I have an '85 GS and I recently put a limited slip from the GSL-SE in it. I'm not sure how to recalibrate the speedometer and odometer, if they need it at all. If anyone has any suggestions I would appreciate the info.

 

It's change by changing the speedometer gears.

Stock is a 5-tooth gear on the transmission and a 17-tooth gear on the speedometer cable. Going from 3.91 to 4.08 gears means your speedometer gear needs to be 1.04 times as large as the one you have now. A 18-tooth gear will be just a little too large (math works out to 17.7).

My advice is to drive it on a marked road and compare the odometer readings to the mile marker readings. Ignore the speedometer since it probably reads too high anyway. (Most people report their speedos reading 10% or more too high even with stock tires/gearing) If your odometer is more than 1 tenth too high over about 3 miles then you should probably hunt down a 18-tooth speedometer cable gear. Or just go for the -SE sized tires - Mazda used the same speedometer gears on the -SE as the 12A cars, the taller tires on the -SE canceled out the lower gears.


edit: bodged the math, but it's fixed now

 

Thanks, I'll be taking a little trip tomorrow so I can check the odometer. I'm probably going to get different rims and tires eventually but for now I would like to be as close as possible.