Axle Ratios and Performance

Kirk Wright apparently built a Model T engine that produced around 200 hp. Knowing this I asked him if there was a simple way to improve the performance of my Model T pickup.  He suggested that I change from standard 3.63:1 to 4:1 gears.

There is a feeling among many T owners that moving to 4:1 gears will reduce reduce top end performance.  This is true if you are driving a light car but at the same rpm the difference isn't that much.

Let's say your top touring speed is 50 mph.  Most of us don't tour at that speed.  Tim of course sometime slows down to 50.  With stock gears 2,000 engine rpm push the car along at 50 mph. With 4:1 gears, 2,000 rpm yields 46 mph. At 1,600 rpm, max horsepower for a T and a great touring rpm, 4:1 gears slow you down from 40 mph to 37 mph and in hill country you will be smiling.

If you are comfortable using a spreadsheet program on your computer click on the link below.  It will save a file to your downloads folder.  Double click on the file and if you have spreadsheet software on your computer it should open. There are three variables you can play with: tire diameter, differential ratio and engine rpm.

Robb Wolff

Gear Ratio Speed Calculator