Difference between front wheel well liners M and non M

[Panta Rhei]

Has anyone come to a conclusion why those parts have different numbers?
I am certain for sure that it cannot be because of a cover behind a fog light (M air duct in this place), because I have seen M bumper conversions and non M wheel wells front are p&p when you replace cover with air duct and also lower part which attaches to the M bumper itself.
Rear one left side is the same for all E85/E86 but right is unique only to M models, I guess because of dual exhaust and no battery box

EDIT: https://z4-forum.com/forum/viewtopic.php?t=120295
Still, 225/45 is bigger in diameter by 22,5 mm than 225/40 meaning + approx 1,1 cm of higher tyre, how can you fit that in there if I cannot put my finger between tyre and wheel well front part (pic below). I have like 0,5 cm of space so how can Z4M accomodate 225/45 tyre turn wheels and do not rub?

Can you elaborate more?

There was also an idea in my mind that maybe it's been "streched" in horizontal dimension (front-rear) so that it can accomodate 225/45/18 instead of 225/40/18.
Pics for reference.

 

[GuidoK]

Could indeed be a clearing issue. Not only ride height and wheel offset is different to the z4m, but it also runs more caster, so the side of the tyres go up when steering.
On the non M z4 tyres start to rub pretty fast when lowered and steering in sharp corners (hairpins), with more caster this only gets worse.

 

[Panta Rhei]

Yes I am aware of a different suspension and whell's offset, but that is only left-right margin which in my opinion does not have any influence on front rear free space in wheel arch.
Even if i push my oe wheels towards engine for like 10 mm even 20 mm I would still not put my whole finger between tyre and wheel arch when wheels are turned.
Moving wheel in left or right direction (as pictured) has nothing to do with it since we have a conflict in the center of wheel well liner (marked green).

 

[GuidoK]

Yes I am aware of a different suspension and whell's offset, but that is only left-right margin which in my opinion does not have any influence on front rear free space in wheel arch.

Caster on the z4m is achieved by non symetrical (offset) rear bushings.
They push the front wheel forewards to achieve more caster afaik.

 

[Panta Rhei]

That is very interesting and maybe there is more to it than a simple play between offsets and ride height.
And I started this discussion because I want to fill wheel arches better with 225/45/18 255/40/18 on standard E85. Rears are no issue, but how can one guy have rubbing issues and the other one says it is fine even on 5 mm spacer up front on OE 8x18 ET 47 wheel. So many mysteries.

 

[GuidoK]

Btw your picture shows the wheel turning out.
But it's the wheel turning in that hits the liner.
This is because the suspension geometry (well, virtually every suspension geometry) has a scrub radius (purpose of this is also to lighten the steering; no scrub radius makes it very heavy to turn the wheel).
This also pushes the wheel foreward when steering in (and moves the wheel backwards when steering out).
The scrub radius is also effected with the rim's ET value (provided the same hubflange), and that is also different on the z4m (a bit of the same like installing spacers, they also increase the scrub radius)

If you want to know a lot about suspension geometry and how it works with all it's formula's, 'the automotive chassis' by Reimpell/Stoll is a good read (and a pretty heavy read).
It's out there in PDF :wink:

 

[Panta Rhei]

I would rather just buy a set of worn 225/45 for cheap $ and try it myself
But here is what I forgot. When you lower the car, the dimension becomes smaller for wheel to turn freely. You are lowering the car and arch comes down taking back this space. Blue dimension gets smaller as green dimension goes smaller - arch goes down.