Here is another speedometer calculator program which you can download and run on your computer. Along with the metric tire size format (ex. P275/65 R15), this program also allows you to enter the tire diameter in inches, or enter tire circumference in inches. This is helpful when you can take simple tire measurements with a tape, or where the tire size markings are given in inches.

A useful option is given for rounding the calculated gear tooth count. This is helpful in a situation where the exact tooth count may not be available. For example: if the calculator says you need a 17 tooth driven gear, but you only have a 16 tooth or an 18 tooth gear available to use, deselect the “Round answer” option. In this example, if the unrounded answer comes out to 16.62, then a 16 tooth gear would be closest to what you need.

Download instructions: Click on the download link below to download the zipped file. Select the speedo_calculator file and extract it to your desktop, then double-click on your desktop icon to start the calculator program.

SPEEDOMETER GEAR CALCULATOR

When a customer changes the tire size or axle ratio on their car, the speedometer no longer reads correctly. A shop must then change the speedometer gears to try to compensate and bring the speedometer back to calibration. About 99.9% of the time this is done by trial and error.The shop changes the gears and then drives the car. They keep changing gears until they guess that it is reading fairly close. This takes many hours and often ends in error.

With ATRA Online, this problem can be solved in a few seconds.You will need to know the number of teeth on one of the speedometer gears, the tire size and the axle ratio. The system will then compute a new tooth count for the other speedometer gear.