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"? :?


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]

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]

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! :blink:

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

Best regards david

[Boxbrownie]

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.


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]

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]

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

[Boxbrownie]

That quote BTW is not referreing to "bump steer" in the true sense of the word, it is referring to wheel fight and the tendancy of power steering to mask the effects of fight from wider wheels and tyres.
Bump steer is the effective shortening or lengthening of one or both of the steering links caused by usually vertical movement of the wheel resulting in the wheel turning slightly, this causes "bump steer".

[mickd]

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
Can't agree with you, you have your opinion, I have mine, that's OK. Ask anyone with an early 911 with manual steering, and they will tell you the same. It's like a go-cart. Sure, a stock 318ti doesn't have much bump steer since it is a street oriented suspension. I guess you have never driven hard through a corner and hit an irregularity in an early 911. These problems others are mentioning, car having a mind of it's own in a straight line, is tramlining.

[mickd]

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
And tell Porsche AG they have a bad suspension design, the company that won LeMans more than any other manufacturer, 16 times from 1970-1998.

[Boxbrownie]

Can't agree with you, you have your opinion, I have mine, that's OK. Ask anyone with an early 911 with manual steering, and they will tell you the same. It's like a go-cart. Sure, a stock 318ti doesn't have much bump steer since it is a street oriented suspension. I guess you have never driven hard through a corner and hit an irregularity in an early 911. These problems others are mentioning, car having a mind of it's own in a straight line, is tramlining.

No not a 911.....last time I drove one of those it felt like the clutch was an on/off switch and sounded like there was a sewing machine in the "trunk" :icon_poke

But while setting up a Brabham BT21 in the early seventies at Brands Hatch I had the opportunity to squirt a few laps in a 914/6, that handled absolutely fine, but of course the engine was in the correct place on that one :evil_lau:

Seriously though, I was just trying to clear up the definition of "bump steer" as it can happen on turning or straight line, you can even induce it by vertical movement of the front of a vehicle while stationary (if that vehicle has bump steer geometry), you can measure it with laser alignment doing this.

A lot of symptoms of bad geometry/toe in-out misalignment/worn bushes or ball joints or even over size tyres can be interpreted and are called "bump steer", I was just trying to point out that in the true sense of the terminology it could be and on modern vehicles probably is some other malady.

BTW for the past 27 years I have worked in the reseach and engineering centre or one of the biggest vehicle manufacturers in the world and get heavily involved in the design development and testing of every aspect of vehicle engineering, honestly I do know what bump steer is... :)

Anyway .....back to the original poster.......as has been said before get your alignment checked properly and a good point was made about worn bushes and joints, the lower outer ball joint is quite prone to wear on the E36 and should be checked by "squeezing" the joint top to bottom with large grips while no load is on the joint. But its more than likely down to just the larger tyres fighting each other more for grip on the road surface, not alot you can do apart from play with the castor/camber settings using offset top mounts and A arm bushes, this can give you better directional stability and often negates the effect of the wider tyres. I have read here that M3 bushes have the required settings (which would make sense), but you need to talk with somebody who has experience of fitting them already I think, not just theorising like me! :biggrin:

best regards David

[Boxbrownie]

One point....I didnt say Porshe had bump steer, you did :) If you look at Dennis Adler's quote you inserted he doesnt mention bump steer either, just wheel fight....

quote

""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."

Which is exactly what I said happens with power steering, it tends to mask/absorb any wheel fight in the system.

I would never dream of accusing Porshe of having lousy handling, Derek Bell would pummel me! LOL

But I would say Porshe has "characterful" handling :biggrin:

Now I have to work......this is all real good fun isnt it? :2gun:

Best regards David

[mickd]

There is alot of info on the net that talks about bump steer and how steering is affected by suspension geometry, that goes without sayinging. When I was first exposed to road racing probably 30 years ago most of the racers referred to "bump steer" when the steering jerked your hand on rough surfaces through the corner. Two other guys I knew raced early 911's ('72 and '73) and talked about these tendancies. So that is why I referred to this as bump steer. I think your definition is a more recent one, now that cars better engineered. And it takes a very good driver to take an early 911 to the limit. A feeling you can get in no other vehicle.

[Boxbrownie]

But is that a feeling you would want with any other vehicle? :evil_lau:


I actually learnt about bump steer and a lot of other stuff from the brabham engineer who sold us the chassis, they were so helpfull (and cheap compared to scholar et all) considering it was a secondhand chassis......

The odd thing is over here on this side of the pond we would always refer to "wheel fight" or "chatter", where as "bump steer" was a well known and engineered out (usually) problem that occured only on much older vehicles (and this was in the 70's), it was just another cock up that could be easily made by home builders along with torque steer, axle tramp and all the other problems that should by now be designed completely out of modern systems.

Anyway whatever we call it, lets hope the problem gets solved by a good alignment engineer?

Best regards David

[bluebastion]

mmmm.... my pizza is good.

[mickd]

But is that a feeling you would want with any other vehicle? :evil_lau:
I wouldn't want to drive it everyday, but as a weekend car it's great fun. The newer 911's are better everyday cars in every sense. It's just the elemental feel of all the controls that makes early 911's so endearing to me. I like the 'ti so much better as an everyday car. I would be tempted to give up the 911 for an E36 M3 or an S50 conversion on the ti. I know the ti would be as quick straight line, and handle much better.

[KdCass]

I read most of the LONG forum hehe..

One thing I've gatherd is the gents having the "bump steer" problems all recently put on 17s.

I know the sticker on the inside of my door says not to use any wheel over 16in. I know there are tons of gus with 17-18s, do they all have this problem?

Maybe the heavier wheel changes the umm err geometry of the suspension, or the outer diameter of the wheel is getting larger. Or BMW might just say 16s or less to keep from boggin the little motor down.


Just my $.02

Remeber drunk drivers:
Swerve to the right

-Dave

[Boxbrownie]

I have 17" on mine OEM wheels with correct size tyres 225/45 Mich PS2 (front) & PS1 (rear) and standard ride height and I have no problems with steering tug straight ahead or fight through corners. No doubt I am sure that if I do lower the vehicle the resultant change in geometry will induce some characteristic not present now.
In fact I love the handling of this car, it is so "chuckable" and the michelins really do stick like sh*t to a blanket.......

Dave........stay with it......read it all......LOL

Ah yes Dave....the OEM 17" wheels and tires (I give in to your side of the pond there) are actually lighter than the 15" steel set I took off.......should be really, a lot less tyre (doh! couldnt keep the accent up) and more "air" within the wheel!

The diameter is spot on give or take a few mm...

I really do like to keep everything as mother BMW intended don't I? LOL

Best regards David

[KdCass]

I read most of the LONG forum hehe..

One thing I've gatherd is the gents having the "bump steer" problems all recently put on 17s.

I know the sticker on the inside of my door says not to use any wheel over 16in. I know there are tons of gus with 17-18s, do they all have this problem?

Maybe the heavier wheel changes the umm err geometry of the suspension, or the outer diameter of the wheel is getting larger. Or BMW might just say 16s or less to keep from boggin the little motor down.


Just my $.02

Remeber drunk drivers:
Swerve to the right

-Dave

[bmwpwr]

I read most of the LONG forum hehe..

One thing I've gatherd is the gents having the "bump steer" problems all recently put on 17s.

I know the sticker on the inside of my door says not to use any wheel over 16in. I know there are tons of gus with 17-18s, do they all have this problem?

Maybe the heavier wheel changes the umm err geometry of the suspension, or the outer diameter of the wheel is getting larger. Or BMW might just say 16s or less to keep from boggin the little motor down.


Just my $.02

Remeber drunk drivers:
Swerve to the right

-Dave

I still have the stock 16" wheels and have the wheel fight/tug problem. I have somewhat discounted that the car has a bump steer unless the geometry is not correct on the sport packages due to the lower springs. The problem most likely lies somewhere else.

I need to make this car "stick like sh*t to a blanket......." as boxbrownie says since I dont have the power to keep up with other cars on the straights. I want to eat them up in the corners.

[BMWVW]

I run my car with 17in 225/55's in the summer and 15in snow tires in the winter (as much as I hate to). The summer tires definitely have a tendancy to follow irregularities on the road, but for the rest handles very well.

A few months ago I started to get problems were the car would not track properly around corners and any bumps would cause it to go more off track. This was with the winter tires which are normally more forgiving.

Turned out the rear shocks and bushings were worn out. Expensive repair, but it nows drives like it used to.

Probably a little different from what you are experiencing, but just thought I would throw that out there just in case.
Cheers,
Paul.

[Boxbrownie]

Its a good point BMWVW.....people often overlook the fact that a worn rear end component can induce the effects of something feeling amiss at the front end!

Best regards David

[dodj]

my 96 sport came stock with 17" i have no problems goes straight as an arrow over bumps.

the car will follow deviations in the road sometimes but nothing that feels dangerous.