Tesco wired trip computer

[Bagpuss12]

I'm recently new to cycling so bought a cheap and cheerful Tesco wired trip computer. It works fine HOWEVER I know it is providing me with false readings in terms of speed travelled and length of journey. I no longer possess the instruction although I know how to use it but needed to know the following :
1) When the computer is reset I'm expected to put in a 4 digit code which is supposed to equate to the circumference of my wheel. Based on my wheel size of 26" I inputted the code 2166. Firstly, anyone know if this is correct?

2) I placed the sensor towards the bottom of my forks to ensure a reading. Presumably I would need the sensor more towards the outer of the wheel if its based on circumference?? I seem to remember last time I did this the wheel was to far away from the forks to gain a reading??

 

[Rohloff_Brompton_Rider]

The easiest way to measure circumference is,

1. Draw a line on the floor
2. Line valve with said line
3. Complete one revolution and draw a second line where the valve is
4. Measure the distance between the 2 lines
5. Enter the the measurement into your computer

Easy peasy. It doesn't matter where the magnet and sensor are, as long as they only pass once per wheel revolution. The computer just uses the measurement entered for its calculations everytime the sensor senses the magnet.

I hope that was explained well enough to be understood....

 

[Bagpuss12]

Brilliant, thanks very much. Hopefully now it'll be more accurate and tell me how slow I'm really going??

 

[Biker Joe]

Later that day:......................"I'm cycling 25 mph....................computer says NO"

 

[SatNavSaysStraightOn]

distance measure about also depends of tyre pressures and what you weigh plus what you are carrying on the bike at the time (so if you have a heavy pannier then it would affect it - we have seen this on tour) - ideally you should be on the bike at the time if you want it really accurate and take around 10 rotations, then make an average (using bromptonfp's instructions)

my 26 x 2.0 tyres on a cateye cycle computer are on "2055", on my OH's sigma cycle computer they tell us it should be "2075" for the same tyre size, so as you can see it varies a touch from computer make to computer make as well.

all that said 2166 sounds a rather high figure IME - but I am limited to cateye & sigma trips which over the course of a 50 mile ride are tying in with my Garmin Edge 200 and various maps to within a +/- 250meters of each other, so you alternative would be to ride a set route that you know is exactly a certain distance, see what your trip records it as and work back from there how far out you are and adjust accordingly.

 

[paul04]

My sister has got one of those Tescos trip computers, I set it at 2030 and it is more or less correct

 

[subaqua]

brompton FB has the correct way to do it - that way you get the accurate reading for your tyres and wheels not what the manufacturer guesstimated. oh and measure in mm not inches ........