Forum

[Edward]

I use a Garmin Streetpilot 2610 sat nav that cost £15 on ebay.

[another Allan]

Regarding Mike's comments on bicycle speedo accuracy, I'm sure he has a point. I have one fitted, which I happen to have checked against my car speedo, and it's ok. At the price I paid for it, though, I put this down to good luck rather than accuracy of manufacture! Regarding car drivers preferring to believe their satnav over their car speedo, I would always do this (assuming it was a well-known brand of satnav.) I have never had a vehicle of any kind where the standard speedo did not over-read. My current car indicates 70 on the speedo when my Tom Tom says 67.

[Alan (Lancashire)]

Micheal , yes the cycle speedo,s ARE accurate , if the correct wheel size is calculated correctly, the difference between the cheap and the more expensive is down to "extras". the units work on a simple hall effect system , the same as used by millions of cars for ignition timing, you don't often see cars where the the spark happens at random? the internals of those units cost pennies to manufacture , BUT the tyres true circumference must be set. many years ago when fitting one to my avon shod bullet , I contacted Cooper tyres(avon) tech who replied. 3.25-19 - revs per km 497, rolling circ = 2.012m, rolling dia = 640mm

3.50-19 - revs per km 482, rolling circ = 2.075m, rolling dia = 660mm

90/90-19 - revs per km 512, rolling circ = 1.95m, rolling dia = 622mm

100/90-19 - revs per km 493, rolling circ = 2.02m, rolling dia = 646mm

so if you set the correct size THEY ARE ACCURATE