Cheap Cycle Computer

[Klaus]

Got a cheap cycle computer via Ebay from Hong Kong, talk about cheap at £1.70 .... obviously I am not expecting top quality but just one question, how accurate are cycle comps? Instructions say to install sensor and magnet without any indication where on wheel/fork, i.e. how far in etc. But have to put in tyre number, i.e. 207 for 26".
Haven't managed to programme in miles/h so staying with km/h. One test trip showed 1.6 km which is near enough 1 mile. Did the equivalent journey with car (due to no through road on ride) and shows only 0.7 mile. It's probably optimistic to use car trip meter to validate cycle trip .... especially if I can't go over the same route.
And anyway, I take the computed numbers with a pinch of salt and round down which is probably just as accurate.

 

[Arch]

Are you working from a chart of numbers to input for each wheel size? This may be limited, since there are many different tyres to fit a 26" wheel, with slightly different circumferences. For the most accurate reading, you measure the wheel circumference, and input that in mm (assuming your computer works that way, and isn't just using a code for wheel size.). (to be really anal, you measure a revolution with you sitting on the bike, because your weight deforms the tyre slightly).

It doesn't matter how far up the fork/spoke the sensor and magnet are - they just count the revs and the computer does the maths according to the circumference you've told it.

And to calibrate it, you really would have to do the exact same trip. In fact even then it won't be exact, because on a bike you will weave from side to side a certain amount, that you won't in a car.

On the other hand, as you say, you can use the readings as a rough idea, and not get too hung up about it.

 

[Klaus]

Yes there is a chart in the instructions, I'll see how that compares to the actual measurement. But as you say there will be variation due to weight and riding.

 

[Muddyfox]

on a bike you will weave from side to side a certain amount, that you won't in a car..

Have you been following me Arch ?

The garmin edge is probably one of the best bits of cycling kit i've ever bought ... accurate to 14 feet apparently

Simon

 

[sparrow101]

your car trip computer is probably less accurate than the bike one as the speedo generaly over reads by 4mph

 

[Muddyfox]

your car trip computer is probably less accurate than the bike one as the speedo generaly over reads by 4mph

I agree with that ... my car speedo is different to the speed on my Sat Nav by 3mph

Simon

 

[ASC1951]

I agree with that ... my car speedo is different to the speed on my Sat Nav by 3mph

Well I don't.

Cars do not use the same mechanism for measuring speed and distance. It is quite common for speedometers to over-read slightly (subject to MoT parameters) but odometers are normally very accurate.

My bike and car odometers are closer than 99%.

 

[Klaus]

Anyway, whatever the technicalities, my cheapo computer told me I'd done 14.3 km today around town which is roughly 8 miles. I am getting the hang of gear combinations so I can actually do long stretches without getting off at some difficult bits....

 

[Muddyfox]

Well I don't.

Cars do not use the same mechanism for measuring speed and distance. It is quite common for speedometers to over-read slightly (subject to MoT parameters) but odometers are normally very accurate.

My bike and car odometers are closer than 99%.

If this is the case then i stand corrected

Simon