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Hey all. I changed my '87 from 9.5x16" rims to 9.5x18". Started with Nitto INVO 255/40R18 tires, according to a tire calculator, this was supposed to end up the same dimensions, as in width and diameter.
Well, of course, wasn't sure how accurate my speedo was before the change, but after checking with GPS and the ol' milemarker run, found the speedo was 2 MPH slow at actual 79MPH. Not confident with the sidewall profile either, see pics:
Time for replacement (those INVO died quick and sucked, never again), re-thinking the tire size. Thoughts on switching to 265/35R18? Calculator says:
Using a tire comparison tool you're familiar with (I didn't recognize yours) maybe try a 275/35R18 - that should do well on a 9.5" wheel and maybe be very close or correct your speedo issue. Probably an identical error but you can tinker.
Are you trying to get the speedo closer than 2 MPH? I could believe there is that much difference between a new tire and one wore out but I did not do the math. I was always led to believe the car manufacturers wanted the speedo to read at least 2 MPH fast so they could not get sued for speeding tickets. Dan
A wore out tire should be 2 actual MPH slower, not faster. My speedo was showing 77 MPH when actually going 79. Might need to check my diff ratio, make sure a PO didn't pull a fast (slow?) one on me.
I'm also chasing the profile on the rim, not sure if the old were too narrow a look. Could use opinions.
Tire Size Opinions
