275 tire fit?

[justforfun]

67 firebird.
59.75" -rear outside drum to outside drum (BOP 8.2)
275/50/15 on 15x8 with 5" BS

6" -wheel mounting surface (outside drum) to inner wheel well
6" -BS + extra sidewall width

this should rub right? About 2 years ago with the car on the ground (stripped now) i cold almost fit my hand between the inner wheel well & sidewall. While driving it rubbed the inner wheel well (rub marks are still there).

does the tire change maxium width when supporting the car weight or are my measurements just wrong?



- i am looking at 275/35/18's on a 10" rim, but by the above measurements there is no way the typical suggested 5.5-5.75 BS will clear the inner fender well.