Speedo Fix

[Stange86]

Just upgraded my wheels to 20 inch shelbys and I need to know the revoulutions per mile to recalculate it. Does anyone know?

 

[bdcardinal]

http://www.miata.net/garage/tirecalc.html

Literally the best tool out there. It is what I use at work when people want to change sizes.

 

[TT5.0ca]

Doing it legit in your garage, since this is not as simple as plugging numbers in, as diameter changes all the time.

Dab of grease on centre tread, roll car til the grease hits twice, measure the distance between centre of the spots in inches. Convert a mile into inches, (63, 360)

Divide 63360/your distance measure = RPM of your actual tire, as close as you'll get it.

 

[Stange86]

Cardinal I tried that but it's not matching up. The site says it should be 740 but my car stock has it at 756 revs per mile

 

[TT5.0ca]

Just do it my way. It works and is as accurate as it can possibly be. The online calculators are at best a SWAG.