Re: adjusting the speedo to fit the new tires.
You are off by a percentage and it can be fixed for a few bucks. A replacement gear can be bought at your local Jeep dealer or from many of the parts houses including Parts Mike. Costs about $8 to $11 for the gear and a few minutes to install.
The gear is located in the rear tailshaft housing on the backside of your t/c where the speedo cable attaches.
To determine what gear you need, use the following formula: Drive the vehicle to a highway with mile markers. Record odometer reading at a mile marker, drive ten or more miles, then record odometer reading again. Calculate miles traveled according to the odometer, including tenths of mile.
Use the following formula to find the number of teeth needed on your speedometer driven gear.
B = Miles traveled according to odometer
A = Actual miles traveled (per mile markers)
T = Number of teeth on driven gear used to calculate miles traveled
(B/A) * T = Number of teeth needed on driven gear (round off to nearest whole number)
Example: B = 16.4, A = 17, T = 41 (16.4/17) * 41 = 39.55 rounded to 40
When rounding decimals off: .50 or less round down, .51 or more round up.
If you get your speedo withing 2 or 3 mph of accuracy you are doing pretty good.
Good luck! Ken.
83 CJ8, 4.0 HO/AW4, 2.5 Superlift, 1" Daystar body, 33x12.50 GY MTs, 4.10, Lockers f&r, ob air, Custom bumpers, rockers, and skid plate, etc.