Snap Oversteer

[jackson]

Hi, I was talking with friends the other day and the topic of oversteer came about. Most mentioned that most BMW accidents happened during or just after rain and that most of them happened to E46. They mentioned that usually it hit divider or went straight during a corner (from the skid marks they can see) or some other non-other-car involvement. It is usually because the car for no apparent reason became uncontrollable especially during corners and especially during or after rain.The only explanation I could offer was it may be prone to snap oversteer. Which is why I am posting. Has anyone heard of such cases? Is it bad driver (don't know how to handle oversteer), bad conditions/environment or bad car design? As for the bad driver reason, I assume that we all think we are good drivers but as can be seen from the video of the BMW Driver Training at SIC, most just spun-out or couldn't handle the oversteer that ensued (even though I think they were trying to provoke it and expected it to happen). It seems this kind of behavior is not only seen in the E46, but other models as well and the 1series is especially prone to this.Any thoughts anyone?

 

[fabianyee]

went straight during a corner is understeer...

Anyway, traction of a car depends a lot on the tyres used... wider tyres are more prone to aquaplaning/hydroplaning. So for those with big fat rims and tyres, be extra careful in the rain..

Maybe u can do a research based on the tyres and wheels combo used on their cars..

 

[Van1ty]

My last major BMW accident (was driving an e30 then) I crashed due to my inability to control my counter steer. Infact, if the car didnt oversteer my accident would have been much worse. =p Thank god for RWDs.

 

[turbology]

Speed.
Speed is the problem.
You can't correct oversteer or understeer if your forward momentum is greater than gripping force from all 4 of your tires.
Slow down before you enter corners.
Is always easier & faster to gain speed during corners than losing speed.

 

[ALBundy]

As for the bad driver reason, I assume that we all think we are good drivers but as can be seen from the video of the BMW Driver Training at SIC, most just spun-out or couldn't handle the oversteer that ensued (even though I think they were trying to provoke it and expected it to happen).

Any thoughts anyone?

In the video, the participants are taught to artificially induce an over-steering situation and then correct it.

Most participants DO NOT get it right the first time (like what you saw on the video) and hence that is where Driving Training comes into the picture, to impart theoretical knowledge and practical hands-on experience to all drivers so that when you in such a situation, you will know what to do!!

Cheers!

 

[ALBundy]

Speed.
Speed is the problem.
You can't correct oversteer or understeer if your forward momentum is greater than gripping force from all 4 of your tires.
Slow down before you enter corners.
Is always easier & faster to gain speed during corners than losing speed.

Oversteering has nothing to do with excessive speed. It happens when the vehicle does not have enough traction at the rear tires.

One good example is drifting.

Cheers

 

[AlexNg]

i think its driver problem first (unable to control) then only other related ones like car and so on

 

[astroboy]

Give the driver a ticket for failure to control the vehicle.

I was having fun with my other mini MPV which happen to be a RWD and on a wet corner, I push it a little to try get some oversteer thrill that wet morning on the way to work.

Both hands on the steering, 3 and 9 o'clock, upon exiting the corner my hands at about 2,8 o'clock, I can feel my rear move, I immediately counter and waited for the rear to recover. By this time, half my car is on the opposite lane, to my surprise, the moment my rear reacted to the counter, it bounces back and becoming an opposite oversteer.. I counter again and it took several counters to regain rear wheel traction and that time, the MPV almost come to a halt and yes, my right leg is off the acc pedal and no brake were used the whole time.

I was all over the road and lucky me, there's no traffic that moment. I then realise a body hugging seat would come in handy so my butt will not be all over the seat during the "action" so I can focus on the steering..

I am oredi on extra hard GAB shock at my rear, can it be not hard enough still ??

 

[turbology]

I am oredi on extra hard GAB shock at my rear, can it be not hard enough still ??

It might be you "counter" it for too long.
Eyes on the road, not the steering.
Point your wheels to the direction you wanted

 

[ALBundy]

Counter for too long and too much will induce a secondary oversteer aka fish tailing!

To correct oversteering, one needs plenty of practise. But then again, before you start practising, one needs to know what to do!

And it is partly because of this, most family saloon cars are made to have a slight understeer.

Cheers

 

[astroboy]

Ya man.... I was like a fish swimming with no direction..

I went buy a el-cheapo SIME Astar100 for my rear to get all these oversteer action..

Need to practice more.. I wonder if it will rain tomorrow..

Counter too long ya.. but if its dry, its a lot more easier to control because even the rear skid still have some traction compare to doing it in the wet. The rear just move out, so fast! Damn, I wish I have Stig's reaction..

Any huge car park around where we can practice in the wet? No divider, no trees, no walls, no on coming trucks.. ... and no need to pay RM1,700

 

[m43ldotcom]

i didnt any experience oversteer or understeer with my e28. aquaplaning once .... with s class on my tail .... straight away after regain grip move to the left so the s class can speed off.... till now rain or not rain upon reaching that place again i slow down instinctively ... haha.

understeer with kancil once ... almost hit that divider near jalan duta toll. i thought can take that corner like e28 ... forgot i'm driving kancil that time.

then i saw corolla altis (previous model) oversteer then turn into fishtail in front of me... nearly hit a trailer ... lucky that driver regain control again. it happen cause he want to overtake some iswara, at some corner @ plus highway. but i think he goes too fast and the rear tyre just lose grip ....

so i think it's better to know your car ability first.... but how to know your maximum ability if you did not try it, right ? drive safely!

 

[cempaka]

Actually Astroboy, the mistake you made there was to take your foot off the accelerator. Like Bundy said, oversteer is the rear wheels losing traction. When you lift accelerator or brake, the weight shifts to the front wheels (opposite effect of when you hit the gas) which reduces traction of the rear wheels (less weight pushing down on them). In a corner, this by itself can induce oversteer if going fast enough.

In this case, when your counter steer took effect, the rear tires weren't able to regain grip because they didnt have any weight on them, and continued to slide to the opposite side. With continued zero throttle, the MPV weight stayed all towards the front, so each time you countered, same thing happened, until you were finally going slow enough that the tires could grip.

A little bit of steady throttle would have shifted the weight towards the back and likely let your rear tires regain traction and taken you through the turn after your first counter. Of course, in the rain and with an MPV, the margins of error are much less, but it is the same principles, just with increased effect.

It is natural instinct for most people to lift throttle or even brake when they feel the rear end start to step out while cornering, but this actually makes the problem even worse, and is what causes "snap oversteer" aka "throttle-off oversteer" aka "lift-off oversteer" as at higher speeds it is very sudden and usually leads to a spin. So one of the key ways to control oversteer is not only counter steer, but also fighting one's instincts and learning to keep applying some throttle to increase the rear wheel traction. This of course takes lots of practice.

Most trained drivers can control normal oversteer at reasonable speeds. However, once snap oversteer begins at high speed, even professional drivers often cannot regain control, it's just too fast and too drastic, and you can see it happen occasionally at all levels of racing up to F1. The reason it doesnt happen more often is they take care to avoid it happening in the first place.

Definitely don't stiffen the rear more, as it actually makes the car more prone to oversteer. In fact, if the MPV is driven by other family members, I would recommend either returning the suspension to stock, or better yet sending them for a driver training course.

 

[astroboy]

Wow! So many sifu here... learned a lot. Of course, practice makes perfect! My missy seldom take the MPV unless she has to go out late at night for personal safety reason, otherwise she'll take the E90. And no worries, she's a better driver than me.. BlackE90 knows what I'm talking about..

The RWD MPV is my toy, my missy make me use the 1.3L MPV to keep my speed in check but what she didn't realise, I can have equal fun with any 4 wheels and I don't need to go fast to enjoy driving.. Heheheheheheee.....

Ok ok... for now focus on fishtail..

 

[turbology]

Oversteering has nothing to do with excessive speed. It happens when the vehicle does not have enough traction at the rear tires.

One good example is drifting.

Excessive speed can cause oversteer. Are you saying "oversteering has nothign to do with speed?"

FYI, Drifting is actually "some sort of understeer".

Like Bundy said, oversteer is the rear wheels losing traction.

Oversteer happen only when rear wheels slip angle is greater than front wheels.
"losing traction" is not technical correct.
Lifting throttle cause weight to shift to front (not all), and making rear wheels contact patch smaller, thus increasing slip angle, and result in oversteer.

Cheers

 

[ALBundy]

then i saw corolla altis (previous model) oversteer then turn into fishtail in front of me... nearly hit a trailer ... lucky that driver regain control again. it happen cause he want to overtake some iswara, at some corner @ plus highway. but i think he goes too fast and the rear tyre just lose grip ....

Most accidents are caused by an initial understeer. I believed the corolla was entering into the corner too fast and then once the corner he will try to turn in with excessive steering angle.

A perfect recipe to create an understeer situation!!

Most drivers will then apply brake and this will shift the weight of the car forward (and help to regain front end grip to steer the car) but this will then create a snap or secondary oversteer aka fish-tailing!!

Cheers

 

[ALBundy]

Excessive speed can cause oversteer. Are you saying "oversteering has nothign to do with speed?"

FYI, Drifting is actually "some sort of understeer".

Excessive speed will cause understeer. Try it when you enter into a corner.

Drifting is a controlled over-steering situation.

Oversteer happen only when rear wheels slip angle is greater than front wheels.
"losing traction" is not technical correct.

You are telling everyone what is oversteer. It is obvious the rear wheels slip angle has to be greater than the front. But what causes the rear to have greater slip angle if not for a lost of traction!!????

Lifting throttle cause weight to shift to front (not all), and making rear wheels contact patch smaller, thus increasing slip angle, and result in oversteer.

Cheers

Whether the contact patch is smaller will be debatable (short of saying you are wrong ), but for sure there is less contact pressure between the tire surface and the tarmac which translates into lesser grip or traction!!

Now let me elaborate about contact patch and why you missed the mark.

Contact patch area is not affected by the weight shift to the front but rather the centrifugal force that causes a change in the tire's camber! The tire would have maximum grip when it is perfectly perpendicular to the tarmac. In all cases, cars have negative camber because the centrifugal force will change the camber to zero (maximum grip) when cornering (depending on the speed and when that happens, you are at the limit) before you start to lose control of your car.

That is where thicker anti roll comes into play (to resist the camber change), well that is another story.

Cheers

 

[astroboy]

I have also experienced the "throttle-off oversteer" aka "lift-off oversteer" with my current set up.. kind of cool. It happened at one of the corner after passing Tropicana before reaching Menara Lien Hoe. It was a wet day too, I wasn't even speeding. I take the corner and the car in front slows down to turn into Menara Lien Hoe. I turn and lift throttle. The fish tail happened. It was a mild one but its EXCITING!!!

I do agree with bundy, oversteer has nothing to do with speed and have everything to do with chassis balance or traction variance between front and rear wheel. Normal JDM sedans are set up to understeer, so no matter how fast u take corner, the car will only screech and understeer, not oversteer. Until u lift off, CG transfered to the front, rear contact patch or traction or weight or grip reduce, oversteer will prevail in this situation. So its not speed.

For a perfect balance car powering through corner at high speed, all 4 wheels skid together and that's not called under or over steer.

 

[danc]

Guys listen to President, he really knows what his talking about.

 

[astroboy]

Those who think oversteer is caused by excessive speed watches too much movie and I was one of them..