Speedometer Gear Adjustment for big tires on a GenI Montero/Raider
Many of us who enjoy our GenI Montero/Raider offroad have switched to a larger tire size other than stock. A problem with this that you may or may not have noticed is that the larger diameter tire sizes throw the speedometer off. The disparity between actual traveled speed and displayed speed grows in proportion to the larger diameter of the tire.
I first noticed this a few years ago when an officer issued me a ticket for a speed that was 3mph over what I thought I was doing. Even though I knew I was speeding, the speed written on the ticket bothered me as being inaccurate. Fast forward 2.5yrs later to my next speeding ticket and I was in disbelief at the speed the officer said he had clocked me doing. This caused me to take action and look for a possible solution that has plagued most of us larger tire users for some time.
Actually, I made the discovery quite by accident as I was looking for reasons my speedometer needle was bouncing (different tech story). I pulled off the speedometer drive gear assembly to learn how it works. It’s really pretty simple: a nylon gear is turned by a screw on the output shaft.