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Old 08-05-08, 02:16 PM   #1
thebarerider
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Different tires on bike, computer question

Will having different sized tires (700x28 front, 700x32 rear) screw with the way my computer judges miles and mph? It seems to judge properly, but I wondered if anyone had any experience with this. The computer reads from the front tire and I set the wheel diameter as 700x28.
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Old 08-05-08, 02:38 PM   #2
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No, air pressure will have some effect on exact rolling distance.
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Old 08-05-08, 03:55 PM   #3
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you're ok. it only cares about the diameter of the wheel with the sensor
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Old 08-05-08, 05:09 PM   #4
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you're ok. it only cares about the diameter of the wheel with the sensor
That's what I thought. Thanks
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Old 08-06-08, 07:37 PM   #5
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What is the calculation to convert 700C to inches?

I'm coming from a MTB background with 26" x X wheels so I'm used to the 26" sizing. I also have a road bike with 27 1/4 I think for the wheel sizing so I'd like to know how to calculate that as well. Thanks in advance.
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Old 08-07-08, 01:06 PM   #6
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@ Zero:

What to you need to calculate? The wheel size?
All you need to do is look at the instructions for your cyclo-comp. you need to tell your comp what your tire size is. Every tire has a 4 digit number on the side wall. You need to input this number into your computer.
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Old 08-10-08, 12:32 PM   #7
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@ Zero:

What to you need to calculate? The wheel size?
All you need to do is look at the instructions for your cyclo-comp. you need to tell your comp what your tire size is. Every tire has a 4 digit number on the side wall. You need to input this number into your computer.
I understand how to program a bike computer. I was talking more on the wheel size conversion to inches then how to program that to the bike computer. Sorry for the confusion there.
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Old 08-10-08, 06:15 PM   #8
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25.4 mm = 1 inch.
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Old 08-10-08, 06:19 PM   #9
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Quote:
Originally Posted by Elyone View Post
@ Zero:

What to you need to calculate? The wheel size?
All you need to do is look at the instructions for your cyclo-comp. you need to tell your comp what your tire size is. Every tire has a 4 digit number on the side wall. You need to input this number into your computer.
And use Max psi.
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Last edited by 10 Wheels; 08-18-08 at 06:15 AM.
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Old 08-10-08, 06:59 PM   #10
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Better still, make a chalk line on the ground and line the valve up with it. Sit on the bike and roll forward until the valve comes to the bottom again. Make another chalk line and measure the distance between them. That's a more accurate method than relying on the printed instructions. Actually it's in the instructions for my Sigma.

I recently changed from a bike with 700 x 35 tires to one with 700 x 28s. The latter had a rolling distance 50mm shorter. Not sure that would translate to over a longer ride.
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Old 08-10-08, 07:02 PM   #11
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I understand how to program a bike computer. I was talking more on the wheel size conversion to inches then how to program that to the bike computer. Sorry for the confusion there.
Just use Google, e.g., type in "convert 28 inches to millimetres" and up cames the answer: "28 inches = 711.2 millimeters".

Google does a lot of useful calculations like that.
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Old 08-15-08, 06:43 AM   #12
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I have 2 sets of tires/ wheels for my mtb, and at the same pressure, they have different "rollout" distances (chalk line method). My "trail" set is smaller in diameter, so it ends up being almost 10% off in distance when they are at the "riding pressure". Only way to know for sure is if you do the rollout measurement.

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