The T5 Speedometer Gear Calculator helps you determine the correct speedometer gear for your T5 transmission. This ensures your speedometer shows the accurate speed, avoiding potential issues with speeding tickets or misjudged driving speed. By inputting key variables like drive teeth, axle ratio, and tire revolutions per mile, you can calculate the exact gear needed for accurate speed readings.
Formula of T5 Speedometer Gear Calculator
The formula for calculating the correct speedometer gear for a T5 transmission (and most other transmissions) is:
Drive Teeth * Axle Ratio * Tire Revolutions per Mile = Driven Teeth / 1001
Here is what each variable means:
Drive Teeth: This is the number of teeth on the gear attached to the transmission output shaft. It is typically 7 or 8 teeth on a T5. You may need to consult your specific transmission manual or refer to a reference chart to find the exact number of teeth on your drive gear.
Axle Ratio: This is the gear ratio in your differential. It refers to the number of times the driveshaft rotates for every one revolution of the wheel. You can find your axle ratio on a sticker in the differential housing or consult your vehicle’s manual.
Tire Revolutions per Mile: This is the number of times a tire will rotate for every mile traveled. You can calculate this using the following formula:
Tire Revolutions per Mile = 63360 / Tire Diameter (inches)
63360 is a constant that converts inches to miles.
Tire Diameter (inches): This is the overall diameter of your tire, including the sidewall.
Driven Teeth: This is the number of teeth on the gear that connects to the speedometer cable. This is the gear you will be replacing to achieve an accurate speedometer reading.
Pre-Calculated Values Table
To make it easier, here is a table with pre-calculated values for common setups:
| Drive Teeth | Axle Ratio | Tire Diameter (inches) | Driven Teeth |
|---|---|---|---|
| 7 | 3.55 | 28 | 56 |
| 8 | 3.73 | 26 | 60 |
| 7 | 4.10 | 27 | 64 |
You can use this table to quickly find the correct driven teeth without calculating each time.
Example of T5 Speedometer Gear Calculator
Let’s walk through an example using the formula. Suppose you have the following values:
Drive Teeth: 7 Axle Ratio: 3.55 Tire Diameter: 28 inches
First, calculate the Tire Revolutions per Mile:
Tire Revolutions per Mile = 63360 / 28 = 2262.86
Next, apply the formula:
7 * 3.55 * 2262.86 = Driven Teeth / 1001
Driven Teeth = (7 * 3.55 * 2262.86) / 1001 = 56.38
Since you cannot have a fraction of a tooth, you would round to the nearest whole number, so the Driven Teeth would be 56.
Most Common FAQs
An accurate speedometer ensures you are driving at the correct speed, helping you avoid speeding tickets and maintain safe driving habits. It also ensures your vehicle’s odometer readings are correct, which is important for vehicle maintenance and resale value.
You can find your axle ratio on a sticker located in the differential housing or by consulting your vehicle’s manual. Some vehicles also have this information on a sticker inside the driver’s side door jamb.
While the calculator is designed for the T5 transmission, the formula can be adapted for other transmissions with similar gear setups. Always refer to your transmission’s manual for specific details.