Go Kart Racing Gear Selection Using Gears and Tires



Posted: Sunday, September 10, 2006

by Carl McDaniel
Smokin Joe Racing

Most go kart racers know about gear ratio and racing go kart gear ratio charts are listed in numerous places. Racing go kart gear ratios are figured using the number of teeth on the rear sprocket of your go kart divided by the number of teeth on the clutch gear on your go kart engine. For example if you were running a 15t clutch gear and a 60t rear gear it would be 60 / 15=4. Simply put this means 1 revolution of the axle to 4 revolutions of the crank. But in order to get a true picture of a racing go kart gear ratio a karter must use rear tire circumference in the equation. If a kart racer is using the same gears as someone else but you have 34" rear tire circumference and someone else has 36", the true ratios are not equal. To figure the true ratio you will want to use IPR (inches per revolution) which simply means the number of inches a kart will travel per each revolution of engine.

To figure IPR use this equation: Rear Tire Circumference(T) x clutch gear(C) divided by rear gear(R) = IPR. For example if one racer(Racer A) was running a 15t clutch gear with a 60t rear gear and their tires were 34" the equation would be 34 x 15 / 60 = 8.5. This means the kart would travel 8.5 inches per revolution of engine. If another racer(Racer B) had the same gears but had 36" tires look what happens. 36 x 15 / 60 = 9.0.

Even though both these racers were using the same gears they were not running an equal set-up. Racer A would be faster coming off the corners and Racer B would be faster down the straight. So what if Racer B wanted to run the same IPR as Racer A but still use the same tires? To figure that we can replace Racer B's 60 with Racer A's IPR. 36 x 15 / 8.5 = 63.52. This means that for things to be equal, Racer B would need to change their rear gear to a 63t or 64t.

So remember, if you ask someone what gears they are using and you don't also ask what size their tires are, you are wasting your time. Think IPR, not gear ratio. Here's a link if you need a go kart racing clutch or rear sprockets, www.smokinjoeracing.com

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