There are several gear inch calculators on the internet, but most are either setup for geared bikes or only allow you to do one ring and cog size at a time. Since we're not in love with any of them we figured we'd design our own. If you're an ambidextrous skidder check the box on the left, and if you're looking for information on what each value actually means just click on any of the "i" boxes below. Select multiple rings and cog sizes for cross comparisons and don't forget to choose a tire size if you want an accurate calculation of gear inches.
Gear inches offer a simple system for measuring bicycle gear values. Originally, gear inches represented the diameter of a high-wheel bicycle’s drive wheel. When chain-drive bikes came on the scene, the gear-inch calculation was adapted to accommodate:
(Chainring Teeth / Cog Teeth) x Rear Wheel Diameter (wheel & tire) = gear inches.
Gear-inches are useful because you’re given a numerical value for your specific setup compared to all others. Knowing your bike’s gear-inch measurement allows you to make better decisions when customizing your gearing.
Simply put, your gear ratio compares the number of teeth in your front chainring to the number of teeth in your rear chainring. For example, at 34-tooth chainring and 17-tooth rear cog have a 2:1 gear ratio.
Your gear ratio determines how many potential skid patches your tire will have. By simplifying the gear ratio to the smallest whole number equivalent, we find that the denominator gives us our total number of skid patches. A 34/17t set up amounts to a 2:1 ratio, leaving you with just one skid patch, meaning you’ll wear your tire out quickly. With a 34/13t ratio, you have 13 skid patches.