Our cars naturally understeer and most of us spend lots of time trying to get the front end to stick and turn in by using neg camber and whatever other means. Most of the time the rear is well controlled if you keep things soft enough but what is the actual mechanism of the sudden power on oversteer? Certainly driving smoothly helps avoid it but what is actually happening at the rear end to cause this ? I don't have enough power for this to be an issue in 3 rd gear unless in the rain but in 2nd gear hairpins etc it's a PITA and just slow you down. ( Looks neat though and the corner workers think you are going fast )

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'97 M6 Kenny Brown SFCs, Koni SA , Eibach Prokits ,LG adjustable PHB , 1LE LCAs , GW upper control arms, K&N FIPK , custom bent Hurst LS1 brakes and Torsen .

 

Simple tire physics. A tire cannot corner at maximum speed when some traction is being used for acceleration. The concept is called the "traction circle" and is explained in many books.

It's why Carroll Smith points out (in Drive to Win) that race cars must have some steady state understeer in order to accelerate out of turns. It's also why the really fast folks don't use big rear antiroll bars. Carroll also says (approximately) "Sliding the rear looks neat and feels fast to the novice. It's a shame it's not the fast way around the track." BTW, the corner workers know that.

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2000 Firebird convert, chameleon/tan, M5, Y87, TCS
KBDDs, BMR STB and Panhard, 245/50-16 GSCs

[This message has been edited by V6Bob (edited July 14, 2002).]

 

Its interesting isn't it that trailing throttle oversteer is quite useful in long steady state corners while power oversteer virtually never helps . I agree totally with the soft rear end set up to prevent this.

 

Rear tire slip aangle exceeds the front tire slip angle because the front tire only has to corner and the rear has to handle cornering as well as acceleration loads. FACT!

 

could it be cuz we don't have independent rear suspension?

also, i think the camaro weight distribution (not 50/50, more like 60/40) is creating a moment of inertia where the back is lighter and wants to come out more easily in turns than if we were at 50/50 (like a BMW 3-series)

i'm not crying about it, just trying to figure it out. Torsen T2R and 315s would definitely help! hopefully i'll be able to try that soon.

 

What V6Bob said.

Anything that adds bind to the rear suspension will reduce the total rear grip that you have to work with in friction circle/ellipse math. You wouldn't by any chance be running plain poly bushings back there in the LCA's, would you?

Norm

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'79 Malibu, way not stock (355, 5 speed, . . .)
'95 Mazda 626 V6 5 speed, not entirely stock either
'01 20th AE Maxima, 5 speed, stock (so far)

[This message has been edited by Norm Peterson (edited August 02, 2002).]

 

MrBigXL has the right idea but he's got it backwards, a weight bias towards the BACK of the car will increase the polar moment of inertia (you're center of rotation is in the front as long as they're still holding traction)

That's why fiero's were so dangerous if you weren't careful... they liked to swap ends.

v6bob has the right explanation, and in addition I'd add that in posi cars there's an added effect, when in a corner and on the throttle your posi unit is going to lock up and keep both rear tires turning at the same speed, this will have the net effect of breaking free your inside rear. Once the posi overcomes static friction (and the inside is already unweighted somewhat by weight transfer), you're essentially only resisting lateral acceleration with 1 tire... not a lot of grip to overcome at that point.
(even at low speeds you can hear this effect, ever wonder why your inside rear squeaks turning at an intersection when you hit the gas a little bit?)

 

i don't know too much about this subject but i will say what makes sense to me. so just say it i'm wrong. but would it help if you just had higher profile rear tires to allow the wall to flex in the turns

 

Definitions:

Understeer: "When the slip angle of the front tires exceeds that of the rear."

Oversteer: "When the slip angle of the rear tires exceeds that of the front."

A tire has only 100% of it's traction to provide. when you use up part of that traction by steering, it has less than 100% left for side load.

When you use up 100% of your tire's traction in side loading, it has none left for acceleration or braking, and the tire slides.

Hope this helps.

Garrett Waddell

 

What is "slip angle?"

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95z A4 3.23 89K
In order of install: PSlot rotors/PF pads, Flowmaster CB, Moroso CAI, descreened MAF, TB bypass, BMR STB, GMS LCA, 1LE sway bars w/Prothane Bushings, BMR SFC, cutout, BMR PHR

 

On our cars it is caused by a few things.
Not smooth with throttle
Poor posi
Rear swaybar too big.
Pretty simple stuff to remedy really.

And as I have always said IRS is over rated and would make the problem worse. Neg camber on one side is pos camber on the other when cornering. Even some of the best production IRS units have toe control problems. All IRS systems have less anti-squat than a solid axle setup. All advantages go to solid axle.

 

"All advantages go to solid axle."

Look, I agree that live axles are often put down too much. But that goes too far. Live axles have a disadvantage with large unsprung weight, which outweighs the advantages you give (maybe not by much). That's why, in any pavement racing series where IRS is allowed, it is used.

IRS is better, just not _that_ much better.



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2000 Firebird convert, chameleon/tan, M5, Y87, TCS
KBDDs, BMR STB and Panhard, 245/50-16 GSCs