[71OLDS]

I can give you some feedback on my 71 Olds 442 conv. I'm sure we're not exact but I can provide some real numbers. Currently I run 305/45/18's on a 18x10 rim. BS = 5.5, diam = 28.8. Front = 255/45/18 on 18x8 rim. BS = 4.5, diam = 26.97.

Had Hotchkis springs on the front, no issues. Rear Hotchkis springs too but air bags allowed for height to be adjusted slightly. Had to roll wheel well lips and message inner fenders on one side. Pushing it on size w/305s in the rear (without mods) but got it to work. This was with stock front suspension and brakes.

Now considering uping to 20s. A few new issues. Added coil overs and B-body spindles w/Baer 13" rotors to the front. This pushed the front wheels out about 1/4" to 1/2" If I get new rims may go w/245 or 255/35/20 w/18x8 rim and probably 4.75 BS....or maybe even 5 BS..need to push rim inwards. Height around 26.5" to 27" should be OK, taller could be a problem.

For the rear adding the 12" Baer rotors caused issues too. The thicker rotor (from stock drums) required 1/2" longer studs and pushed rear rims out about 1/4" to 1/2". Considering 20x10 w/ a 305/35/20 (28.58" on Nitto drag radials) and probably a 5.75 or even 6 BS. Car is not "rolling" yet. Once it is can get exact measurements but this may help w/your #s. I think your suspension and/or brake selection should be accounted for when choosing BS and height.

-Joe