727/904 Speedometer Gears & Housings

A GENERALIZED rule (26-27 inch tire) can be had by taking the number of teeth in the gear and dividing by 10, or conversly multiplying your rear end ratio by 10 to get number of teeth on gear. eg 2.76 rear needs a 27 tooth gear, 3.91 rear needs a 39 tooth. This is junkyard math for a quick reference when you find one on the ground, but the formula gets you spot on when you have a choice. It works out to the rear*10 rule with a 26 tire pretty good.