[KuKuRu]

Does anybody know what the «scrub radius» is in M4g82? How many millimeters is it?

Scrub radius is the very important parameter for the front chassis. It is always negative or zero. This is done on purpose so that the front wheels go straight with zero degrees. If you move the ET (Einpress Tiefe) than the scrub radius should change to positive degrees. Then the front wheels turn outwards, and the car may lose stability and the steering wheel will become sharp.

I want to change ET (ET20 > ET10/ET15) but this is not at the expense of driving.

[Hit_Apex]

It sounds like you are conflating scrub radius and toe. Spacers do change the scrub radius but the important parameter you describe is toe which spacers do not change.

[KuKuRu]

Originally Posted by Hit_Apex

It sounds like you are conflating scrub radius and toe. Spacers do change the scrub radius but the important parameter you describe is toe which spacers do not change.

These are different parameters. But they are related, of course. Camber / toe / scrab radius… +/-1 degree camber’s gives -/+3 millimeters of scrab radius. So you need to correct toe a bit… I need to understand what the scrab radius is with a standard camber (-1.5 degrees).

[Hit_Apex]

I understand the concepts. You may be overthinking this. If you just want to add spacers, you'll want to review the steering feel and handling behaviors this will induce (lighter steering feel and propensity to center, possible bump steer or brake steer depending on the amount of change). There is no right or wrong - your premise that it is always zero or negative is not a rule but agree is common in modern cars.

I don't know what the M4 SR is (if I had to guess it's zero or very close), but unless you're willing to add some aftermarket suspension parts to correct back to stock spec, spacers will move SR outward. I can tell you that 10MM will not cause a massive change in steering feel as a result of increasing SR. If you decide to do the measurements and test the differences, please share.

[KuKuRu]

It seems to me that only very brave drifters can put 10 mm spacers on the front. I have other interest – a raceway.

I don't want to implement spacers. I need wider sport-tires (cup2/ V105 / trofeo) for a dry raceway (I'll going to use stock 275/285 on the wet track).

Wide tires (295/305-315) don’t insert good into the arches. ET needs to be correct it. Outside for the front (ET15 or ET10), and inside for the rear (ET25 or ET 30). There are no problems with the rear, it goes straight. But with the front wheel, the issue depends on the scrub radius. The price of a mistake is a crash/ accident.