off centre top mounts

Road suspension is a compromise.  Don't confuse this with 'optimised'.  BMW's opinion on what people want isn't going to be right 100% of the time for everybody.  Some prefer stiffer, some softer.  The factory settings are what they feel the majority of us might want.

 

We should be aware that this doesn't mean it’s THE answer to a road set up.  If you're not happy with how it feels then I guess you should try something different.  If you don't like the added tyre wear you can add the mounts and decrease negative camber.

 

What is it that you're after Danny?  Please don't say a definitive road suspension set up. There isn't one, its too subjective.  Reading over this thread it seems tyre wear is your (or was your) main concern.  That's an easy one to fix.

I hope I'm not coming off too cold.  Just trying to get to the point and help if I can.

 

Take care,

Jake

 

Uwe, when you do a trackside adjustment of the top mount what do you do about the front toe setting?

As the strut top forms one end of the kingpin axis the steering arm is essentially attached to it. When you move the top mount inboard you're going to increase the toe-in on the front wheels a fair bit at the same time as the track rod length stays the same but the kingpin moves inboard.

I assume most race teams would have track side geometry kit to bring the toe back to a sensible setting again.

Pooky wrote: Uwe, when you do a trackside adjustment of the top mount what do you do about the front toe setting?

To be honest, I just don't care!

Pooky wrote: As the strut top forms one end of the kingpin axis the steering arm is essentially attached to it. When you move the top mount inboard you're going to increase the toe-in on the front wheels a fair bit at the same time as the track rod length stays the same but the kingpin moves inboard.

Phew! My head is smoking after reading that.
Because it's very difficult to understand all the Kingpin stuff I took the car on a Supertracker and moved the mounts because I wanted to know what's happening.
Guess what? Toe changed so minimal that it was hardly to see on the scale

Pooky wrote: I assume most race teams would have track side geometry kit to bring the toe back to a sensible setting again.

Correct! But I am not a race team, and neither do I want to waste a lot of track time about 0.5 degrees (or even less!) which will not do any harm to my average driving skills.
I have been in Motorbike racing for 10 years and was running after every tenth behind the comma because I thought this is essential, but surprisingly I have had a few good races with my picked up after a crash bike with the settings all over the place

Don't get me wrong, I prefer the setup to be as good as it needs to be. But most off all I want to have fun on the track and not get stressed out by Kingpin and Ackermann (or whatever that bloke's name is )

UweM3 wrote: Phew! My head is smoking after reading that. Because it's very difficult to understand all the Kingpin stuff I took the car on a Supertracker and moved the mounts because I wanted to know what's happening. Guess what? Toe changed so minimal that it was hardly to see on the scale

Interesting, just wondered how small you mean. The toe tolerance is going to be between +/- 0.16deg from nominal setting, the car is quite sensitive to it.

We have just done some tyre wear investigations at work and come up with a max total toe-in setting of 0.5 deg (0.25 deg per side), there or there abouts depending on camber (any more and the steering feel goes a bit wonky anyway). The standard BMW setting already has a fair amount of toe-in to start with but I guess tyre wear just from one day is not really something to worry about.

The investigations did show that as you increase negative camber increasing toe-in at the same time does help with tyre wear, may be of use to people running lowered cars.

Edited by Pooky

Pooky wrote: Uwe, when you do a trackside adjustment of the top mount what do you do about the front toe setting? As the strut top forms one end of the kingpin axis the steering arm is essentially attached to it. When you move the top mount inboard you're going to increase the toe-in on the front wheels a fair bit at the same time as the track rod length stays the same but the kingpin moves inboard. I assume most race teams would have track side geometry kit to bring the toe back to a sensible setting again.

I can't quite remember but doesn't the steering arm mount to pretty much the bottom of the strut? So it doesn't really move when the top of the strut it moved inboard.

Some of the e30 guys in Germany seem to running
with 1995 spec e36 M3 control arms, this pushes
the wheel forward in the wheel well to give extra
caster/ camber also another effect of this will be a
increase in the ackerman effect on the inside wheel
when cornering due the the geometry of the steering
arm changing. This will help to 'pull' you into the
corner when you first turn in.

Yes Uwe, but putting a bit of caster would even be more simple than putting more camber...basically its the same mod you have to do: 3 holes.
You would have better effects than with camber PLUS you would not have to change anything when arriving at the track, since this is also of great mod for road use...

Yep Uwe what CoolCat is saying is that you could have all that, but instead of move the top of the strut inwards move it rearwards.

Giving an increase in caster rather than camber. So when the wheel turns you get move camber but straight ahead you get factory camber and no wear problems.

It's quite easy to visualise, with the strut leant back when the wheel moves round it the outside tyre gets more negative camber.

That's the theory anyway.

Can't agree with you Pooky, in the way that you present it al least.

In the real world the overall change you experience on your front end, changing from 6 to 8' caster is anything but miniscule, you almost have the feeling you have changed for another car!
And as you know, a bigger caster does so that the more you turn the wheels, the more camber variation you get, proportionaly.
That means yes, if your average corner is 1/8th of a turn of the steering wheel, you are right change will be almost non existent. But being in a corner at grip limit with 1/8th of a turn means your speed is somewhere around 250/270 km/h. A speed that requires almost no camber.
On the contrary, if you are in a tight bend at grip limit at 70 km/h, then you will certainly have almost one full turn of the wheel, and the variation in camber produced by the 6 to 8 caster mod will do for more than 0,5' aditional camber. And precisely this is when you need camber.
This is also another advantage of caster, it is sort of adaptative according to bends/speed...

Thanks Mike for putting it in simple words

Oh, one more thing about caster: on the M3, especially on the E36/E46, it is better to add it changing the rear mount of the wishbone than moving the top mount of the strut. On the E30 it is less important, or you can do both...

CoolCat wrote: Can't agree with you Pooky, in the way that you present it al least. In the real world the overall change you experience on your front end, changing from 6 to 8' caster is anything but miniscule, you almost have the feeling you have changed for another car! And as you know, a bigger caster does so that the more you turn the wheels, the more camber variation you get, proportionaly. That means yes, if your average corner is 1/8th of a turn of the steering wheel, you are right change will be almost non existent. But being in a corner at grip limit with 1/8th of a turn means your speed is somewhere around 250/270 km/h. A speed that requires almost no camber. On the contrary, if you are in a tight bend at grip limit at 70 km/h, then you will certainly have almost one full turn of the wheel, and the variation in camber produced by the 6 to 8 caster mod will do for more than 0,5' aditional camber. And precisely this is when you need camber. This is also another advantage of caster, it is sort of adaptative according to bends/speed... Thanks Mike for putting it in simple words Oh, one more thing about caster: on the M3, especially on the E36/E46, it is better to add it changing the rear mount of the wishbone than moving the top mount of the strut. On the E30 it is less important, or you can do both...

I've only being vehicle dynamics as a job for 10 years, so thank you for correcting me.