Speedometer Gears from Speedometer World. We sell speedometer gears, odometer gears, speedometer cables, speedometer housings and ratio adapters. Worlds Largest Selection of Rear Wheel Drive American Speedometer Gears. #1 in Sales World Wide. Buying Speedometer Gears Just Got Easier. We Ship Worldwide. Variables such as the vehicle’s axle ratio and tire diameter affect the accuracy of the speedometer.
To determine your tires true diameter in relation to determining what speedometer gears you need, measure from the ground up to the center of the axle then multiply by two. The actual run out of the tire can be as much as 2 to 3 inches less than what the circumference of the tire measures. In effect your tire has two diameters.
To determine your rear end ratio, raise both tires off of the ground, turn both tires at the same time one complete turn, at the same time count the turns of the drive shaft, this is your ratio.