Gear Calculator

 

Highlight this gear ratio:
Highlighting range: %

Wheel size:

Common rim sizes Choose rim size 27'' road rim 700c road rim 650b road rim 650c time trial/triathlon rim 29'' MTB rim 27.5'' MTB rim 26'' MTB rim 24'' road/BMX rim 20'' recumbent/Dahon/BMX rim 17'' Moulton rim 16'' other folding bike rim

Common tire sizes Choose tire size 56mm road tire 50mm road tire 44mm road tire 38mm road tire 35mm road tire 32mm road tire 28mm road tire 25mm road tire 20mm road tire wide road tubular narrow road tubular 1 3/8'' road tire 1 1/4'' road tire 1 1/8'' road tire 1'' road tire 2.125'' MTB tire 1.9'' MTB tire 1.5'' MTB tire 1.25'' MTB tire 1.0'' MTB tire

Picking a rim and tire from the menus above will get you in the ballpark, and it's good enough for simply comparing different sets of gear combinations. For accuracy, measure your wheel's actual diameter and enter it into the Wheel Size field.

Chainrings: Click a number to remove it

Cogs: Click a number to remove it

Crank arm length: Choose crank length 185 mm 182.5 mm 180 mm 177.5 mm 175 mm 172.5 mm 170 mm 167.5 mm 165 mm 162.5 mm 160 mm 157.5 mm 155 mm 152.5 mm 150 mm

About the gear calculator

Why should you specify which tire you're using? Typically, the wider a tire is, the taller it is above the rim. The predefined tire sizes above are derived from the Tire Radius column in the table at the bottom of Sheldon Brown's page about Gain Ratios. Note that Sheldon uses some different numbers in his own gear calculator (see below). All sorts of factors will cause estimates to vary: Tires of similar widths from different manufacturers will have different profiles, knobby tires are taller than their non-knobby counterparts, an overinflated tire squishes less than an underinflated one, a heavier rider squishes a tire more than a lighter rider, a worn tire will be a couple millimeters smaller. Use anybody's published figure as nothing more than a reasonable estimate.

To measure your drive wheel's actual diameter, put the rider on the bike and measure the distance one full revolution of the rear wheel travels. Sheldon Brown's website provides detailed directions. Take the resulting distance, convert to millimeters, divide by pi, and put that in the Wheel Size field, above. If you're short on space and don't need to be as accurate, put the rider on the bike, measure the distance from the ground to the exact center of the rear axle, convert to millimeters and multiply the result by two.

Manual measurement is also your only option if your bike has an old or nonstandard rim size. As with everything else bike related, Sheldon Brown's website provides a useful table of rim and tire sizes.

This gear calculator requires a modern browser and Javascript. If you do not have a compatible browser, I strongly recommend downloading the latest version of Firefox.

The following calculators also require Javascript:

• Sheldon Brown's Gear Calculator, which can also calculate gain ratio; a more precise metric of effort for distance, taking crank length into account. It also calculates combinations of cogs and internal hub gears.
• Junior Track Cycling's New Gear Chart, a very nice tool designed for track racers.
• The HPV Drivetrain Calculator can accommodate multiple sequences of gearings (up to five multigear linkages) and generate reports in a variety of ways. It probably provides the most extensive customizability, for detailed analyses and planning.
• The Bicycle Gearchart Calculator provides much of the functionality of this page, plus a rear derailleur capacity function and additional results formats.

Junior Track Cycling's old Gear Chart does not require Javascript.

Many of the above calculators were influences on the design of this one. Their respective designs make them better options for a variety of needs.