Setting Wheel Size on Bike Computer???

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Setting Wheel Size on Bike Computer???

Postby Raher312 » Sat Oct 09, 2010 10:51 am

I just purchased a Wireless Sigma 1200 Bike Computer at Dicks and for the life of me can not figure out how to set the wheel size. My tires are 29 inches by 2 and the manual does not have a size on the chart for that. Is there some magic formula I can use for the wheelsize input? My road bike was a piece of cake to set up because the metric measurements were right on the wheel. I tried going on the website and using search engines but had no luck. Please HELP!
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Re: Setting Wheel Size on Bike Computer???

Postby ryanw » Sun Oct 10, 2010 8:48 pm

I just laid out a tape measure on the ground and measured the length of one full rotation of the tire. I had to convert to metric but not a big deal. I know that it is not perfect because I seem to gain about 4 tenths of a mile over a 10 mile ride (I compare my distance against a friends Garmin). I just need to shorten the measurement up a little bit.
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Re: Setting Wheel Size on Bike Computer???

Postby robert t » Sun Oct 10, 2010 11:27 pm

you can't just role your tire ,and measure it,
you have to put weight or push down on the wheel,
to get the proper length.as if you were riding.
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Re: Setting Wheel Size on Bike Computer???

Postby Raher312 » Mon Oct 11, 2010 6:15 am

Okay guys once I get on my bike and roll the tire, what do I do with the number I come up with? Do I multilply that number by something or is that the number that goes into the wheelset setting on the computer?
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Re: Setting Wheel Size on Bike Computer???

Postby Intense1 » Mon Oct 11, 2010 8:11 am

Does your computer want a metric number? It's probably looking for millimeters. Take the distance in inches and Divide by .03937. Instead of putting weight on the bike and rolling, you could also just measure the outside diameter of tire, minus a quarter inch or so (for compression under weight) and multiply by 3.14". The answer will be the circumference of your tire.
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Re: Setting Wheel Size on Bike Computer???

Postby ericw » Wed Oct 27, 2010 12:13 pm

ryanw wrote:I just laid out a tape measure on the ground and measured the length of one full rotation of the tire. I had to convert to metric but not a big deal. I know that it is not perfect because I seem to gain about 4 tenths of a mile over a 10 mile ride (I compare my distance against a friends Garmin). I just need to shorten the measurement up a little bit.


Probably a little late of a post, but here's what I did: Marked the tire and started that mark over a crack in the driveway. Sat on the bike and went forward three revolutions and marked that point. Measured, divided by 3, converted to MM... I figured 3 rotations helped average out some of the error.

That's no help you your real question about entering it into the computer, though...
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