How much clearance for wheel runout / sidewall deflection

[Derek357i]

I want to keep my tires as "tucked in" as possible, but at the same time I don't want any rubbing of the sidewall on the inner wheel well. How much clearance is needed between the tire and any part of the chassis or fender to allow for wheel runout or sidewall deflection.

I am going to swing the trailing arm through its entire range of motion and use an aluminum shim at the rubbing points of the required thickness to ensure I have the clearance I am seeking. The sidewalls are short and stiff as hell, so I can't think I am going to get much deflection there.

I am initially concerned about the rears. I am running 285 30 18 on a 18X10 rim. Fronts are 255 35 18 on 8.5. Yes, I know I am going to have to run flares :D

[riverdale21]

I would wager that at minimum a 10mm space should be there when the wheel is at its closest to the fender during its range of motion. If you are using a tire with a less stiff sidewall you should shoot for more like 15mm. Err on the side of safety.

[E30-323ti]

The tyre will only deflect where it contacts the road, If you have solid or urethane bushes non of the suspension should deflect either thus: don't worry about it!!

285's sound a bit OTT. an E30 is only a light car and you'd be lucky to get enought heat into those tire to get any traction, unless you plan to keep it wheel spinning the whole time (which shouldn't be hard!!).
I'm hoping to go with 235/40 17's all round.

Have you got any updated pics etc... yet Derek???