Cycling Computer and Tire Size

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2009-03-13 2:09 PM

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Subject: Cycling Computer and Tire Size
i bought a cycling Computer that the program tire sizes go from 700 x 25 and then to 700 x 28. My tire size on my bike is 700 x 26......If i program the computer for the 700 x 25 size will it make that big of difference in my readout? If so...suggestions on how to make it the most accurate?


2009-03-13 2:25 PM
in reply to: #2016262

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Pro
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Subject: RE: Cycling Computer and Tire Size

roll it out. Mark the distance on the floor that your tire makes (ideally under pressure) in one full revolution. Then measure it, and input it.

 

2009-03-13 2:32 PM
in reply to: #2016262

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Subject: RE: Cycling Computer and Tire Size

Actual measurement could work, but I'm too lazy and have never been able to do it right. If you wanted to, you could interpolate to get the circumference for the 26. Cateye's site gives the circumference for the 25 and the 28 as 2105mm and 2136mm, respectively. Interpolation table then would look like this:

252105
262115
272126
282136

So use 2115 for the 26.

2009-03-13 2:52 PM
in reply to: #2016262

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Woodstock
Subject: RE: Cycling Computer and Tire Size
On my wheel size chart it shows the 700 x 25c to be: 2146 and the 700 x 28c to be: 2149.....so would that mean the 26c would be: 2147???? Sorry I am new to all this.
thanks
2009-03-13 2:54 PM
in reply to: #2016422

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Subject: RE: Cycling Computer and Tire Size

haymar2 - 2009-03-13 2:52 PM On my wheel size chart it shows the 700 x 25c to be: 2146 and the 700 x 28c to be: 2149.....so would that mean the 26c would be: 2147???? Sorry I am new to all this. thanks

Yeah, 2147, but if they're that close I wouldn't sweat the difference.

2009-03-13 3:06 PM
in reply to: #2016262

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Woodstock
Subject: RE: Cycling Computer and Tire Size
Thanks

2009-03-13 3:10 PM
in reply to: #2016262

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Elite
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Subject: RE: Cycling Computer and Tire Size
I say just don't trust the chart at all.  I put in what my chart suggested and after doing a 65km ride, the computer and google maps disagreed on the distance by over 1 km.  When I actually rolled the wheel and measured it and adjusted to the right number, the computer and maps were within 100 meters of each other.  If you are at all picky about how far you go and what your speed is, measure the wheel.
2009-03-13 3:49 PM
in reply to: #2016471

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Subject: RE: Cycling Computer and Tire Size

axteraa - 2009-03-13 3:10 PM I say just don't trust the chart at all.  I put in what my chart suggested and after doing a 65km ride, the computer and google maps disagreed on the distance by over 1 km.  When I actually rolled the wheel and measured it and adjusted to the right number, the computer and maps were within 100 meters of each other.  If you are at all picky about how far you go and what your speed is, measure the wheel.

Is there some reason you think google maps is more accurate than your computer? One kilometer out of 65 is a mere 1.5% margin of error.

2009-03-13 5:38 PM
in reply to: #2016582

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Elite
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Subject: RE: Cycling Computer and Tire Size
the bear - 2009-03-13 5:49 PM

axteraa - 2009-03-13 3:10 PM I say just don't trust the chart at all.  I put in what my chart suggested and after doing a 65km ride, the computer and google maps disagreed on the distance by over 1 km.  When I actually rolled the wheel and measured it and adjusted to the right number, the computer and maps were within 100 meters of each other.  If you are at all picky about how far you go and what your speed is, measure the wheel.

Is there some reason you think google maps is more accurate than your computer? One kilometer out of 65 is a mere 1.5% margin of error.

Well at the time, I didn't know which was right and which was wrong until I actually measured the tire size.  Once I did that and it was virtually identical to the maps, that pretty much settled it.  

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