Tech Center: The Weird and Wonderful World of Gear Ratios

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Gearing
Sport ATV riders and racers alike often spend big bucks on performance enhancements but overlook a simple means of changing the delivery characteristics of their machine’s engine output: the final gearing.

We often talk of gearing a quad up or down and it sounds complex on the surface when in fact it’s a simple matter of the ratio created by the two external sprockets on the ATV (linked together by the drive chain).

The Basics

The two sprockets in question are the countershaft sprocket – which attaches directly to the engine and is typically located just behind the rider’s left-side boot and the rear sprocket, which attaches to the rear axle/ drive wheels.

Contrary to common misconception, when your ATV leaves the factory, it is likely not set up with a ratio specific to the type of terrain and riding style you prefer. How do we know? Because engineers who design new quads can only guess what you are going to do with your machine. One person may be screaming over massive triples while another may be poking along through a muddy field on the same identical hardware.

More often than not, manufacturers select a gear ratio designed to be as user friendly for the greatest number of users right out of the box as possible and while it is nice that they don’t want to intimidate a novice rider or make a fool out of him by stalling out on his test ride, the best way to select a ratio that works best for you is to slap on fresh sprockets.

Up & Down

Gearing a quad up or down sounds more complex than it really is. Up refers to a taller gear ratio, which translates to more overall speed throughout the powerband. Gearing a machine down means a lower ratio and hence harder acceleration at the cost of top-end speed throughout each gear.

So how does one go about gearing up or down? Simply this:

Less teeth on the rear sprocket or more on the countershaft = gearing up.
More teeth on the rear sprocket or less teeth on the countershaft = gearing down.

In Action

Generally riders make changes to the number of teeth on the rear sprocket rather than on the front or both sprockets simultaneously simply on account of the ease of access when compared to reaching and removing the countershaft sprocket. Additionally, it’s rarely a good idea to fiddle with both sprocket teeth combinations simultaneously as the results are generally amplified and it can become difficult to tell which is responsible for what.

Ratios

Calculating the gear ratio is surprisingly simple and makes for having to worry about a few less numbers in your head. Take the bigger number (the rear sprocket teeth) and divide it by the smaller number (the countershaft sprocket teeth)- that gives you your gear ratio.

This makes sense too because it’s in essence telling you how many times the smaller sprocket has to rotate to equal one rotation of the bigger one (and hence the rear axle and of course with that the rear wheels themselves).

The Final Verdict

Keeping in mind your ATV’s gear ratio is a relatively affordable and simple means of making noticeable changes in performance. Spending big bucks on engine modifications or exhaust systems is often money squandered if the machine isn’t delivering its power in a means effective for your riding style or conditions.

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