You ask we answer. Here's the latest in our "Ask a Mechanic" series.
Q: How do I lower the gearing on my dirt bike?
A: Let's start off the new year with an easy one! An oft asked question which sounds like it has a complicated answer but lowering the gearing on your dirt bike, regardless of make, model and year is quite easy. OK, you do have to remove some parts so don't expect a quick five minute job.
To lower the gearing on your dirt bike you need to change the sprockets. Less sprocket "teeth" on the front sprocket or more "teeth" on the rear sprocket offers a lower gearing ratio which provides faster acceleration. If you ride a trail or mountain bike think of how you change the gears for climbing hills or maintaining speed - the same rule applies.
Therefore, one less tooth on the front sprocket (counter shaft) equates to adding three to four teeth on the rear sprocket in terms of lowering the gearing. To make a slight change in the gearing ratio, replace your current rear sprocket with one that has one or two more teeth and for a bigger change in gearing replace the front sprocket by one less tooth. For more top end, or faster top speed, do the reverse and remove teeth on the rear sprocket or add a tooth to the front sprocket. Keep in mind removing or adding teeth requires a change in the length of the chain.
Understand, replacing the front sprocket even by just one tooth contributes to a significant change in gearing, so I recommend making changes to the rear sprocket first before fiddling with the counter shaft.
You didn't ask why you should lower the gearing, so just in case, I'll offer some advice. A dirt bike with a lower gearing ratio works best for trail riding and technical Supercross tracks without a lot of straightaways. So, the more turns you plan to hit think about lowering the gearing.
However, most casual dirt bike riders don't bother with changing the gearing at all but feel free to experiment and see if that gives you different results.
