Bike Computer Use With 27.5"

The industry is coming out with new riding formats and 27.5 looks like a keeper. Here's where you talk it over with other riders.
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Bike Computer Use With 27.5"

Postby TheLonePeddler » Sun Sep 11, 2016 1:49 am

Hi, new to forum. Looking into purchasing a new 27.5 mountain bike. My concern is setting the computers wheel value for 27.5. The owners manual has no value for 27.5. Would setting it for a 27 value result in an inaccurate reading? Thank you.
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Re: Bike Computer Use With 27.5"

Postby dddd » Sun Sep 11, 2016 7:39 am

It will always depend on the width/height of the tires mounted on the rims, but a 27.5" tire of a normal 2.1" width is very close to the diameter of a 27x1-1/4" tire. Both are about 27".

You can make a "roll-out" measurement of your tire's size to get the number that you would enter into your bike's computer, either in inches or mm.
Quoting one entry from another forum:
"Put a piece of tape on the floor, and align your valve stem with it. Then roll your bike one wheel revolution, and put another piece of tape on the floor aligned with the stem again. Then measure the distance from one piece of tape to the other. That is your wheel circumference."

I find a chart online that has a 27.5x2.1" tire at the same 2155mm as a 27x1-1/4" tire.
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Re: Bike Computer Use With 27.5"

Postby TheLonePeddler » Mon Sep 12, 2016 10:55 am

Cool. I'll give that a try when I get the bike and use my handheld GPS to verify accuracy. Thanks! 8-)
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Re: Bike Computer Use With 27.5"

Postby bikesRfun » Mon Nov 14, 2016 7:46 am

Whenever I install a new set of tires on my bike I do a roll out measurement,
so it doesn't matter if the tire is 20" or 29".
I've seen a slight difference in measurements between different tires of the same rim size.
I do the roll out, use a tape measure, convert to centimeters and enter in my bike computer.
It's the most accurate.

If you don't need very accurate as above, a smartphone GPS is fairly accurate.
I use an android app called Cycle Droid. It's free from the play store.
Go to settings and select Metric or English units, enter your weight etc, and you're good to go.
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