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BMW 3-Series (E90 E92) Forum > E90 / E92 / E93 3-series Technical Forums > All-Wheel-Drive (Xi / xDrive) Talk > Issues



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      03-26-2013, 03:24 PM   #1
practice89
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Issues

Didn't know where to post it but since I have a XI, decided to post here.

When i drive on some uneven roads, it feels like the car looses grip for a second and then regains grip. So it feels like I lose control of the car and then regain it a second after. it is kind of hard to explain....

The only modification I have on the car is KW V1 coilovers.

Anyone have any idea what can cause this?


Thanks in advance.
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      03-26-2013, 03:47 PM   #2
BCeagle08
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I assume this happens more when you are going around a curve than when you are driving straight, but it can happen while driving straight as well, although to a lesser extent.


Your high speed compression is too high, it causes an effect known to racecar drivers are "skating."

Essentially what is happening is the bumps in the road are compressing your springs faster than the shocks will allow. The extra energy is transferred to your chassis instead of being absorbed by the springs. This causes the car to bounce up and off the road for a split second. In this split second, the tires lose grip with the road (or have less grip than they did before). Your tires quickly regain grip as the spring rebounds and the energy from the bump is dissipated.

This creates the feeling that you described. The only solution would be getting a softer shock setup. In a perfect world, you would have adjustable shocks which have High and low speed compression settings as well as rebound settings. Racecars have these types of settings, your KW V1s do not. They are a jack of all trade cheap shock made to handle normal road use.

I would not worry about it, there is nothing wrong with your car. It happens to all cars. You probably just notice it more now that you have coilovers. Just keep that feeling in mind when you decide to try and push your car to its limits on the street. Imagine being at the edge of grip and then having your car lose grip because of the skating effect. Be ready to change your underwear after that one
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      03-26-2013, 04:45 PM   #3
chesterfan1230
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Sup bro,

The above poster sounds spot on. I'd also check tire wear.

Going around turns under high compression causes the wheel to camber out (not actually changing the camber) but just angling outwards. If you have poorly worn tires it'll slide a bit.

But don't you have new-ish tires too?
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      03-26-2013, 05:16 PM   #4
practice89
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Quote:
Originally Posted by BCeagle08 View Post
I assume this happens more when you are going around a curve than when you are driving straight, but it can happen while driving straight as well, although to a lesser extent.


Your high speed compression is too high, it causes an effect known to racecar drivers are "skating."

Essentially what is happening is the bumps in the road are compressing your springs faster than the shocks will allow. The extra energy is transferred to your chassis instead of being absorbed by the springs. This causes the car to bounce up and off the road for a split second. In this split second, the tires lose grip with the road (or have less grip than they did before). Your tires quickly regain grip as the spring rebounds and the energy from the bump is dissipated.

This creates the feeling that you described. The only solution would be getting a softer shock setup. In a perfect world, you would have adjustable shocks which have High and low speed compression settings as well as rebound settings. Racecars have these types of settings, your KW V1s do not. They are a jack of all trade cheap shock made to handle normal road use.

I would not worry about it, there is nothing wrong with your car. It happens to all cars. You probably just notice it more now that you have coilovers. Just keep that feeling in mind when you decide to try and push your car to its limits on the street. Imagine being at the edge of grip and then having your car lose grip because of the skating effect. Be ready to change your underwear after that one

sounds like a very reasonable explanation lol.

any other KW V1 owners having this issue??
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      03-26-2013, 05:16 PM   #5
practice89
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Quote:
Originally Posted by chesterfan1230 View Post
Sup bro,

The above poster sounds spot on. I'd also check tire wear.

Going around turns under high compression causes the wheel to camber out (not actually changing the camber) but just angling outwards. If you have poorly worn tires it'll slide a bit.

But don't you have new-ish tires too?
tires are pretty worn out, guessing it's adding to this skating effect??
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