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Discussion Starter #1
What the hell is oversteer and understeer ??? I've been reading a lot of threads recently and I keep coming across talk about oversteer and understeer... is this literally or figuretively ? And why do so many member replace the rear sway bar and not the front one ? I have the ACS DFC suspension, will thicker sway bars help ? Questions coming from a newbie.

Thanks in advance,
Edgar
 

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Edger,

There are no dumb questions. Welcome to the board.

Both terms have to do with car control dynamics, and here's my feeble attempt to answer your questions:

Understeer: The car tends to go straight even when you are turning the steering wheel, thus 'under'(insufficient)-steer. This is mostly due to FRONT tires loosing traction in corners. When you go into a corner too hot, the car carries forward momentum, and you feel the car's front end plowing straight even though you are turning the wheel. To compensate, you need more weight, thus traction, on the front tires. Lifting the throttle, or light braking, shifts weight to the front tires. A natural reaction when you think you are loosing it.

Oversteer: The tail end spins out during cornering, the car turns/spins more than your steering input, thus 'over'(too much)-steer. This is because your rear tires are loosing traction. To compensate, you need more weight/traction on the rear tires. Believe it or not, adding throttle at this point actually shifts weight to the rear tires, and will help. This is totally OPPOSITE to instincts. You think you want to slow down when you spin. Slowing down at this point shifts MORE weight to the front, and you will spin for sure.

That is why most cars come with understeer bias from the factory. It is more safe as the slow-down instinct actually helps you out.

Camber plates are a good remedy. When you corner hard, a zero-camber car will roll the tires onto it's edges, reducing contact patch, and thus traction. With the proper negative camber set up, your tires roll more on edges in straight runs, but hard corners will roll the tires onto the full contact patch, increasing traction, and just as important, contact patch area, as you power out of corners.

Another remedy is to run wider tires up-front, and many board members do that. The reason is obvious, wider tires=more contact patch area=more traction in corners= less understeer.

Sway bars. The factory sway bar is deliberately under-sized to under-steer the car. Members who like to have more neutual handling up-size (stiffen) the rear bar to be compatible with the front bar.

If you are not a seasoned driver skilled at judging corner entrance and exit speeds, I'd say leave some understeer in your car. It is safer. Of course, the DSC will bail you out if called on as well.

Hope this helps.

CP
 

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Well Done!


Regards,


Marion
chunpng said:
Edger,

There are no dumb questions. Welcome to the board.

Both terms have to do with car control dynamics, and here's my feeble attempt to answer your questions:

Understeer: The car tends to go straight even when you are turning the steering wheel, thus 'under'(insufficient)-steer. This is mostly due to FRONT tires loosing traction in corners. When you go into a corner too hot, the car carries forward momentum, and you feel the car's front end plowing straight even though you are turning the wheel. To compensate, you need more weight, thus traction, on the front tires. Lifting the throttle, or light braking, shifts weight to the front tires. A natural reaction when you think you are loosing it.

Oversteer: The tail end spins out during cornering, the car turns/spins more than your steering input, thus 'over'(too much)-steer. This is because your rear tires are loosing traction. To compensate, you need more weight/traction on the rear tires. Believe it or not, adding throttle at this point actually shifts weight to the rear tires, and will help. This is totally OPPOSITE to instincts. You think you want to slow down when you spin. Slowing down at this point shifts MORE weight to the front, and you will spin for sure.

That is why most cars come with understeer bias from the factory. It is more safe as the slow-down instinct actually helps you out.

Camber plates are a good remedy. When you corner hard, a zero-camber car will roll the tires onto it's edges, reducing contact patch, and thus traction. With the proper negative camber set up, your tires roll more on edges in straight runs, but hard corners will roll the tires onto the full contact patch, increasing traction, and just as important, contact patch area, as you power out of corners.

Another remedy is to run wider tires up-front, and many board members do that. The reason is obvious, wider tires=more contact patch area=more traction in corners= less understeer.

Sway bars. The factory sway bar is deliberately under-sized to under-steer the car. Members who like to have more neutual handling up-size (stiffen) the rear bar to be compatible with the front bar.

If you are not a seasoned driver skilled at judging corner entrance and exit speeds, I'd say leave some understeer in your car. It is safer. Of course, the DSC will bail you out if called on as well.

Hope this helps.

CP
 

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Great explanation! I'll be putting this in my favorites.
 

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Discussion Starter #6
Chunpng,

Oooh, there is a name for that ! That is a great explaination. Now I know what to call it since I've experienced both under and oversteer. I thought that problem was solely related to the tires... Pirelli P Zero Rosso's. I would imagine the tires have something to do with it, right ? I'm need new tires, so are these good enough or should I go with Bridgestone SO-3's ? Also, I'm not a seasoned driver so I should probably stay with a little understeer; hence, I could replace BOTH rear and front sway bars for better handling, right ?

Again, thank you.

Edgar



chunpng said:
Edger,

There are no dumb questions. Welcome to the board.

Both terms have to do with car control dynamics, and here's my feeble attempt to answer your questions:

Understeer: The car tends to go straight even when you are turning the steering wheel, thus 'under'(insufficient)-steer. This is mostly due to FRONT tires loosing traction in corners. When you go into a corner too hot, the car carries forward momentum, and you feel the car's front end plowing straight even though you are turning the wheel. To compensate, you need more weight, thus traction, on the front tires. Lifting the throttle, or light braking, shifts weight to the front tires. A natural reaction when you think you are loosing it.

Oversteer: The tail end spins out during cornering, the car turns/spins more than your steering input, thus 'over'(too much)-steer. This is because your rear tires are loosing traction. To compensate, you need more weight/traction on the rear tires. Believe it or not, adding throttle at this point actually shifts weight to the rear tires, and will help. This is totally OPPOSITE to instincts. You think you want to slow down when you spin. Slowing down at this point shifts MORE weight to the front, and you will spin for sure.

That is why most cars come with understeer bias from the factory. It is more safe as the slow-down instinct actually helps you out.

Camber plates are a good remedy. When you corner hard, a zero-camber car will roll the tires onto it's edges, reducing contact patch, and thus traction. With the proper negative camber set up, your tires roll more on edges in straight runs, but hard corners will roll the tires onto the full contact patch, increasing traction, and just as important, contact patch area, as you power out of corners.

Another remedy is to run wider tires up-front, and many board members do that. The reason is obvious, wider tires=more contact patch area=more traction in corners= less understeer.

Sway bars. The factory sway bar is deliberately under-sized to under-steer the car. Members who like to have more neutual handling up-size (stiffen) the rear bar to be compatible with the front bar.

If you are not a seasoned driver skilled at judging corner entrance and exit speeds, I'd say leave some understeer in your car. It is safer. Of course, the DSC will bail you out if called on as well.

Hope this helps.

CP
 

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charronegro said:
Chunpng,

Oooh, there is a name for that ! That is a great explaination. Now I know what to call it since I've experienced both under and oversteer. I thought that problem was solely related to the tires... Pirelli P Zero Rosso's. I would imagine the tires have something to do with it, right ? I'm need new tires, so are these good enough or should I go with Bridgestone SO-3's ? Also, I'm not a seasoned driver so I should probably stay with a little understeer; hence, I could replace BOTH rear and front sway bars for better handling, right ?

Again, thank you.

Edgar


Folks,

Thanks for the kind words. I'm by no means an expert in this area. If Redshift, or KKelly (DE instructors) can chime in, they'd shed much better light on the subject.

Edger,

Under and oversteer can be made more sensitive by tire conditions, both in the tire pressure, and tread conditions.
Over-inflation reduces contact patch, thus the car will reach it's tire adhersion limits sooner. Tread conditions affect tire behavior on different pavement surfaces. Bald tires actually have more traction on dry surfaces, but are downright dangerous on wet pavements. That's why in car control clinics, we do skid pad runs on wet concrete pads.

If you need new tires, you should get them for safety, less so for at the limit driving conditions. As to which tire to get. I think Pirelli Rossos and Bridgestone SO3s are great tires. I have heard that S02 As or Ribs are even better than S03s. I have Yokohama AVS on mine and I love those as well. You have the ACS DFC suspension. That's a great set-up. Your car should handle much better than most M5s on the road.

BMWCCA has great car-control-clinic events. You will learn how to corner at the limit, and how to recover from spins (both under and over-steer conditions). They are also pre-requisite for further BMWCCA Driving Events. If you have not attened the CCCs, I highly recommed them.

Good luck.

CP
 

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Great explanation chunpng. Why dont we throw power sliding while are at it. I know thats its when the car drifts on 4 wheels but i just wanted you to give your fine explaining for those who dont know what it means :thumbsup:
 

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Great writeup Pong, but I'll disagree with you on one point. When one is oversteering in a street car, the best way out of it is to countersteer and slowly let off the gas. In a car with a lot of grip, ie a F1 car, then getting on the gas might transfer some weight to the rear tires and help. But in a street car with relativly low grip, adding gas when you are tail out will usually only send the back out worse, especially if we are talking about a 400hp beast. I've tried that method many times, and in may different cars, and I am yet to see it work. Power applications during oversteer in street cars make it worse.
Abdulla powersliding is a term that gets thrown around for many different typed of drifts. A power on drift means you are using extra power to spin the back tires and then you hold the back end out with your countersteer. It's a balance of hands and feet, as your throttle setting will dicate how much you countersteer, and your speed factors in there too. Feel what the wheel is telling you, as I have found that if the wheel is fighting you, you have a wrong input in.
4 wheel drifting means you have the car out so far that even the front tires with full lock countersteer have a slip angle too. Really hard to do, and requires more control than a power on slide. Fun to do with AWD, as a lot of the time in those cars if you get them out you can get it back, even with insane drift angles.
:cheers:
 

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BmwNut said:
4 wheel drifting means you have the car out so far that even the front tires with full lock countersteer have a slip angle too. Really hard to do, and requires more control than a power on slide. Fun to do with AWD, as a lot of the time in those cars if you get them out you can get it back, even with insane drift angles.
:cheers:
Yeah try driving in first gear @25 mp/h and then nailing it in a lefter with 12 screaming cylinders behind your ears. Result was that it threw me sideways drifting on all four tires with me hopelessly looking at the fast coming pavmement and waiting for her to grip :eek:

Never have i again messed with her in such a strong tight curve. There were only 2 lanes turning to the left from the lights
 

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Here's a strange theiry i came across!

In a front wheel drive vehicle, the chances of over steer are made greater by accelerating in a turn and then letting go of the throttle! The rear end will automatically go sideways!
 

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That is a characteristic of rear drive as well. The throttle lift decreases rear grip and increases front grip. The front then acts like a pivot point as the rear rotates around. At a track I go to, a short right after a long straight has a bump. This unsettles the rear end at 100+ mph. If you lift at that point, the car will try to come around. A misunderstsnding with an instructor caused me to lift one time. The back end started to drift. I then had to counter steer and get the car under control just in time for a sharp left. There is at least one Porsche at every event that does a 180 there.
 

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Richard in NC said:
That is a characteristic of rear drive as well. The throttle lift decreases rear grip and increases front grip. The front then acts like a pivot point as the rear rotates around. At a track I go to, a short right after a long straight has a bump. This unsettles the rear end at 100+ mph. If you lift at that point, the car will try to come around. A misunderstsnding with an instructor caused me to lift one time. The back end started to drift. I then had to counter steer and get the car under control just in time for a sharp left. There is at least one Porsche at every event that does a 180 there.
Richard, you wouldn't be referring to *cough* DAN *cough*? 911's are famous for their tendency to end-swap. Also, adding to what Richard said, I noticed you can very easily drive with the throttle in the M5 at some tracks, eg. Roebling, has a long sweeper, you enter at 80+, and stay in the throttle, if it starts to push out, just roll out of the throttle some, the weight shifts, and the front will come back to you, so you can steer again. Balancing the car with oversteer, using the throttle is a good technique, but one that requires a few 'agriculture experiences' for you to find the limits.
 

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chunpng said:
Oversteer: ...adding throttle at this point actually shifts weight to the rear tires, and will help. ...
CP
Pong,

Wouldn't it be true, however, that if the oversteer (lack of traction to the rear wheels) was caused by too much power (starting to spin the wheels) the only remedy is to countersteer and back off the throttle a **small** amount?

It is very easy (with DSC off) to spin those rear wheels with our Beastly torque!

Paul

P.S. - Pong I'm glad you are okay and mourn your loss.
 

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pkarmouche said:
Pong,

Wouldn't it be true, however, that if the oversteer (lack of traction to the rear wheels) was caused by too much power (starting to spin the wheels) the only remedy is to countersteer and back off the throttle a **small** amount?

It is very easy (with DSC off) to spin those rear wheels with our Beastly torque!

Paul

P.S. - Pong I'm glad you are okay and mourn your loss.
Paul,

Thanks for the kind wishes. I'm doing well considering the circumstances.

Folks,

You raised some great points. When I wrote my blurb above, that is not meant to cover ALL situations, as the handling characteristics of front-engine/rear-engine, or front-drive/rear-drive cars are quite different. I meant that as a general observation/answer to under steer and over steer.

Yes, a rear engine car that puts down too much power in the rear wheels during turns (ala older Porsche turbo models) can cause the car to over steer, and backing off the throttle a 'hair' while counter steering is the way to save it. Even then, one has to be judicious with the throttle, because a sudden, full lifting of the right foot had caused many Porsches to spin. Thus the adage: NEVER LIFT, in the Porsche world. I thought about describing this situation before, but thought that could be confusing, so I skipped it.

CP
 

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I thought that problem was solely related to the tires... Pirelli P Zero Rosso's. I would imagine the tires have something to do with it, right ? I'm need new tires, so are these good enough or should I go with Bridgestone SO-3's ? Also, I'm not a seasoned driver so I should probably stay with a little understeer; hence, I could replace BOTH rear and front sway bars for better handling, right ?
Unfortunately, it's more complex than that. First, tires do make a difference. If you swap out all four at once (recommended so that they are all the same brand/model) and keep everything else the same, different tires have different characteristics, and so a car that used to understeer slightly could now be more neutral or even oversteer. While large differences are rare based on tire brand changes alone, it can happen, even though one would expect that going to "better" tires would simply increase the grip the same way w/o affecting the handling balance. Also, cars vary from each other depending on exactly how well the springs match, how worn the shocks are, etc. This helps explain why, for example, I and several others who have upgraded to a Dinan adjustable rear sway bar have found the stiffest setting to have too much oversteer for street (or track) driving, while others, possibly running a different tire brand, find it just right.

Anyway, you should definitely stay with handling balance towards understeer. I recommend that for any street driven car, regardless of driver experience. In emergency situations on the street, you will want to be able to bleed off speed to reduce the chances of damage or injury. Powering thru can work for the track, but not when you're trying to avoid accidents on the highway. At least that's my opinion.

Going to stiffer front and rear bars won't necessarily make your car handle better. They will make the car ride flatter in turns with less body roll, but you may be going slower because the added stiffness may give the car less traction, especially if the road is bumpy. Most people have found that going to a larger front bar on the M5 is not necessary. Rather, if you want to dial out some of the understeer but not all of it, the better choice (at least at first) is to try going to a slightly bigger adjustable rear bar, like the Dinan bar. Start with the softest setting, as even that will reduce understeer over the stock bar. Be careful going up from there, as you won't really know if you've gone too far until you've gone too far. I run rear wheel/tire sizes all around, and because of the added grip of the front tires, have left my Dinan bar at its softest setting to make sure I'm working the front tires good and hard. I found that moving up the rear bar in stiffness with my particular combination actually gave me less grip and a bit too much oversteer for my tastes for street driving. (It was reallly exciting driving in the rain on the middle setting!) If I had stock tire sizes in front, however, I'd probably be using the middle setting.
 
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