Originally Posted by MrCjolsen

If my speedometer say's I'm going 19.2 mph, I expect that I'm actually traveling at 19.2 mph and not 19.0!

I get really pissed when I find out it's wrong. (really, I do).

So now let me describe how I calibrate my computer. Tell me if this is accurate or not.

I set it according to the instructions, Sheldon Brown's numbers or even the default number it comes at. Just to get a baseline.

Then I ride the bike for a few miles over a course that I've measured on Google Earth. I generally use the Yolo Causeway because it's almost perfectly flat and straight and 3.11 miles from levee to levee. It's also on my way to work. As I ride, I try to stay as straight and centered as I can.

Then I take the distance my computer reads and divide that number by the distance I rode. Then I multiply that number by whatever number I told my computer was the size of my tire.

I did this today, actually. I had entered 2136 as my tire size. I rode the causeway. At the other end, it said I rode 3.15 miles. 3.11/3.15=0.99 .99x2136=2115 (my new wheel size).

Originally Posted by JanMM

Ow! My head hurts...........