Bicycle Gear Calculator - Cadence vs speed and power required for derailleur geared bikes
Cadence - the number of revolutions of the crank per minute
Cadence is the number of revolutions of the crank per minute, this is the rate at which a cyclist is pedalling/turning the pedals.Take a look at the Wikipedia article on bicycle cadence.
There has been much scientific research on optimum cadence. For most people a cadence of 60 to 100 rpm is a comfortable range, with some sources measuring maximum power at 85 rpm and others at 90 - 95 rpm. You can measure your own preferred cadence. Zip tie a cheap watch (or a speedo with a timer) to your handlebars and count how many times your pedals rotate when you are pedalling hard. Factors are the degree of fitness of the rider and the degree to which efficiency or peak power are important.
Use the chart above to choose your ideal gearing.
Assume that as far as possible you need to pedal in the green area (which you set to your cadence range) with max comfort and power in the region of deeper green.
Gear calculation
- At the high speed end, how fast do you want to be able to go with a cadence near your maximum? Can you produce enough power to achieve this speed, on the flat, uphill/downhill, and with a headwind / tailwind?
- At cadences lower than 60 rpm it is harder work to create a given amount of power. Sure, athletes can create high power at low revs but it is still less efficient than pedalling faster! So, at the low end do you have a suitable gear that you can pedal within your cadence range that will get you up a steep hill?
- Inbetween, have you enough gears to be able to pedal at all speeds and keep within your target cadence range. It is inefficient if when you reach your max cadence in one gear the change to the next gear takes you below your min cadence.
- For that gear set what gradient of hill you can climb given your preferred cadence, weight and power capabilities.
- What power is required to pedal at different speeds in different gears with and without a headwind.
- For each gear ratio; what speed could you achieve within your cadence range and how many gear inches does the gear equate to.
- For each MPH point - which gear combinations could you use at this MPH and remain within cadence range
Gear calculation input data
A figure of two watts (of power) per Kg of body weight is often quoted as a maximum sustainable power for a fit person. Athletes can produce figures much higher than this.The calculations take frictional losses (tyres, bearings, chain), air drag and energy to climb a gradient into account when calculating power requirements.
The calculations for air resistance with a headwind / tailwind (enter a negative headwind) assume the wind is not at an angle and not affected by objects such as buildings or hedges.
In the analysis screen you can change two constants:
K_{A} is a coeficient used in the formula that calculates air resistance:
Source Bicycling Science: 0.368 Roadster, Utility bicycle 0.245 Sports bicycle 0.182 Road racing bicycle Another source gives: 0.17 for a rider tucked into an aero position. K_{A} varies from 0.1 to 0.4. |
C_{R} is a coeficient used in the formula that calculates rolling resistance:
Source Bicycling Science: 0.008 Roadster, Utility bicycle 0.0053 Default quoted by many authorities. 0.004 Sports bicycle 0.003 Road racing bicycle |
Whilst every effort has been made to ensure the accuracy of the information on this website, mistakes are possible therefore use it at your own risk!
Bicycle trail, the virtual line where the steering axis intersects the ground relative to the tyres contact point with the ground. Measure size using wheelbase or effective top tube. Ensure your bottom bracket height is set correctly. Cadence vs speed and power and calories used for hub and derailleur geared bikes. Cadence is the number of revolutions of the crank per minute. Calculate gear ratios. Optimise chainring and sprocket sizes. |
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