MAY 31, 2005

    You wouldn't happen to have run into an easy schematic that explains gear ratio for bicycles. One that makes it both easy to understand and, more important, easy to remember.
    That is, when you’re in high gear, is it easier to get up a hill, or faster to get down one?

John Y.

    I find that gears confuse average folk like no other mechanical aspects of bicycles. Let’s see if I can keep from making things worse.
    First, what about this "high" and "low" gear stuff? One way to think of it: low = slow, high = spry (fast). (Lame, I know—but stick with me.) So whenever you should or must go slow, like when starting from a stop, going up a hill, or biking into a headwind, you use a lower-numbered gear. Whenever you want or have to go fast, like when going down a hill or biking with the wind behind you, you use a higher-numbered gear.
    Also, the inner gear (both front and rear) has the lowest number.
    If you wanna see all this, have a look at the section on gears in my book, Urban Bikers’ Tricks & Tips. As with everything in my book you’ll get it explained with pictures: how a bike’s chain looks on different gears, in different situations.
    OK, now let’s talk science. Many bikes have different sets of gears in front (part of what we call the chainring) and in back (part of the cassette or freewheel). Why would you want your bike’s chain on, say, gear 1 in front and gear 5 in back, or gear 2 in front and gear 1 in back? Answer: If you wanna go the slowest with the easiest pedaling, use the combination that gets you lowest gear ratio. (More on that in a second.) If you wanna go the fastest, use the combination that gets you highest gear ratio. For going at medium speeds use the combination of gears that ends up with gear ratio somewhere in between the highest and lowest.
    How do you know the gear ratio? You gotta use math. For each front gear and rear gear you have to count the number of teeth on the gear, stick that number into a computational table, and based on your bike’s rear wheel diameter either do some calculations or use the ones somebody else has done. All very esoteric, but shown pretty well on the GeRZ Web page.
    You might get a kick outta trying this on your bike: Find the gear ratio for the combination of your lowest front gear (the smallest one) and the lowest rear gear (the largest one). This tells you, more or less, how steep a hill your bike can climb easily. A gear ratio of 16 means you can pretty much go up a wall. In comparison, for many average bikes with three gears in front and seven in back the lowest gear ratio comes to around 21.

Mr Bike

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