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Tire circumference

Old 08-03-20, 06:39 AM
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Richard80
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Tire circumference 700 x 25

I can use some help with finding the right tire circumference to set in my Wahoo app.
My tire is a "Bontrager R1 700 x 25 / hard-case lite".
When I choose a "700 x 25c" in my Wahoo app, it sets a circumference of 2.105 millimeter.
However, when I measure the tire circumference manually, it is about 2.130 millimeter and according to the Wahoo app I have to choose "700c Tubular".
My question is: What is the difference between "700 x 25c" and "700c Tubular"? And what is the right size in millimeters to use?

Last edited by Richard80; 08-03-20 at 06:47 AM.
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Old 08-03-20, 06:57 AM
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I think tubular is a tire type that has an innertube sewn into the tire and glued to the rim.

The typical tire most people use is called a clincher. The R1 is a clincher.

Tubeless is the other type, sometimes called TLR.
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Old 08-03-20, 07:06 AM
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Tires squish and their effective diameter shrinks, once weight is applied. If you're real picky on a bike that you actually ride on the road, you can get a helper and roll down the driveway for 3-4 revolutions and measure the total.

On a trainer, it's not that critical, since it's all make believe riding. These days, I just put in 2105mm for my 25mm tires and call it good. If you're training seriously, it's more about time and power, not miles.
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Old 08-03-20, 07:17 AM
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Originally Posted by Richard80 View Post
I can use some help with finding the right tire circumference to set in my Wahoo app.
My tire is a "Bontrager R1 700 x 25 / hard-case lite".
When I choose a "700 x 25c" in my Wahoo app, it sets a circumference of 2.105 millimeter.
However, when I measure the tire circumference manually, it is about 2.130 millimeter and according to the Wahoo app I have to choose "700c Tubular".
My question is: What is the difference between "700 x 25c" and "700c Tubular"? And what is the right size in millimeters to use?
Those are some really small tires - must be awesome for low rotating weight.

I assume that you've got a wheel sensor on the bike, if you're asking about this? Why not just let the Wahoo auto-calibrate?
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Old 08-03-20, 07:21 AM
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Originally Posted by WhyFi View Post
Those are some really small tires - must be awesome for low rotating weight.

I assume that you've got a wheel sensor on the bike, if you're asking about this? Why not just let the Wahoo auto-calibrate?
Or he could just do an actual roll-out measurement.
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Old 08-03-20, 08:36 AM
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Richard80
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Originally Posted by WhyFi View Post
Those are some really small tires - must be awesome for low rotating weight.

I assume that you've got a wheel sensor on the bike, if you're asking about this? Why not just let the Wahoo auto-calibrate?
How do I auto-calibrate on Wahoo? The only option I see is to set the wheel size to "Automatic". From a review on Youtube I understood that Wahoo is basically guessing your wheel size.
So I thought setting it manually is a more acurate choice.
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Old 08-03-20, 08:48 AM
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Originally Posted by Richard80 View Post
How do I auto-calibrate on Wahoo? The only option I see is to set the wheel size to "Automatic". From a review on Youtube I understood that Wahoo is basically guessing your wheel size.
So I thought setting it manually is a more acurate choice.
Yeah - Automatic is the setting that you use. Are you recording rides using the phone app or a Wahoo head unit? If a head unit, saying that it's "guessing" is shortchanging things a bit - it's using GPS and historical ride data to calibrate and adjust. Phones have a better chance of being all over the place, though.
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Old 08-03-20, 09:31 AM
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To measure tire circumference, first check your tire pressure. Then stretch a tape measure out on a suitably long bit of floor, street, or driveway. Put the valve stem at the end of the tape, a couple inches away from it. Sit on the bike. Roll forward, pushing with you feet. Check the measurement when the valve stem comes around again. To make that finer, ride a long known distance, a RWGPS route for instance. Modify your number by the percentage difference between the known distance and your reading.
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Old 08-03-20, 09:48 AM
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With the disparity you are concerned about.... if I didn't move a decimal the wrong way, over the course of 100 miles (160.9 kilometres) you will be off by 29.4 feet (8.97 metres). Do you need more accuracy**********???

Measuring the wheel circumference off the bike will be a disparity from doing a roll out because the tire isn't that circumference when weight is it giving it a smaller diameter. Is the difference material? Probably not.

The only thing I might say about auto calibration is that it might be that one day the auto calibrate gets flaky. Maybe for GPS satellite interference with environmental factors. And it might be that it goes flaky when you are doing the best most important ride of your life. Murphy certainly must have a law about that!

I had it happen exactly once. A long long time ago. I'm pretty sure they have built in some additional code to look for such as I've not seen anyone complain about it like I was seeing ten years ago.
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Old 08-03-20, 10:11 AM
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Originally Posted by WhyFi View Post
Those are some really small tires - must be awesome for low rotating weight.
It's just the logical extension of the latest "small wheels are just as fast" theory.
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Old 08-03-20, 10:18 AM
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Originally Posted by tomato coupe View Post
It's just the logical extension of the latest "small wheels are just as fast" theory.
But, man, do you feel all of the bumps on the road.
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Old 08-03-20, 10:42 AM
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Originally Posted by Carbonfiberboy View Post
To measure tire circumference, first check your tire pressure. Then stretch a tape measure out on a suitably long bit of floor, street, or driveway. Put the valve stem at the end of the tape, a couple inches away from it. Sit on the bike. Roll forward, pushing with you feet. Check the measurement when the valve stem comes around again. To make that finer, ride a long known distance, a RWGPS route for instance. Modify your number by the percentage difference between the known distance and your reading.
Same idea, but draw a heavy line with chalk. Ride over it and keep going.. the tire should pick up some of the dust and lay it down again. Measure distance between the 2 lines.
Or..? Have someone sit on your bike? Measure from your axle center to the ground (radius of wheel). C = 2 pi R.. or 6.28 x Radius (measured).
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Old 08-03-20, 12:36 PM
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Originally Posted by WhyFi View Post
Yeah - Automatic is the setting that you use. Are you recording rides using the phone app or a Wahoo head unit? If a head unit, saying that it's "guessing" is shortchanging things a bit - it's using GPS and historical ride data to calibrate and adjust. Phones have a better chance of being all over the place, though.
I use the head unit to record rides. Based on your clear explanation, I think it is best to use the automatic setting. Thanks a lot.
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