THE CONVENIENT CYCLIST

How to always choose the right gear

Depending upon the model of CHANGE bike you choose, you’ll have anywhere from 24 to 30 gears (well… 22 gears on the 602 mountain bike, but we don’t usually keep that in stock).

That’s a lot of gears to choose from, and not all gear choices are the same. It doesn’t have to be complex, but it does require some basic understanding of mechanical advantage.

Basic mechanical advantage 1: increasing force

Everyone knows what a wrench is. Lots of motion with your hand, and the nut turns a little. With a long enough handle (i.e., enough mechanical advantage), you can apply enough force to conquer even the most stubborn nut.

It’s the same with gears. Spin a small gear a lot to turn a large gear slowly with force. This is how you can lift a car slowly with a hand pump jack or spin your pedals fast to conquer the steepest hill.

Small gear turning big gear = more force. (Ignore the 3A. photo credit technologystudent.com)

Basic mechanical advantage 2: increasing speed

Everyone who has a dog knows what this marvelous invention is. Flick your wrist a little to make the ball sail through the air.

It’s the same with gears. Turn large gear a little to spin a small gear with speed. This is how you can pedal slowly down a large hill while your wheels go really fast.

Big gear turning small gear = more speed. (Ignore the 1A. photo credit technologystudent.com)

On a bike, both gears turn the same direction because they are connected by a chain. But the basic physics above still applies. Note the terms cassette for the back and chain wheel for the front.

 

Basic bike gearing 1: your middle chain wheel gear.

A CHANGE 609 mountain bike has this gearing:

  • Chain wheel : 22-34-44 teeth in the front
  • Cassette: 11-13-15-17-20-23-26-30-34 teeth in the back

 

The SRAM 9-speed cassette exemplifies that rare, sublime convergence of quality and affordability.

Let’s start with the middle gear of the chain wheel. If you combine it with the largest cassette, you get 34/34 or one wheel revolution for every pedal revolution–great for climbing hills. Or combine it with the smallest cassette, to get 34/11 = 3.09, or three wheel revolutions for every pedal revolution. If a range of 1:1 for uphills and 3:1 for downhills and level ground is enough, you may spend all your time there, just adjusting the rear derailleur as needed for rolling hills.

Basic bike gearing 2: extending your range.

But sometimes, you may have a super-steep hill and no energy, or a big downhill and the “need for speed”. If your gearing takes you lower than 1:1 or higher than 3:1, then it’s worth it to switch to another chain wheel gear–otherwise, not so much.

Climbing a steep hill, you can go down to 22 (small gear) on the front and 34 (biggest gear) on the back, for a ratio of 22/34 or 0.65. The next five cassette gears are also below a ratio of 1:1 when combined with the small chain ring gear, so they help on hills.

Descending a hill, or with energy on the flats, you can combine a 44-tooth front gear with the smallest three cassette gears, for a ratio up to 4:1. Beyond the third cassette, you’re under 3:1 and redundant with the middle chain gear.

What to avoid.

Ultimately, you want to be in the “right” gear for your needs with as little stress as possible on your body or the bike.  Your bike is built for  mid-range gearing or extending down (small to large) or up (large to small) for hills. These combinations keep your chain relatively parallel to an efficient center line, regardless of gear selection.

What you want to avoid is cross-overs, such as large-to-large or small-to-small, both of which cross the center line to apply angled forces to your gears with no added value.

No added value? Let’s do the math. Small-to-small is 22/11 or a ratio of 2:1, which you can achieve just fine with the middle chain gear and no angled forces. Similarly, large-to-large is 44/34 or a ratio of 1.29, which is also within the middle chain ring range–without angling your chain or putting lots of stress on a really tight chain.

Summary: Four simple rules.

The gearing we’ve reviewed is for the CHANGE 609 mountain bike, and details for other bikes differ slightly. But these four general rules apply anywhere:

  1. Climbing power = small gear to large gear
  2. Descending speed = large gear to small gear
  3. Avoid full cross-overs of large-large or small-small.
  4. Middle chain gear is usually the one you will likely spend most of your time in

That’s it. Now you’ll never be that sweaty person standing up on the pedals struggling to push a large gear up a hill when you have 20 better options. Enjoy!

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Bob Forgrave
President, Flatbike.com

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425-985-6219

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