What was the rear axle ratio of the Ford Model T?

What was the rear axle ratio of the Ford Model T? The standard ratio was 3.64:1.

That ratio means the driveshaft and pinion turned about 3.64 times for one revolution of the rear wheels. The standard differential used an 11-tooth pinion driving a 40-tooth ring, giving 40 ÷ 11 = 3.6363, normally rounded to 3.63:1 or 3.64:1.

The gearing reflected the Model T’s priorities: durability, usable pulling power, and acceptable performance on poor roads. Its two-speed planetary transmission was already unusual by later automotive standards, so the axle ratio worked with the transmission to determine acceleration, hill-climbing ability, and road speed.

Some Model Ts could receive optional “mountain” gearing of about 4:1, which improved low-speed pulling power at the expense of speed. That option is why 4:1 can appear in Model T specifications, but it was not the standard rear axle ratio asked for here.