The quick and dirty method you can use while you're riding is that 100rpm on 100" gear is 30mph, it's pretty simple from that to work out the unknown from speed/gear/cadence if you know the other two.
@gbj_tester started
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The quick and dirty method you can use while you're riding is that 100rpm on 100" gear is 30mph, it's pretty simple from that to work out the unknown from speed/gear/cadence if you know the other two.