IMPERIAL
The rolling radius of loaded driving tyre is 168 times the overall gear reduction times the miles per hour divided by the engine speed.
![1](https://de.webtec.com/api/i.aspx?wteqi12a.gif;98;29)
Where:
168 = Factor
RPM = Revolutions per minute of the motor
r = Rolling radius of loaded driving tyres in
inches
R = Overall gear reduction including both axle and transmission
Example:
Find the rolling radius of loaded driving tyre of a vehicle where the overall gear reduction is 10, the miles per hour 15 and the engine speed 1680 RPM.
![2](https://de.webtec.com/api/i.aspx?wteqi12b.gif;143;29)
METRIC
The rolling radius of loaded driving tyre is 2651.51 times the overall gear reduction times the kilometres per hour divided by the engine speed.
![3](https://de.webtec.com/api/i.aspx?wteqm12a.gif;117;29)
Where:
2651.51 = Factor
RPM = Revolutions per minute of the motor
r = Rolling radius of loaded driving tyres in millimetres
R = Overall gear reduction including both axle and transmission
Example:
Find the rolling radius of loaded driving tyre of a vehicle where the overall gear reduction is 10, the kilometres per hour 20 and the engine speed 1500 RPM.
![4](https://de.webtec.com/api/i.aspx?wteqm12b.gif;143;29)