Gear Ratio Guide

As a ballpark figure, for a 125bhp drag kart running standard kart rims and tyres, sprocket sizes should be in the region of

Front / 15 tooth - Rear / 22, 24, 26 tooth

Those combinations will give Gearbox to Rear Axle ratios of 1.46, 1.6, 1.7 to 1 (Rear รท by Front)

If you are installing a more powerful engine the kart will accelerate faster, will reach its top speed quicker and will be maxed out way before the end of the track

Therefore the gearing will need to be raised so smaller rear sprocket (ratio moves closer to 1)

If you are considering running larger tyres, they will cover more distance per revolution

The engine will be nowhere near maxed out at the top end so the gearing needs to be lowered so larger rear sprocket (ratio moves away from 1)

To calculate the percentage difference between different diameter tyres, measure the circumference of each wheel

Chalk a Line across the Tread - Roll it on the Ground - Measure the Chalk Lines

Divide the small tyre measurement by the large tyre measurement and multiply by 100

That will give the percentage difference between them

Divide original ratio by that percentage and that will provide the new ratio required

Calculate THE ratios for different front / rear combinations until the required ratio is matched

From the above it can be seen that gearing will not be the same for every kart

Tyre size and power output are the deciding factors so this information can only be used as a rough guide

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