Tolerance buildup

Ok, my $.025 (inlation adjusted!)

His method is not bad at all, just that the accuracy numbers are really bogus.

To start with, he used a 30' tape measure and measured to .010" That is about as good as you can get using scibed lines on plates with dicom spray. Measuring on the ground with rubber tires, I would be more comfortable with 1/8" or 1/4" or 10 to 20 times less accurate.

Next hit is the fact that the tape measure has some inaccuracy from National Bureau of Standards. They are good but I'd figure another 1/8" in 30'

3rd hit is the fact that the rolling diameter changes when you put weight on it. If I took out my mountain bike with the tire pressure down for off trail work, I'd expect to see almost 1/2" of deflection on a 15" outside radius. This example would be a full 3.3% error. If he is running the super skinny road tires at high pressure, it may be less of a problem but I'd expect this to be the biggest source of error. Automobile tire manufactuers give you the actual revs per mile adjusted for centrifugal force. Sample table at Last issue is that the slower speed to set up the track tends to let the bike wander a bit from a seriously straight line that you see when you are pushing along at full speed. 2' over in 100' is not a big error but it does add up.

Net: I'd expect that this method would be good for around .1% or .2% error with good attention to detail and road bikes with high pressure tires.

Cheeers!!

Doug G> Please comment on accuracies reported in this article on calibrating a bicycle

(Nice answer from Roy J)

Which is why I use a dressmaker's tape around the tire, enter it, and forget it.

Thanks.

Yours,

Doug Goncz (at aol dot com) Replikon Research, Seven Corners, VA

1100 original posts at:

Doug Goncz wrote: (Nice answer from Roy J) Which is why I use a dressmaker's tape around the tire, enter it, and forget it. ^^^^^^^^^^^^^ I agree. And, even assuming that all those impressive measures (pun accidental) to gain great accuracy are valid, what are you going to do with the bicycle, use it as a surveying instrument? After a ride, I usually say, "Well, I rode about so many miles today."

Rather than fumbling with a tape measure around the tire, I find that two chalk marks on the sidewalk one wheel revolution apart are easier. And if you area real accuracy freak, make it ten revolutions, and use a steel tape measure. (Be sure to take the temperature of the tape measure, and use standard tension on it.) :-)

After a ride I usually say, "Whew. I made it. How about a Coke?"

Yeah, that's the method in the book. Optical sensor detects tire valve passing fixed point and fires paint ball gun.I just took the wheel out, ONCE, measured it, and that was it.

I have one and I think it's in decimal feet. For a really small tire, in inch units, you'd make twelve revolutions and convert feet to inches.

Q: What is the most significant difference between a rectal thermometer, a basal ovulation thermometer, and a fever thermometer.

A: The taste!

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Buy a GPS and mount it on the handlebars. Download track to computer with G7to or, if you use (UGH!) Windoze, G7toWin. You get track, times and distances.

Ted