Bump Steer

[bmwpwr]

Does anyone else have noticeable bump steer on their sport package ti's? My active package ti has none. My dads M3 has none. My new sport has a ton of it. This seems pretty uncharacteristic of a BMW suspension, at least the ones I have driven. This car is like driving a ford mustang with a live rearend. Im interested to see what it does on the road course this weekend.

[Billan]

My 98 sport has a lot of bump steer. It is much worse with my 18's on though. I am getting new suspension installed this weekend (H&R's with Koni adjustables) so I hope it makes it better (Worn shocks etc). Try getting your car aligned, it seems to be a lots worse when I need an alignment (Toe in is screwed up).

[L84THSKY]

Define "Bump Steer"?

Originally Posted by bmwpwr

Does anyone else have noticeable bump steer on their sport package ti's? My active package ti has none. My dads M3 has none. My new sport has a ton of it. This seems pretty uncharacteristic of a BMW suspension, at least the ones I have driven. This car is like driving a ford mustang with a live rearend. Im interested to see what it does on the road course this weekend.

[Boxbrownie]

Bump steer is due to incorrect geometry of the suspension, either caused by bad design or wrongly fitted/mismatched components....I have never heard of a BMW having noticable bump steer......are you sure that what your feeling and not just tramlining from a wider wheel/tyre combination?

Best regards david

[Billan]

Originally Posted by L84THSKY

Define "Bump Steer"?

The car will "Bump off" when hitting small bumps in the road especially at high speeds. This will cause you to have to "work" to keep the car straight. This is usually a problem with the front toe settings. I will be getting an alignment after my suspension install so my problem should be corrected. This occurs all the time after the winter with the wonderfull NE roads we have around here.

[Boxbrownie]

Ok.....this is not bump steer in the true sense....just to much toe out probably, each front wheel is literally fighting for the straight line!
Bump steer is the result of wheel deflection causing the effective shortening/lengthening of the steering arm geometry, thus causing that wheel to try to steer independentely of steering wheel input. Best explaination I can muster at this time of night LOL.

best regards David

[bmwpwr]

Originally Posted by Boxbrownie

Bump steer is due to incorrect geometry of the suspension, either caused by bad design or wrongly fitted/mismatched components....I have never heard of a BMW having noticable bump steer......are you sure that what your feeling and not just tramlining from a wider wheel/tyre combination?

Best regards david

Im pretty sure what Im feeling is bump steer. The car is new to me and I suspect the alignment may be off. Hopefully, I can cure it with a little toe out on the front and rear. Ive driven BMW's with wider wheels and tires than what ive got and never experienced anything close to bump steer in a BMW.

Does anyone have any numbers for an "aggressive" alignment settings?

[L84THSKY]

That sounds like what is happening on my car. I just went from 205/60/15 to 235/45/17. The car has a mind of it's own, when it finds a groove in the road. Kinda like having a 200lb dog on a leash, and it just saw a cat!

Originally Posted by Boxbrownie

......are you sure that what your feeling and not just tramlining from a wider wheel/tyre combination?

Best regards david

[Boxbrownie]

Originally Posted by bmwpwr

Im pretty sure what Im feeling is bump steer. The car is new to me and I suspect the alignment may be off. Hopefully, I can cure it with a little toe out on the front and rear. Ive driven BMW's with wider wheels and tires than what ive got and never experienced anything close to bump steer in a BMW.

Does anyone have any numbers for an "aggressive" alignment settings?

Misalignment due to incorrect toe settings will not cause bumpsteer on a system that has none inherently, I am sure you will find it is just alignment and wider wheels tyres causing the problem, being rear wheel drive these cars need slight toe in or on a perfect system parallel settings ( solid bushes ie track/race ).

Best start with a full alignment check, and make sure the guys who are doing it know how to set it up correctly! Find an enthusiastic vendor!

Best regards David

[mickd]

Bump steer usually occurs when the steering is heavily loaded to one side or another, like when you are cornering hard, and the tire hits an irregularity in the road causing the steering wheel to jerk a bit in your hand. I think most sport oriented suspensions have it to some degree. Cars with no assist in the steering are worse, it seems the assist dampens it a bit. Certain tires are worse than others for this, I would think lower profile tires are worse because they don't have as much "give". That's why the setup of the suspension is really critical with super low profile tires, the suspension has to do more dampening since the tire can't when you have rubber bands. My 911 is bad for bump steer since early 911's had no assist up until the 1989 Carrera 4, my '88 coupe doesn't have it. Not a bad thing, just a trait you learn to live with, early 911's just have a more direct feel, like a competition car. I just found this quote in one of my 911 books, Porsche 911 Road Cars, by Dennis Adler, talking about the '89 Carrera 4: "One Improvement that almost goes unoticed is Porsche's power assisted steering, which manages to enhance the cars handling without taking away any of that wonderful feedback that 911's have always provided. What has been erased from the steering is the tendancy for the wheel to be wrenched from your hands when encountering a bump in the middle of a turn. You no longer have to manhandle the car in corners. The power assist handles the counterforce, you handle the car." I never really thought the ti was that bad for bump steer, but it does exist, to some degree, in any car with a more sporting nature and suspension. Just much worse on a car with manual steering.

[BMWDRIFTER]

what you are probably feeling is worn or failed control arm bushings in the front, loose ball joints, worn tie rod ends, or rear subframe mounts that have failed. Almost every car that is massed produced has some amount of bump steer as mentioned. what you are feeling is a part that is moving from one extreme to the other. bad control arm bushing on the lower control arms will give this feeling. you can see the wheel actually move about 1" back and forth when you hit the brakes at low speed. the rear subframe mounts if bad enough can make the back end want to change lanes when getting on and off the gas. Get the entire suspension checked really good.

[97Hellrot318ti]

This sounds exactly like what I have been experiencing. I've definitely noticed it since tossing on my 17"s... You hit a minor irregularity in the road, especially when the wheels are already turned, and they just want to keep going. Nothing dangerous really, always seems to happen when I'm slowing down to change into a left-turn lane or something like that. I also am in some need of an alignment so hopefully that will correct it.

[L84THSKY]

All I can say is.....when I had my 205/60/15's on the car, this pulling of the car never happened. I put on the 235/45/17's just two weeks ago, and the problem is apparent. I had a wheel alignment done, at the same time.

I agree with boxbrownie that wider tires make this situation occur in alot of cases.

Originally Posted by 97Hellrot318ti

This sounds exactly like what I have been experiencing. I've definitely noticed it since tossing on my 17"s... You hit a minor irregularity in the road, especially when the wheels are already turned, and they just want to keep going. Nothing dangerous really, always seems to happen when I'm slowing down to change into a left-turn lane or something like that. I also am in some need of an alignment so hopefully that will correct it.

[bmwpwr]

Originally Posted by Boxbrownie

Misalignment due to incorrect toe settings will not cause bumpsteer on a system that has none inherently, I am sure you will find it is just alignment and wider wheels tyres causing the problem, being rear wheel drive these cars need slight toe in or on a perfect system parallel settings ( solid bushes ie track/race ).

Best start with a full alignment check, and make sure the guys who are doing it know how to set it up correctly! Find an enthusiastic vendor!

Best regards David

I agree that a misalignment is not the cause of the bump steer. Your definition above was good. I was hoping that a good alignment would help hide the problem. I am not familiar with setting these 318ti for the track so any help is appreciated. They are a little more complicated than my spridget race car! Are you sure I want a little toe in? Im not sure I want the car to turn in any harder than it does already.

[Boxbrownie]

Originally Posted by mickd

Bump steer usually occurs when the steering is heavily loaded to one side or another, like when you are cornering hard, and the tire hits an irregularity in the road causing the steering wheel to jerk a bit in your hand. I think most sport oriented suspensions have it to some degree. Cars with no assist in the steering are worse, it seems the assist dampens it a bit. Certain tires are worse than others for this, I would think lower profile tires are worse because they don't have as much "give". That's why the setup of the suspension is really critical with super low profile tires, the suspension has to do more dampening since the tire can't when you have rubber bands. My 911 is bad for bump steer since early 911's had no assist up until the 1989 Carrera 4, my '88 coupe doesn't have it. Not a bad thing, just a trait you learn to live with, early 911's just have a more direct feel, like a competition car. I just found this quote in one of my 911 books, Porsche 911 Road Cars, by Dennis Adler, talking about the '89 Carrera 4: "One Improvement that almost goes unoticed is Porsche's power assisted steering, which manages to enhance the cars handling without taking away any of that wonderful feedback that 911's have always provided. What has been erased from the steering is the tendancy for the wheel to be wrenched from your hands when encountering a bump in the middle of a turn. You no longer have to manhandle the car in corners. The power assist handles the counterforce, you handle the car." I never really thought the ti was that bad for bump steer, but it does exist, to some degree, in any car with a more sporting nature and suspension. Just much worse on a car with manual steering.

Sorry, but bump steer is purely a result of bad suspension geometry design.

If the geometry of the vehicle has bump steer designed out completely (which most have now days) no amount of lateral or vertical force will induce it.....iza simple geometry, honest......

best regards David