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Today we're going to delve into the world of gearing and speed. This article is also going to be a bit more technical than previous articles so get out the calculator and lets have a go at it.

A typical pocketbike has a 6 tooth pinion (the gear attached to the clutch housing) and a 68 tooth sprocket (the gear on the rear wheel). This gives us the ratio 68:6 or 11.33:1.

By using simple math, you can take your gear ratio and find your top speed. This assumes you have a 10 inch tall tire and your bike is capable of 10,000 RPM

So the math shows us our bike can do 26.29MPH. This definately blows away and idiot who says his 49cc pocketbike can do 70MPH unless his motor is somehow running at 25,000 RPM!

So how do you go faster? Well in a previous article I mentioned users upgrading the parts of their bike and not going any faster. Why? Because you are limited by your gearing!

So lets say I want to go 40MPH with this bike. It is still pulling 10,000 RPM. We mix up the formula a little and we come up with this.

Now I just need to find a sprocket and pinion that can give me a 7.44:1 ratio. I decided to pick a 63 tooth sprocket and an 8 pin pinion which gives me an overall ratio of 7.875: 1 which is darn close to my goal.

Depending on what type of racing you are going to do, you will of course want to change your gearing to match. A shorter track you will want a higher gear ratio to give you better bottom end performance. For a long track you want a lower gear ratio to give you better top end.

Below are some gear ratios and their estimated speed using the above numbers.

Where you see a lower speed, using the above gearing, you will feel a better bottom end. This basically means you will get to your top speed faster, which gets you out of the hole and away from the riff raff so you can be in that wonderful #1 position.

Pinions range from 5 to 10 teeth (yes 9's and 10 DO exist), and sprockets range from 47 to 78 teeth. As you can see by the ranges avaialble there are hundreds of combinations that are possible. The more skilled and technical riders will have a number of pinions and sprockets with them and adjust their bike for each track.

So there you have it. A detailed explanation of what gearing can do for your speeds. I hope you all enjoy this article and have learned something from it.

This article was written by Bruce Peresky for pocketbikeforum.com. Copying is permitted provided you give credit to http://www.pocketbikeforum.com

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