Originally Posted by Rockadile
I have a Schwinn 17 Function Cycle Computer. I set the number to the size tires I have and I rode along side my friend with a Camry and a digital ODO. We tried 3 times and in all cases I was a good 50 yards behind him at the end of 1 mile on a straight road.
#1. First of all who is right, maybe the car ODO is off?
#2. 2nd of all I guess I want to add some distance so I input into the computer that the tire is smaller than it is in real life, then I will be going further before it says 1 mile has ticked off and I should be even with the car right?
Contact PTI sports (the actual maker of the computer, it's just schwinn branded), and get the actual formula.
Their formula is actually defective though, and will still give you wrong readings. Use it as a starting point though, as it gets you closer.
I ended up calibrating my schwinn by writing down what measurement I used, then doing a planned 20 mile ride (exactly 20 miles...this was verified by 4 other friends with their computers doing this same ride....20miles from the drop-off at my apt building and ending there...I even marked a spot with water washable paint as a start/stop point). I compared the results week by week, until I had a perfect 20 mile readout on it.
Next time around, I'm buying a cateye computer.