Palmo

Hi Folks,
Some of you may remember my previous threads about ongoing instability in cross winds with my car. The car has done this from new and I have never been able to get to the bottom of it.
Also, I am now getting uneven tyre wear, this is now across all 4 tyres. The car has done 33k miles - front tyres are original, whilst backs were replaced after around 18-19k miles (can't remember exactly when now).

Anyway, following lots of discussion with BMW UK, I had a KDS Geometry Alignment done today at a local dealership to see if this was the culprit i.e. out of alignment causing both instability and uneven tyre wear?

The results are as follows:

Front tyres have covered = 33k miles (always run with 2.1 bar of pressure).
Rear tyres have covered = 14-15k miles (always run with 2.5 bar of pressure).

Tyre Depths

Inner / Middle / Outer (all in mm)

Right Hand Front: 3 / 4 / 2
Left Hand Front: 2 / 5 / 3
Left Hand Rear: 2 / 3 / 4
Right Hand Rear: 3 / 3 / 4

Alignment Results

Attached below are the actual alignment figures ? including before & after. Sorry but my scanner is not currently working so I have taken a picture - not sure if people will be able to read this?



According to the Service Manager, everything was in spec (hence green) apart from the Right Rear Toe (see red). He commented that he didn't think this would be enough to be causing the stability issue. What do any of you guys think? Could this be the cause?
Not sure what the SAI refers to as these figures are also in red? I questioned if this meant they were out of spec but was told no!

Drove car home and it feels fine - but this is the problem, it is only unstable if there is a breeze - moderate (or above) wind. Today there isn't so I can't tell if this is cured or not. The car does drive fine though (with no wind present today)! I'm also aware that I will need to look at replacing the tyres in the near future.

What do you folks think?

Rob Hall

Have you done or is it possible to try another e60 of very similar spec to see if that has the same probs. It does seem from this thread that stability is a general issue for some and not others. http://forums.e60.net/index.php?showtopic=47995
Dont know if theres any connection with yours but with mine on the motorway you really had to concentrate in a cross wind with the sport dampers, but when i changed to the konis, the problem has reduced enough to say it isnt a problem

Rob Hall

Have you done or is it possible to try another e60 of very similar spec to see if that has the same probs. It does seem from this thread that stability is a general issue for some and not others. http://forums.e60.net/index.php?showtopic=47995
Dont know if theres any connection with yours but with mine on the motorway you really had to concentrate in a cross wind with the sport dampers, but when i changed to the konis, the problem has reduced enough to say it isnt a problem

Palmo

Trying another e60 of similar spec maybe the way to go. But.....the problem is, that mine feels excellent 90% of the time. In normal 'calm' conditions it feels completely stable - I have 100% confidence in it at any speed. Add a little wind into the mix and it's a whole new ball game! Difficulty is getting to drive 'another car' on a day when these particular conditions are present.

Maybe the geometry adjustment has now helped - time will tell.

Also I have done a little reading and found that the SAI is the 'Steering Axis Inclination'. This is "the measurement in degrees of the steering pivot line when viewed from the front of the vehicle. This angle, when added to the camber to form the included angle causes the vehicle to lift slightly when you turn the wheel away from a straight ahead position. This action uses the weight of the vehicle to cause the steering wheel to return to the center when you let go of it after making a turn. Because of this, if the SAI is different from side to side, it will cause a pull at very slow speeds. Most alignment machines have a way to measure SAI; however it is not separately adjustable. The most likely cause for SAI being out is bent parts which must be replaced to correct the condition. SAI is also referred to as KPI (King Pin Inclination) on trucks and old cars with king pins instead of ball joints".

Looking at my results shows the SAI to be out of spec, although both sides are virtually even? Interesting to note from the above quote that this measurement is usually 'not separately adjustable'? Wonder why mine is out here and if this is causing any problems?

Any alignment experts out there care to comment? Also, does anyone have a print out following a KDS on an 'M-Sport' car that they could post up to compare with mine? Would be interested in the SAI values in particular.

Palmo

Anybody?

Rob Hall

i would say that if the sai / castor angle is the same both sides but out slightly that wont have an effect on stability, if it were different each side then it could. Worth noting that the strut top mnt holes are slotted slightly so there is a small amount of individual adjustment.
Always worth checking the rear suspension for wear or excessive play/soft bushes as thats where problems are usually found with straight line instability if the supension and geometry is basically sound.
Also did the alignment check include a corner weight check ? inaccurate corner weights could cause instability probs too.

Palmo

Thanks for your comments. The car was checked over and I don't believe there are any issues with worn suspension components, besides, the car has done this from brand new - it has now covered 33k miles. Not sure if the alignment included a corner weight check? All I know is that is was a KDS alignment through a BMW local dealership? Is this normally included?

Rob Hall

I dont know if a kds alignment includes corner weight checking, but im guessing not if you dont know about it, would be very interesting to see the results if they were checked. If the dealer cant do it, would require a more specialised shop perhaps more motorsport orientated.
I cannot understand why more alignment shops dont have corner wht checking facilities considering the importance of it, maybe because unless youve got coilovers its difficult to do anything about it if there not accurate.

Palmo

I've done a lot of reading on the net about geometry set-up, and the more I read, the more I'm inclined to think my problems are related to the Caster & SAI.

Rob Hall

what are the sai and castor figures Palmo, i cant make them out on your sheet ?