Running slightly narrower tires on an M5?

[528i]

I have a set of rims that take 235s on the front and 265s on the back. What dangers or potential problems might I run into if I were to run these on an M5, which normally has 245/275s?

[RSPDiver]

On the existing wheels, probably little other than reduced (slightly) lateral traction capability. If you put the tires on the M5 stock wheels, the rims will be more exposed to danger. Can't imagine there would be any more or less tramlining though, if that's what you're concerned with. The overall profile is the same, right? As in, you aren't significantly changing the overal diameter of the wheel/tire combo, are you?

[528i]

On the existing wheels, probably little other than reduced (slightly) lateral traction capability. If you put the tires on the M5 stock wheels, the rims will be more exposed to danger. Can't imagine there would be any more or less tramlining though, if that's what you're concerned with. The overall profile is the same, right? As in, you aren't significantly changing the overal diameter of the wheel/tire combo, are you?

No, I'd be using the 18" Alpina rims with the 235/265 PS2 tires on them, instead of the OEM 18" (that are peeling finish off) with 245/275s tires. I would eventually replace them, but the set of HREs I want runs about $4000. Essentially all I am attempting to avoid is dishing out a bunch of money for new rims as soon as I get the car, since I know I would cringe every time I looked at that flaking paint on the OEM rims. I'm not trying to avoid tramlining or trying to save money when buying tires, just trying to make it look as pretty as possible until I can afford the HREs (and $1000 in new tires! Ouch :D)

So far it's just:
- speedo slightly off
- a bit less lateral traction

Anything else?

[Pinecone]

More understeer. You are dropping the front and rear one size, but that is a larger percentage of thesection width in the front than in the rear.