Twitchy steering 35is - Update now FIXED!

[Kryton]

My 35iS is rock solid at speed and runs true and straight.

Same as my old 35iS, no problem whatsoever

[jelmok]

Ouch. I'd start with the basics. Tyre inflation, alignment check, tyre check. Next thing to check is for slightly damaged or bent suspension parts.

Thanks for that. Been out and checked the tyres - I assumed the dealer would have done this - only owned the car for nearly two weeks. They weren't too far off - the rears were down a little at 2.7 bar instead of 2.9 and the front were at 2.2 and 2.3 - now at 2.4. Are these the pressures that you guys suggest using? I am on the 19inch 326 rims?

Thanks for all the help from everyone.

[Maniac]

They're the pressures I'm using on my 19" 296's (2.4 front, 2.9 rear). I tend to run a little less 2.8 at the back and 2.3 on the front. Its just a touch comfier on crappy UK roads. I take them to 2.4 and 2.9 if I'm going on a long run/carrying passengers/luggage.

[jelmok]

Thanks for all the replies. I had another chat with the guys at Birds tuning in Iver and they asked me if I had worn tyres on the car - asked me to check the inside shoulder of the tyres. Mentioned that the run flats tend to wear unevenly, and that the inner shoulders often go first and combined with the stiff sidewalls on the run flats results in the tram lining I am experiencing. After checking again, it does look to me like the inner shoulders are more worn than the outers (which have loads of tread) Reckoned switching away from the run flats would transform the car. Not sure what I will do yet. Booked it in to have it checked at my local BMW dealer to make sure nothing is obviously broken and also check the wear on these tyres. Will decide what to do from there. To my mind if the tyres are wearing unevenly the tracking should probably be checked, but I am no mechanic by any means. Whatever the case - it's obvious from the replies from everyone that the is abnormal though, which gives me hope that this is curable! Will keep everyone posted! Thanks again.

[Maniac]

As I say, get the tracking done, its minimal cost and a simple pothole can whack things out of alignment. You might find that sorts it out as others on here are running run flats and don't have the same issue. Personally, having paid £680 for my last two rears, I'll be going non run flats next time as I've little double a) it will be cheaper and b) more comfortable and c) likely preserve my rather worrisome 296's!

[Gargybloke]

The tire wear can be ok but the tracking can still be out causing the problems you mention so dont discount it just because the tires look evenly worn.

Do you ski at all? I think Its a good analogy. If you go along with your skis dead straight, parallel, every small bump will push a ski off course. You have to concentrate real hard to not fall and stay in a straight line. If you point the tips a little inwards, at the front, you have more direction stability and are more comfortable.

Does sound like it could be the run "work of the devil" flats that could be the problem though.

[Breaker]

The only time mine got a bit twitchy was after I had 2 new rear tyres fited (18"). Seemed a bit vauge at speed going into corners! After a few hundred miles it all settled down again. Perfect now.

[a11y]

Do you ski at all? I think Its a good analogy. If you go along with your skis dead straight, parallel, every small bump will push a ski off course. You have to concentrate real hard to not fall and stay in a straight line. If you point the tips a little inwards, at the front, you have more direction stability and are more comfortable.

Great analogy - I've not heard it put like that before

I used to run toe-out (non-standard settings) on the front of a FWD hot-hatch: turn-in to corners was amazing but it did demand more effort/concentration on the motorway due to less direction stability (to use the terms above). That could be the issue with jelmok's Z4 - simple alignment issue. Like others have said, I'd start there as shouldn't cost more than £80 for a 4-wheel alignment. If not then I'm sure Birds will have a £££ solution - I've heard they can do wonders with the 1-series chassis setup so guess they could transform any Z4 equally.

[jelmok]

I'd start there as shouldn't cost more than £80 for a 4-wheel alignment. If not then I'm sure Birds will have a £££ solution

I'm hoping it's the former rather than the latter given I've just forked out for the car!! Curious about Breaker's comment about the two new rear tyres - I know mine had two new rear tyres as part of the AUC - so it could be something as simple as that!

[Z4andy]

I'd be more concerned about you not noticing the wheel firm up in sport settings.

Sounds to me there is a problem with the electric steering as you really do notice the wheel firm up once you select sport.

[jelmok]

Hey all,

Quick update and things aren't any better. Firstly a better description of the problem - basically when driving on a motorway at constant speed, car is great and tracks straight and true. However if you accelerate, it pulls right, and then when you come off the accelerator, it pulls left! Gets so bad that if you take your hands off the steering when it's running straight and accelerate, you end up in the right hand lane, then if you slow down, you pull into the left lane. Gets very unnerving especially as you are constantly trying to compensate.

Had the car at the dealer and had a KDS performed at their expense. Rear was slightly out, and they have fixed it, but it's no better. I even changed the car from run flats onto new Continentals and double checked pressures, but still not right.

At a loss now, dealer has raised a case with BMW technical, but are telling me it maybe torque steer and a possible characteristic of the car. This doesn't sound right at all to me. Any other thoughts? Could it be the power steering? Dealer reckons everything else seems normal?

Thanks for any help.

[moonshine]

im no expert, but the symptoms sound like torque steer, but that is usually a problem on FWD cars. Ive not heard of it on RWD cars. i don't know if it is possible to have torque steer on RWD?

[Maniac]

I'd have the dealer check the suspension again. That is either camber of the road or damage to a suspension bush imho

[jelmok]

I know - its not like I am really pressing on when it happens either. Just a small amount of acceleration or deceleration is enough???!!!

[MikeS]

Well what ever the dealer says it does not happen to my Z even at very high speed. In fact it is so steady that I hardly feel a need to hold the steering wheel.