How to choose gears for climbs

1. Enter the current transmission

Open "Transmission range". Choose 1x or 2x, specify the front chainrings and all cassette sprockets. For 2x, both front chainrings are needed. If you use a preset, check it against the marking of your cassette.

Enter the ETRTO rim diameter, tire width, and cadence to calculate speed. Do not confuse the rim diameter of 622 mm with the outer diameter of the wheel. The same chainrings with different wheels give different gear ratios.

2. Read the light transmission

Gear ratio is the number of teeth on the front chainring divided by the number of teeth on the rear sprocket. For 40/52, it's approximately 0.77. The lower the ratio with the same wheel, the shorter the distance covered per pedal revolution.

Development — this path is in meters. The speed also depends on the cadence. The percentage range shows the ratio of the heaviest gear to the lightest; by itself, a large range does not say whether the lower gear is light enough.

3. Compare 40 and 36 teeth in one example

Set 1x, 40 chainring, and cassette 10,12,14,16,18,21,24,28,32,36,42,52. For a 622 ×45 wheel, the calculation will give about 1.72 m on the easiest gear. At 70 rpm, this is approximately 7.23 km/h.

Now change only the front sprocket to 36. The development will decrease to 1.55 m, the speed at the same cadence is up to 6.50 km/h. The ratio has decreased by 10%. This allows you to go slower with the same pedal rotation, but does not mean that the climb will require 10% less energy.

4. Use the lift calculation as a guide

In the lift block, specify the slope, the mass of the entire system — bike, person and things — and the desired cadence. FTP can be added if you know its actual value.

For the example above, at 12%, 85 kg and 70 rpm, the model shows approximately 220 watts with 40/52 and 198 watts with 36/52. In the second case, the speed is also lower. The drag coefficients in the model are fixed; ground, wind, grip and variable slope can noticeably change the result.

The signature "you will stop by" is the output of the model, and not a guarantee of passing a specific lift. Compare the calculation with your stable capacity and the duration of the site.

5. Check the remaining transmissions and compatibility

A smaller front chainring also reduces the heaviest gear. Check your speed in fast sections, steps between chainrings, and duplicates for 2x. If you change the cassette, look not only at the outermost teeth: the gaps also affect the convenience of cadence selection.

Before purchasing, separately check the drum, the largest chainring, and the capacity of the derailleur, the compatibility of the chain and the attachment of the front chainring. The calculator calculates the ratios, but does not confirm mechanical compatibility. For this, there is separate checklist.

Save the link to the calculation from the field on the page: this way you can show both options to the mechanic and return to the original values.