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Author Topic: Wheel Size  (Read 2128 times)

al

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Wheel Size
« on: August 19, 2012, 09:35:56 pm »

I'm confused by the wheel size setting. Unfortunately the manual does not offer any explanation. I assume it is talking about the radius, and therefore I put in 29 inches (for a 700c road bike wheel).
The problem happens with the distance estimation during the workout (which I assume is calculated based on the wheel size). For example after I finished a group ride of 21.75miles it only showed about 7.6 miles on the device. When I uploaded the workout to Strava it showes the correct distance (it's a ride I used to track with my Phone's GPS so I know the distance well).

Why is it so far off? Am I totally off base by using 29inches?

Thanks
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al

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Re: Wheel Size
« Reply #1 on: August 19, 2012, 09:48:41 pm »

I think I answered my own question. I knew I was off by a factor of approximately 3 ( I calculated 2 * PI * Radius). Of course 29" is the diameter, so, it should be 3.14 * 29" as the wheel size. That is about right for my ride 21.7 / ~7  =~ 3.x

Of course you have to take into consideration the tire size. So this website has a little table that may help.

http://www.bikecalc.com/wheel_size_math

In any case, I haven't tested this yet. But is it correct?
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GS_TECH01

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Re: Wheel Size
« Reply #2 on: August 28, 2012, 10:49:50 am »

Hello al,

Welcome to the forums! Sorry for the late response. I'm still checking with our engineers about this. Will keep you posted.
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GS_TECH01

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Re: Wheel Size
« Reply #3 on: August 31, 2012, 11:57:36 am »

Per our engineers, the wheel size setting can be easily determined. Apparently, it's the circumference of the wheel:  Circumference = 2 x pi x radius = 2 x 3.14 x radius. Also, the most accurate way to get the wheel size is to manually measure the wheel as there's no table available that would be able to cover all the sizes of the wheels.

Let me know if you have any questions.
 
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Longjog @ GS-Sport-Servicecenter

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Re: Wheel Size
« Reply #4 on: August 31, 2012, 03:22:35 pm »

The best is to measure the distance on the ground when the wheel turns exactly one rotation.
Best regards
Longjog
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GS_TECH01

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Re: Wheel Size
« Reply #5 on: September 04, 2012, 12:30:13 pm »

Thanks, Longjog, for your additional input. Hope this helps out other forum members as well. Thanks.
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gerhard

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Re: Wheel Size
« Reply #6 on: September 05, 2012, 02:29:42 pm »

A good list available at Sheldon Brown, see group F
As longjog said, size may differ and you may get fractions of a percent better by measuring yourself.

http://sheldonbrown.com/cyclecomputer-calibration.html#notsize
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RochesterMTB

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Re: Wheel Size
« Reply #7 on: September 06, 2012, 10:50:47 am »

Even knowing the correct wheel size doesn't fix a big problem, its in rounded inches.  My wheel size came to 90.75 so I have to round it to 91 to be close but over a long ride my distance will be way off.  This should be changed to the industry standard (mm) so it will be as accurate as possible and easy to determine.
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foo_fighter

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Re: Wheel Size
« Reply #8 on: September 06, 2012, 03:46:59 pm »

You can enter it in mm by changing the units to metric(kilo/meters), then change back to Imperial(ft/miles) for the display.
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GS_TECH01

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Re: Wheel Size
« Reply #9 on: September 10, 2012, 02:00:17 pm »

Hello All,

Thanks for sharing your input. Much appreciated!
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mikek753

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Re: Wheel Size
« Reply #10 on: October 11, 2012, 12:54:26 pm »

hi,

what should I set to 580p for Felt Z5 that has 700c in Inches?
I checked for those links and calc tables, but got confused even more.
The 580P doesn't allow select a fraction, so it has to be rounded anyway.

thanks.
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Best Regards.
Mike.

gerhard

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Re: Wheel Size
« Reply #11 on: October 11, 2012, 02:10:43 pm »

hi,

what should I set to 580p for Felt Z5 that has 700c in Inches?
I checked for those links and calc tables, but got confused even more.
The 580P doesn't allow select a fraction, so it has to be rounded anyway.

thanks.
You need the tire size in addition to the wheelsize.
For instance if you have a 23x622 tire (or 700 x 23), enter 2097.
You cannot enter fractions, but the 0,0005 accuracy will take you far. The tire variation is larger than that.
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GS_TECH01

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Re: Wheel Size
« Reply #12 on: October 12, 2012, 10:59:17 am »

Thanks, gerhard, for the input.
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mikek753

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Re: Wheel Size
« Reply #13 on: October 12, 2012, 08:43:51 pm »

hi,

tnx for the reply.
I set as 83inch that's close to 2106mm
yes, I have 700x23 "normal" tire
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Best Regards.
Mike.

al

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Re: Wheel Size
« Reply #14 on: May 25, 2013, 03:48:54 pm »

Measured mine on the floor (700C, 23mm tire) it worked out to be almost exactly 2100mm or 84in. So that's what I put on the device. Thanks
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