Another question about cheap speedo into cadence question.
I bought a cheap wireless speedo from lidl (£6.99) earlier in the week and im currently trying to use it as a cadence meter. I have a magnet on the left hand crank arm and the receiver on the chain stay with the display on the cross bar so i can see it by looking down. The possible problem is. I have measured the distance from the BB to the magnet (170mm) i have then multiplyed that by 2 and then multiplyed that by Pi. (170 x 2 x 3.1416) = 1068 rounded down. I have put that into the computer as the wheel size and im using KPH but the read out does not seemright? my comfortable cadence according to the computer is 55 but that number seems low?
i have been looking around online and they mention gear ratio's as well.
Am i missing something in the calculations?
Im not overly fussed as i can use the computer reading as a standard (55) but it would be nice to have the correct cadence.
Any help would be great