or mash the throttle to get around, not fast or smooth. Overdriving the rear? You want the car to oversteer rather than understeer, as you want to get through the turns as fast as you can. Oversteering can spin the car out if you are not careful, but is faster as you are not fighting it to turn in the first place. To me, oversteer and understeer are something the car does as a whole, not one end understeering and the other oversteering. Maybe I'm just being thick here...

I never found tire pressure much use in getting rid of understeer.

Does your car still understeer? Adding a larger rear sway bar, or keeping the rear size the same and decreasing the size of the front sway bar, will increase oversteer and reduce understeer.

I would make one change and see what it does before you try another change.
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Old 09-29-2003, 09:26 PM   #3
jayleone
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Default Re: Oversteer vs Understeer (bigDvette)

What tire pressures are you running? Before and after each run? I find that once my hoosier Rs go above 30PSI I get all kinds of understeer or pushing, I'm confused too, but the point is the car won't turn.
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Old 09-29-2003, 11:08 PM   #4
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Default Re: Oversteer vs Understeer (bigDvette)

add more camber to the rear as well
and you will have more grip there.

Quote:
This year I bought a set of 315/35/17s and 335/30/17 Kumhos on 17x11 17x12 CCW rims. Great setup, really sticks well with that much tire.

After about 5 events I corded the fronts on the outside edge, the wear was really uneven.

So I slapped a set of new shaved Kumhos on this week and got an alignment and increased the Camber from -1 to -1.2 and set the toe to 0.

Went to the time trials this weekend and the car really turned in great. However, i noticed I was overdriving the rear. So I have a theory.

If by putting more camber in the front I increased the contact patch to stop using the outer edge so much, I probably increased the grip. I can't push the car at all. However, since the front grips so well, when I would normally be drifting a bit in a tight turn, it feels more like the rear is oversteering.

does that make sense. Would my solution to re-balance a bit to add air up front (have to be careful here) or go to a bit stiffer sway bar than the stock z51 front?

Anyone's input welcome. Well almost anyone's.
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Old 09-30-2003, 01:09 AM   #5
John B
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Default Re: Oversteer vs Understeer (bigDvette)

Oversteer is when the passenger is scared. Understeer is when the driver is scared. :eek:
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Old 09-30-2003, 09:38 AM   #6
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Default Re: Oversteer vs Understeer (John B)

Quote:
Oversteer is when the passenger is scared. Understeer is when the driver is scared. :eek:
:lolg: :lolg:

I'd suggest 1/32 toe-in of the rear to reduce the oversteer. It'll make the rear sit as you exit and mash it.
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Old 09-30-2003, 10:44 AM   #7
Jim 47
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Default Re: Oversteer vs Understeer (bigDvette)

Quote:
This year I bought a set of 315/35/17s and 335/30/17 Kumhos on 17x11 17x12 CCW rims. Great setup, really sticks well with that much tire.

After about 5 events I corded the fronts on the outside edge, the wear was really uneven.

So I slapped a set of new shaved Kumhos on this week and got an alignment and increased the Camber from -1 to -1.2 and set the toe to 0.

Went to the time trials this weekend and the car really turned in great. However, i noticed I was overdriving the rear. So I have a theory.

If by putting more camber in the front I increased the contact patch to stop using the outer edge so much, I probably increased the grip. I can't push the car at all. However, since the front grips so well, when I would normally be drifting a bit in a tight turn, it feels more like the rear is oversteering.

does that make sense. Would my solution to re-balance a bit to add air up front (have to be careful here) or go to a bit stiffer sway bar than the stock z51 front?

Anyone's input welcome. Well almost anyone's.
Seems very clear to me. Before camber and tire change, the car was basically neutral in its handling. After increasing the camber on the front and the new shaved tires the car does not understeer, but it feels like the rear wants to come around (oversteer) more than it did before.

Tire pressure can help to rebalance the car's handling characteristics, but first you have to know the "best grip" tire pressure. Do you know this pressure? Knowing this pressure, you can now start increasing or lowering the pressures to increase or decrease grip on either end of the car.

A simple way to rebalance your car is to also increase the camber in the rear, which will provide you the more evan ware accross the tire that you desire, and also give you better grip on the rear to balance the increased grip you generated in the front by increasing the camber there. :cool:

Jim
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Old 09-30-2003, 11:02 AM   #8
zrracer
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Default Re: Oversteer vs Understeer (bigDvette)

I think you are saying that you have oversteer?

Tell us about the rear alignment,air pressure,sway bars and any suspension mods that you have made. Are you using R tires? How much of the rear tire are you using?

Robin
:cheers:
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Old 09-30-2003, 12:29 PM   #9
bigDvette
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Default Re: Oversteer vs Understeer (zrracer)

Jim 47 has it right. Before I increased the front Camber to get rid of eating up just the outside edge of the tire, the car felt very balanced. to me that meant that the car had no tendency to oversteer any more than understeer given I get in and out of the turn correctly and at the right speed.

However, now that I increased my camber up front to get even tire wear, the front turns in really well and is wearing the tire more evenly (meaning I'm getting more contact patch I hope). The rears are toed in .01 and have -.68 camber. I think that is right. I'm in Mexico City can't run out to the garage right now. The rear tires wear completely evenly edge to edge (marked with Chalk).

the new alignment seems to be giving me much more even tire wear up front and the same in the back (that is why I didn't change it this time), but the car doesn't seem as balanced. I'm ok hanging the rear out from time to time, but it almost seems as if the car is pivoting on the front tires because they have so much grip. Maybe that is impossible.

My suspension is z51 with Bilstiens lowered about 1/4" all the way around. The car was aligned with me in it (280 lbs so it makes a big difference) and otherwise handles incredibly well. Maybe I just need to put a bit more gas in to it later in the turn than I used to. If it is oversteering, stiffer front or more pressure up front will go the other way and begin to push. I guess smaller sway in the back or less pressures will help in the rear. Maybe it is just my underskilled foot. :D

Just checking my logic to see if these are the options.
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Old 09-30-2003, 01:23 PM   #10
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Default Re: Oversteer vs Understeer (bigDvette)

What pressure do you currently try to maintain in the back? If your front is sticking, I'd leave that setup alone and work with your rear.

:steering:
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Old 09-30-2003, 04:08 PM   #11
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Default Re: Oversteer vs Understeer (TedDBere)

28 psi in the rear to start, heating to about 32 at time trials which end up being about 4 -6 85 second laps.

Chalk shows almost perfect side to side to the wear arrows on the tread.
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Old 09-30-2003, 08:19 PM   #12
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Default Re: Oversteer vs Understeer (bigDvette)

Maybe I'm just different but I prefer to have the car a bit loose. If the the back comes out a bit and I can catch it by unwinding the wheel a bit without having to get out of the gas, I'm happy. I get through the turns quick and in situations where I come out of a turn on one side of the track and need to move quickly to the other side to setup for the next turn, a car thats a bit loose allows me to make that manuever quicker and easier.
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Old 09-30-2003, 08:19 PM
 
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