experiences with oversteer

[Anton CH.]

Its pretty difficult to get the e34 to oversteer with stock suspension geometry. As previously stated the car is heavily tuned to understeer. Such understeer in a rwd is a liltle dangerous in my opinion b/c most drivers countersteer which results in the car snapping back the other way uncontrollably. If you ever find the rear end coming out, just let go of the steering wheel (not completly but let it turn on its own) and the rear end will quickly gain traction rather smoothly. Just try it, it's fun!

[Alexlind123]

Its pretty difficult to get the e34 to oversteer with stock suspension geometry. As previously stated the car is heavily tuned to understeer. Such understeer in a rwd is a liltle dangerous in my opinion b/c most drivers countersteer which results in the car snapping back the other way uncontrollably. If you ever find the rear end coming out, just let go of the steering wheel (not completly but let it turn on its own) and the rear end will quickly gain traction rather smoothly. Just try it, it's fun!

Are you sure youre talking about understeer? If a car is understeering i would not expect a tendancy to countersteer, because understeering is where the car is not steering enough whereas oversteering is the car steering too much. Maybe im wrong. If so, please correct me.

It has been my experience that most BMWs have a tendancy to oversteer. On the e34, the rear sway bar is much smaller than the front to help combat oversteer.

Maybe someone who knows more about this than i do can explain it better.

[rob101]

Rear sway bars are usually smaller than the front in RWD cars, I think this is partially because the rear has naturally less traction when driven. I used to know this stuff, I'd have to look it up though to be sure.

Oh boy don't get me started about suspension design i did a thesis on a program to simulate handling of a Formula SAE car last year. it is a headache waiting to happen.

[Anton CH.]

If you want oversteer, install bigger sway bar. If you want more understeer, install bigger front bar. Golf owners install 28mm bars on the rear to remove understeer!
When the rear breaks traction most drivers expect the rear end to slide out but since stock cars are tuned for understeer, the car does not really slide as much as drivers think. I know a few people that got in trouble not because the car spun out but because they over reacted and countersteered too much-the car just snaps the other way. The snapping back is always much more violent than the initial slide because so much energy is stored in suspension and tire sidewall.

Suspension design sounds interesting, especially for something like Formula cars. I am sure it becomes very complicated quickly.

[mattyb]

i think its important and commendable that you recognise the driver skill element in this situation. i once put my hq ss monaro around a pole in the wet. nothing to do with under/oversteer, just young and stupid and invincible. regardless of setup and everything else on the car the bottom line on losing control is that it is totally a result of the drivers actions. I am not trying to give u a hard time, far from it because weve all been there, but im sure the next time in the wet your driving style will be different and you will be conscious of the fact that how u apply the throttle and at what speed u approach hazards and differing road conditions is a decision for u and not the car. damn am i just getting old or what!

[rob101]

Yeah i understand completely, it does help having a good car that is reasonably stable, but unfortunately you sometimes get into situations that are unexpected i am very careful when there is alot of water on the road because the drainage on the roads here is shitehouse. But i understand what you mean i guess it is about knowing your car's and your own limits so that you can avoid overstepping them and writing off your car. Thankfully i didn't do anything too stupid, it was a deserted road early in the morning, but it did catch me a bit off guard. I think most people in Australia will agree that most people with licences in this country don't know enough about driving, as evidenced by what happened this christmas which is what happens when you try and teach a one-dimensional approach to road safety focusing exclusively on speeding. but that is another topic all together

i think its important and commendable that you recognise the driver skill element in this situation. i once put my hq ss monaro around a pole in the wet. nothing to do with under/oversteer, just young and stupid and invincible. regardless of setup and everything else on the car the bottom line on losing control is that it is totally a result of the drivers actions. I am not trying to give u a hard time, far from it because weve all been there, but im sure the next time in the wet your driving style will be different and you will be conscious of the fact that how u apply the throttle and at what speed u approach hazards and differing road conditions is a decision for u and not the car. damn am i just getting old or what!

[Jeff N.]

Some of you guys need to get your theory correct. A few definitions.

Understeer occurs front slip angle is greater than the rear slip angle.
Oversteer occurs when the rear slip angle is great than the front slip angle.

See Here if you want get the whole theory.

Sway bars effect slip angles by changing the relative load on the tires effecting grip and therefore slip angles. A bigger front bar will tend to lift the inside front tire before the inside rear tire. This will increase the slip angle in the front causing understeer. Reverse the effect for a bigger rear bar.

When your car makes a sudden transition (say a snap to the other side in an oversteer situation), this is primarily due to an abrupt change in the relative weight distribution on the tires due to either a throttle modification, pavement change, or braking modification. Here's a typical scenario:

- Car is in power oversteer. (Rear tires are sliding due to excess torque, fronts are not sliding) This means the rear tires are loaded as the car is accelerating. Driver is counter steering to mitigate the tail out condition.
- Car starts to over rotate beyond drivers ability to countersteer.
- Driver recognizes overrotation and ...without realizing what they are doing.
- Lifts throttle quickly and significantly to keep car from overrotating.
- Weight shifts from rear to front tires upon deceleration significantly unloading rear tires due to weight transfer.
- Front tires which were never slipping now have even greater traction due to weight transfer forward.
- Front tires grab and shoot car in direction of counter steer as unloaded rear tires which have minimal traction due to load loading allow back end to rapidly rotate (skid) to the other side.

This creates the snap oversteer you are talking about.

The correct response to this situation is to *not significantly lift* the throttle and unsettle the car. This of course is a finese response and your success is completely dependend on how fast the car is rotating and if you can correctly adjust the throttle such that you can hold the oversteer angle (ie balance the car).

This is why oversteer is tricky. It's a) counterintuitive to correct and b) difficult in practice to do. The faster you go the more difficult it is to manage. Pavement changes etc only make more difficult as the friction circle changes.

We see this all the time when we teach drivers skills days. Go to one. Get some theory. Try some theory. But, don't guess - the results aren't worth it.

[Alexlind123]

This is what i was looking for. It seems that my theory agrees with yours, i think anton just got oversteer and understeer mixed up.

Some of you guys need to get your theory correct. A few definitions.

Understeer occurs front slip angle is greater than the rear slip angle.
Oversteer occurs when the rear slip angle is great than the front slip angle.

See Here if you want get the whole theory.

Sway bars effect slip angles by changing the relative load on the tires effecting grip and therefore slip angles. A bigger front bar will tend to lift the inside front tire before the inside rear tire. This will increase the slip angle in the front causing understeer. Reverse the effect for a bigger rear bar.

When your car makes a sudden transition (say a snap to the other side in an oversteer situation), this is primarily due to an abrupt change in the relative weight distribution on the tires due to either a throttle modification, pavement change, or braking modification. Here's a typical scenario:

- Car is in power oversteer. (Rear tires are sliding due to excess torque, fronts are not sliding) This means the rear tires are loaded as the car is accelerating. Driver is counter steering to mitigate the tail out condition.
- Car starts to over rotate beyond drivers ability to countersteer.
- Driver recognizes overrotation and ...without realizing what they are doing.
- Lifts throttle quickly and significantly to keep car from overrotating.
- Weight shifts from rear to front tires upon deceleration significantly unloading rear tires due to weight transfer.
- Front tires which were never slipping now have even greater traction due to weight transfer forward.
- Front tires grab and shoot car in direction of counter steer as unloaded rear tires which have minimal traction due to load loading allow back end to rapidly rotate (skid) to the other side.

This creates the snap oversteer you are talking about.

The correct response to this situation is to *not significantly lift* the throttle and unsettle the car. This of course is a finese response and your success is completely dependend on how fast the car is rotating and if you can correctly adjust the throttle such that you can hold the oversteer angle (ie balance the car).

This is why oversteer is tricky. It's a) counterintuitive to correct and b) difficult in practice to do. The faster you go the more difficult it is to manage. Pavement changes etc only make more difficult as the friction circle changes.

We see this all the time when we teach drivers skills days. Go to one. Get some theory. Try some theory. But, don't guess - the results aren't worth it.

[rob101]

yes it was a typo i assumed.
an easier way to understand why bars do what they do is to understand that having a higher roll stiffness at the front of the car increases the weight transfer from the inside to the outside wheel (its called elastic weight transfer and its what allows people to tune the handling of a car when it is in steady state (mid corner)), Since a tyre's maximum lateral force increases with vertical load but not in a linear fashion, that is double the vertical load does not mean double the lateral force in fact it will be less than double, so in fact if you have a set of tyres equally loaded with 50 kg each and another set with 25 and 75 kg the unequally loaded tyres will have less max lateral force for the same total weight on the axle.

So by increasing the load transfer on the tyres by stiffening the springs/roll bars (thus increasing roll stiffness) at one end of the car you decrease its grip relative to those at the other end.

I don't agree totally with the slip angle definition, and i don't remember seeing that defintion in books on the matter ie those by Caroll Smith, Milliken and Staniforth. If you seriously want to know about handling etc. those are the authors to read, but as i said make sure you have some painkillers because its not an easy thing to understand in totality.

[Jay 535i]

yes it was a typo i assumed.
an easier way to understand why bars do what they do is to understand that having a higher roll stiffness at the front of the car increases the weight transfer from the inside to the outside wheel (its called elastic weight transfer and its what allows people to tune the handling of a car when it is in steady state (mid corner)), Since a tyre's maximum lateral force increases with vertical load but not in a linear fashion, that is double the vertical load does not mean double the lateral force in fact it will be less than double, so in fact if you have a set of tyres equally loaded with 50 kg each and another set with 25 and 75 kg the unequally loaded tyres will have less max lateral force for the same total weight on the axle.

So by increasing the load transfer on the tyres by stiffening the springs/roll bars (thus increasing roll stiffness) at one end of the car you decrease its grip relative to those at the other end.

I don't agree totally with the slip angle definition, and i don't remember seeing that defintion in books on the matter ie those by Caroll Smith, Milliken and Staniforth. If you seriously want to know about handling etc. those are the authors to read, but as i said make sure you have some painkillers because its not an easy thing to understand in totality.

I think that's all true. At least, it jibes with what I learned in my R/C car days