experiences with oversteer

[rob101]

hello everyone,

This morning i had a bit of a wet road power oversteer incident, wasn't that hard to catch but the people sitting at the bus stop probably thought i was a maniac. It got me thinking the e34 seems fairly well balanced, although it did snap back a bit when i countersteered it think that was due to the open diff. There was also another time in the wet were i the seemed to oversteer a bit exiting a roundabout here which has shocklingly off camber ends to it (you see that roundabout is more like an oval) at that time i caught it easily as well. Since i can't really drive very well i figure, the e34 must be a fairly well balanced car although it helps that i have r17/45 235s all round. What does the board think and do other people have similar sideways experiences?

Rob

[liquidtiger720]

When I was about 16, I was still learning how to drive...in my e34. :) I guess I had bald tires on, and I gave the car too much gas off the line and into a turn. The rear end snapped out...and I paniced, over corrected which snapped it back the other way and did the same thing. I found myself heading straight toward a curb, but I somehow got it under control to avoid it. So yea...there's oversteer alright but ever since then I've found it easy to control.

[Jay 535i]

I do that all the time -- on purpose, mind you. I love flicking the tail out just a bit. Not crazy sideways action, but just a little oversteer like you're describing to keep things interesting. The M30 has just enough low-down torque to break things away nicely at low speeds on a wet road.

The E34 is known as being one of the most controllable and progressive sliders ever made. It certainly flatters the driver, and makes these kinds of antics relatively safe.

The bigger rubber you have would actually make the car HARDER to control in this situation, not easier. The extra grip raises the stakes and makes for a less progressive transition into and out of oversteer. The agressive "snap" you mentioned is probably down to that rubber.

[angrypancake]

My first sideways experience ended up with a tree and a totalled 525im. Since then I've learned to control those sideways times, mostly by practicing in parking lots at 4am in the snow. It can be fun if you know what youre doing, but terribly dangerous if you dont. The e34 is very well balanced, and some slight oversteer can make things interesting.

[Jeff N.]

All things considered, the E34 is easier to control in an oversteer situation than a lot of cars. Things is has going for it include:

- longer wheelbase
- reasonable weight balance front to rear
- not a ridiculous amount of power

In the dry, it's pretty hard with these cars to get power oversteer. Just too much tire, weight and not enough power (insert comment from Martin here about Jeff's cam). You can get what's called trailing throttle oversteer - that's the effect when in a corner and you lift the throttle slightly, the tail steps out and the car rotates to the inside of the corner. Trailing throttle is dangerous in that it's what will typically cause a driver to spin to the inside of a turn when you overcook the entry to a turn (slow in, fast out...be safe, huh?)

Rob, what likely got your car to snap back is not the open diffy. I suspect when the tail rotated out in the wet, it may have gone further than you expected. Typical driver response to that is to abruptly lift the throttle to stop power oversteer. When done abruptly, this will stop the oversteer while at the same time shifting all the weight forward which digs in front tires and unloads the rear leading to the snap back the other direction. Next time, try breathing just a bit off the throttle vs. a full lift. This should be more effective. (I'd really suggest a drivers school and try this on a wetted down skid pad - harmless place to sort all this out vs. the street).

More than oversteer, in stock form, the E34 plows like pig with understeer. Understeer of course is a much safer handling tendency than oversteer because the natural driver reaction is also the correct response to recover the car. It's when you start modding it up that the E34 gets a little twitchy. But twitchy is very relative to what it could be - lots of cars are famous for being a lot worse.

So..yup...all things considered, the E34 is a pretty smooth and safe ride.

[rob101]

I am not really sure if i backed off completely, but i think i may have hit a dry patch, because i heard your usual no traction in the wet noise which is fairly quiet then the tyre started to squeel like it had picked up on dry road. It oversteered mainly because i was in first gear hehe but i probably only gave it 3/4 throttle. You know, one of those places on the way to work where you just can't help yourself. seem to have alot of wet weather antics around that spot. i have lost traction in my e28 in the wet alot around there, but that was fortunately going in a straight line.


All things considered, the E34 is easier to control in an oversteer situation than a lot of cars. Things is has going for it include:

- longer wheelbase
- reasonable weight balance front to rear
- not a ridiculous amount of power

In the dry, it's pretty hard with these cars to get power oversteer. Just too much tire, weight and not enough power. You can get what's called trailing throttle oversteer - that's the effect when in a corner and you lift the throttle slightly, the tail steps out and the car rotates to the inside of the corner. Trailing throttle is dangerous in that it's what will typically cause a driver to spin when you overcook the entry to a turn (slow in, fast out...be safe, huh?)

Rob, what likely got your car to snap back is not the open diffy. I suspect when the tail rotated out in the wet, it may have gone further than you expected. Typical driver response to that is to abruptly lift the throttle to stop power oversteer. When done abruptly, this will stop the oversteer while at the same time shifting all the weight forward which unloads the rear leading to the snap back the other direction. (trailing thottle situation). Next time, try breathing just a bit off the throttle vs. a full lift. This should be more effective. (I'd really suggest a drivers school and try this on a wetted down skid pad - harmless place to sort all this out vs. the street).

More than oversteer, in stock form, the E34 plows like pig with understeer. Understeer of course is a much safer handling tendency than oversteer because the natural driver reaction is also the correct response to recover the car. It's when you start modding it up that the E34 gets a little twitchy. But twitchy is very relative to what it could be - lots of cars are famous for being a lot worse.

So..yup...all things considered, the E34 is a pretty smooth and safe ride.

[SC David]

I've had some fun experiences with oversteer. My first one resulted in me countersteering too hard and having the car snap back the other direction, and hit a curb going about 3mph. Minimal paint damage as I grazed a chainlink fence. No one was around, but I was still embarrased. That scared me into driving slowly during the rain. Since then I've been more careful and have learned how to properly countersteer.

[Alexlind123]

Normally, i can easily initiate safe and controlled power oversteer upon corner exit when that is the objective in mind. Once however, it caught be by surprise and i lifted off the throttle and went a little more into a parking lot that i had planned on; it turned out fine though i guess im just lucky the parking lot was there. The point is, when i want the car to do something, it will do it without hesitation and in a safe and predictable manner, even on dry pavement. I have never experienced any sort of understeer even on gravel, where it would be most noticable. This could be due in part to the fact that my suspension is not entirely stock.

[Zeuk in Oz]

Rob, reading between the lines I get the impression that this episode took you a little by surprise and has unsettled you.

May I suggest that you investigate the availability of advanced driving courses in Brisbane - BMW even hold them at Queensland Raceway - Advanced 1 costs $660 for the day using their cars. See www.bmw.com.au for details.

More experience will make you more able to adapt appropriately the next time something like this happens.

Alternatively, find a dusty paddock somewhere and have some fun getting to know your car.

[rob101]

It was scary and exciting at the same time lol, I am not that unsettled but i think i will have to do some kind of course as something like this could happen one day when i don't expect it ie when i am in torrential downpour traveling home on the freeway, which happens more than you think it would in brisbane. yeah i have read up on the BMW courses before mmmmmmm e46 325i mmmm. Queensland BMW club goes to an advanced course as well but you take your own car and it only costs around 150.


Rob, reading between the lines I get the impression that this episode took you a little by surprise and has unsettled you.

May I suggest that you investigate the availability of advanced driving courses in Brisbane - BMW even hold them at Queensland Raceway - Advanced 1 costs $660 for the day using their cars. See www.bmw.com.au for details.

More experience will make you more able to adapt appropriately the next time something like this happens.

Alternatively, find a dusty paddock somewhere and have some fun getting to know your car.

[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 (http://www.autozine.org/technical_school/handling/tech_handling_4.htm) 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 (http://www.autozine.org/technical_school/handling/tech_handling_4.htm) 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 :)

[rob101]

yeah as i said, its complicated. I think its a bit misleading Slip angles are important but to say that they are the cause of oversteer/ understeer (ie to define based on them)is like saying okay so weight never gets transferred around the 4 tyres and wheels never change their camber. ie the "grip" (ability of the tyre to create lateral force) is only dependant on slip angles, which isn't true. I guess its used because its an easy definition a one size fits all cop out, i am not saying its not correct, but i think it is ambigious.

For example imagine a car is steered instaneously away from straight ahead, ie the front slip angle is the steer angle and the rear slip angle is zero because you haven't started to turn. so that means this is understeer? no it doesn't.

[Jeff N.]

In the end, if the rear slips prior to the front, you have oversteer. And vice versa. How to you get to what end slips *is* complicated. And not static.

Usually what causes a mishap (as they were being discussed way earlier in the thread) is due lack of a fundamental understanding of what happens to the car when the driver modifies an input. Drivers on a constant line tend not to crash. If you don't understand the very basics of dynamic weight transfer, friction circles, and slip angles then you don't have much a chance of predicting what your car will do.

Of course the simple answer is to drive at 2/10ths of the car's ability as most do a day to day basis. Short of other idiots aiming at your space on the road there's not much to worry about then. :D

[rob101]

agreed, but i think car control is a skill that comes from practice rather than knowing the theory. Designing and tuning car's handling is something that can only come from theory or empirical knowledge (which is the more costly option hehe).


In the end, if the rear slips prior to the front, you have oversteer. And vice versa. How to you get to what end slips *is* complicated. And not static.

Usually what causes a mishap (as they were being discussed way earlier in the thread) is due lack of a fundamental understanding of what happens to the car when the driver modifies an input. Drivers on a constant line tend not to crash. If you don't understand the very basics of dynamic weight transfer, friction circles, and slip angles then you don't have much a chance of predicting what your car will do.

Of course the simple answer is to drive at 2/10ths of the car's ability as most do a day to day basis. Short of other idiots aiming at your space on the road there's not much to worry about then. :D

[Jeff N.]

A bit of basic car control theory - again, the general effects of throttle and brake on weight transfer and friction circle, etc - go a long way to help a driver understand what's occuring with their car.

Theory won't make you proficient; you need practice for that.

I've seen skills days taught both with and without 'ground school'. Ground school of course being a basic crash course in theory. Driver's improvement are much better with some ground school.

Planning your suspension is something you absolutely need theory for.


agreed, but i think car control is a skill that comes from practice rather than knowing the theory. Designing and tuning car's handling is something that can only come from theory or empirical knowledge (which is the more costly option hehe).

[R1daveg]

IMO the control of throttle in oversteer is an art in itself. A method for recovery which doesn't take as much learning, and is less upsetting to the cars weight transfer, is to use the clutch (if u have one..)
My E34 is auto, but still very predictable in oversteer in mild amounts in the wet (not really enough kw's in a M50 to power oversteer 235/17/45 rubber...;) ) and much more controlled in sports mode.
I dont drive it like that often (un-BMW-like behoviour!!), just often enough to keep the skill up.

[Maki]

Left-foot braking while maintaining throttle or easing off *very* gently will settle an oversteering RWD car.

The left-foot braking technique tends to lock up the undriven wheels -- the rears on an FWD car (helping the car pivot) or the fronts on an RWD car (inducing a degree of understeer and settling the car down). Throttle prevents lockup on the driven wheels and enhances rear-axle traction (with RWD) by keeping the front axle from loading up too much.

ABS will keep the front wheels from locking up completely, but you will get repeated, momentary lockup under low-traction conditions.

[Torque]

One of my experiences with oversteer resulted in a scratched bumper moulding and a scratched Nissan Altima. Lesson I learned from it is: 1 lane is not nearly wide enough to execute a proper drift.

[Jon K]

I am extremely anti-oversteer.

[dacoyote]

....to execute a proper drift.

Dude... you said that .... Drifting word....

[rob101]

I am extremely anti-oversteer.

so are most people, as for Left foot braking, i think i will pass, last time i tried to brake even slowly with my Left foot i almost when through the windscreen.

[Torque]

Dude... you said that .... Drifting word....
Yes I did. Now if you could just get over my username ...