Hi Everyone I just put a 6 inch lift on my 06 Ram and I put procomp 325/65/r18 on. Does anyone know the revolution per mile. my speedometer is off by 4 miles per hour. Thanks

 

Your speedo is electronic which is fed a signal by the computer. How may inches tall are the tires and what gear ratio is in the rear.

 

1- Mutiply the tire diameter ininchesby 3.1415926 then divide by 12 will give you feet perone revolution.
2- Divide 5280 by the answer from line 1 and it will giveyou the revolutions per mile.
3- Multply answer from line 2 by the speed in mph you want to know theRPMof the tire and then divde by 60 and you will have the rpm at that
speed.

sorry if this sounds like an IRS tax form but it will work.