The choice of tall, skinny, radial, 15" tires seems to be dwindling at a rapid pace, so I prefer the 4" wheel. Seems like you are stuck with the short VW style 165-175, or you have to jump all the way to 215/70 which is what are on my 4" centerlines and bulge quite a bit.

Just read, "Track only light weight race car", go 3 1/2, with as much out set as possible so they can clear whatever brakes you end up with.