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help, please with determining wheel size(8 posts)

help, please with determining wheel sizestan_b
Jul 28, 2002 8:28 AM
I'm trying to determine to correct millimeter size of my 700x23 wheel so I can get an accurate reading for my computer.

The handbook lists 2124 for 700x25 but doesn't give a figure for 700x23.

I tried measuring the distance the wheel covers in one revolution and came up with the figure of 2112 millimeters.

Is this correct? I really want the exact figure so my times will be completely accurate.

Most accurate wayDrPete
Jul 28, 2002 8:42 AM
The best way I know to get the measurement is to have a buddy around, get on your bike with the tire inflated to riding pressure, and roll forward for one wheel revolution, using your valve or the label on the tire as a reference. Then measure the distance covered on the floor/ground.

My going rate for 700x23 is 2155...
Even more accurate waymja
Jul 28, 2002 10:34 AM
Scribe a line on floor of basement or driveway. Put a spot of grease on tire. Roll away along the line, until spot with grease contacts twice. Measure distance between grease spots.

Also heard of checking this measurement by heading to local 1/4-mile track and riding loops and correcting for any error encountered.
re: help, please with determining wheel sizecurlybike
Jul 28, 2002 10:56 AM
Inflate the tire that has the magnet for the computer to riding pressure. Place a piece of electric tape on the street where you want to start. Wrap a piece of tape around the same tire,Through the spokes and over the tread. Place the wheel with the tape over the tape on the ground. Sit on the bike with a friend to support you. Roll the bike and yourself until the tape on the wheel touches the ground a third time, 2 revolutions, Place a piece of tape on the street in line with the tape on the tire. Measure from the edge of the tape on the ground to the corresponding edge on the other piece of tape on the ground. If you only have an inch measuring tape multiply inches by 25.4 then divide by 2. This will diminish measuring error and give you the exact rollout of the wheel your computer is counting revs of. Your computer may us cm instead of mm, adjust down by factor of 10. Any other system of measurement will depend on manf. instructions, but all I have seen can be derived from this rollout.
re: help, please with determining wheel sizestan_b
Jul 28, 2002 11:33 AM
But isn't there just one size for 700X23? How can my measurement by 2112 and the other poster 2155?
re: help, please with determining wheel sizemja
Jul 28, 2002 12:17 PM
No, there is variation among manufacturers. And the other fellow's measurement may be inaccurate, or yours ...
Jul 28, 2002 2:04 PM
Mine (Michelins) run between 2096 and 2100 for 700-23 inflated to 120psi with a 175 Lb rider. There is a wide range of 23's with respect to circ..
re: help, please with determining wheel sizeSteve Bailey
Jul 28, 2002 12:23 PM
Even after trying all the assorted methods - my own uses a chalk line on the floor at the valve, etc... you can still get a different reading as compared to other brand of computer.

Do the roll out method and don't worry if you do a 50 miler and someone say's, "I only had 49.7".