Computer advice / solution

[BearPear]

Hi Guys,

I'll start by saying that I am a newbie here, so be gentle!

I have really been enjoying going out on my new bike (Trek ladies 7.2) and wanted to know how many miles I was doing so got a Raleigh ARC005 cycle computer.

The leaflet didn't include tire circumference for my bike so I looked around on the interweb and found that Sheldon Brown gave 2168 for a 700 x 35, but I also found that the Trek people say it should be 2197.

I went for the 2197 and set off. My route measures about 7.4 miles on hubby's 'puter, and on mapmyride it says it's about the same, but my new 'puter says 8.3! My husband started to do the maths finding the variance between the Trek and Mr Brown's measurements, but neither gives a result anywhere near hubby's bike and mapmyride.

So, does it seem that my computer is out, if two other sources practically agree? And if so, how do I get a reliable measurement to load into the machine (please don't mention using a tapemeasure and pi - if I'd known there was maths involved in my new hobby, I never would have signed up!)

 

[Lazy-Commuter]

This does involve a tape measure, but no pi* ...

Position the bike so the wheel is in an easily recognisable bit of its rotation (valve at the bottom or something), make a mark on the path next to the wheel, sit on the bike and scoot it along until the wheel's done one full rotation. Another mark on the road, measure the distance between the two marks and that's your circumference.

* you can eat the pi later if you wish.

 

[tyred]

If you have a flexible tape measure of the type tailors use, run it around the outside of the tyre.

 

[BearPear]

Hmm, that seems too easy! But, easy is good. I shall enlist some help from the husband and measure-up.
Thanks for the speedy replies.