It's not that tight. I don't know where you're getting your numbers for but it's definitely not 1/8. Not even close.
Ben, those numbers were from me getting under the truck to measure things out since my brother was wondering if there is enough clearance to use the D90 calipers with 15" rims. My quick & dirty measurement was 5/8" between the 16" rim and the closest part of the caliper, thus leaving 1/8" with a 15" rim.
I'll try to snap a pic and post it up later.