[gero]

Hi,

My girlfriend just bought a new quintana roo tri bike. She got a cateye cyclocomputer for it. Her tires are continentals, size 32-571. In the documentation for the cateye there are two listings for this tire size -

23-571 - 26x1 (59) - 1913
23-571 - 26x1 (65) - 1952

In the chart, this is the only tire that has that number in the brackets - I have no idea what it means and can't find anything on the tire that corresponds to it. We've tried measuring the wheel ourselves and get a number nearer to 1970.

Does anyone know what that number in brackets means and which one I should be using?

Thanks

 

[ewitz]

Do a rollout

 

[lawrence]

Measure and use that

The numbers you find in the manual are averages. Each make of tire is going to be a few mm different in size. Put the right size pressure in the tire and then using a flexible tape, aka tailors tape, measure the outside of the wheel that the sender is going to be mounted. If you don't have a tape, then use string and measure that. Some say sit on the bike and then measure while the wheel is on the bike. I think the minute flex at one point in the tire is minimal. Think about the flex in that one spot, and it's only 1 spot because at any point in time when you roll the tire forward, it's flexing on only one spot, the spot that's touching the pavement. The rest of the tire immediately rebounds to the original round shape. The flex at that spot is minimal. Use your measurement.

 

[TurboTurtle]

The numbers you find in the manual are averages. Each make of tire is going to be a few mm different in size. Put the right size pressure in the tire and then using a flexible tape, aka tailors tape, measure the outside of the wheel that the sender is going to be mounted. If you don't have a tape, then use string and measure that. Some say sit on the bike and then measure while the wheel is on the bike. I think the minute flex at one point in the tire is minimal. Think about the flex in that one spot, and it's only 1 spot because at any point in time when you roll the tire forward, it's flexing on only one spot, the spot that's touching the pavement. The rest of the tire immediately rebounds to the original round shape. The flex at that spot is minimal. Use your measurement.

"I think the minute flex at one point in the tire is minimal. Think about the flex in that one spot, and it's only 1 spot because at any point in time when you roll the tire forward, it's flexing on only one spot, the spot that's touching the pavement."

That 'spot' goes all the way around when moving. The effective radius (and therefore circumference) is from the ground at the 'flat spot' to the center of the axle.

If you are going to measure, do a 'roll out'. Start with the valve stem at the bottom. Make a mark on the cement. Move one revolution with your weight on the bike until the valve stem is at the bottom again. Make another mark. Measure between the two marks. If you have enough room and a long enough tape measure, do multiple revolutions and divide the answer by the number you do.

TF

 

[TurboTurtle]

Hi,

My girlfriend just bought a new quintana roo tri bike. She got a cateye cyclocomputer for it. Her tires are continentals, size 32-571. In the documentation for the cateye there are two listings for this tire size -

23-571 - 26x1 (59) - 1913
23-571 - 26x1 (65) - 1952

In the chart, this is the only tire that has that number in the brackets - I have no idea what it means and can't find anything on the tire that corresponds to it. We've tried measuring the wheel ourselves and get a number nearer to 1970.

Does anyone know what that number in brackets means and which one I should be using?

Thanks

Cateye Cordless 2 manual:

26 x 1 (559mm) 1913
26 x 1 (650c) 1952

Looks like your instructions got cut off. A 650c is 571mm (559 is the 26" MTB rim), so I think that the 1952mm circumference would be the correct one. Better to measure, though. - TF

 

[alienator]

"I think the minute flex at one point in the tire is minimal. Think about the flex in that one spot, and it's only 1 spot because at any point in time when you roll the tire forward, it's flexing on only one spot, the spot that's touching the pavement."

That 'spot' goes all the way around when moving. The effective radius (and therefore circumference) is from the ground at the 'flat spot' to the center of the axle.

If you are going to measure, do a 'roll out'. Start with the valve stem at the bottom. Make a mark on the cement. Move one revolution with your weight on the bike until the valve stem is at the bottom again. Make another mark. Measure between the two marks. If you have enough room and a long enough tape measure, do multiple revolutions and divide the answer by the number you do.

TF

Yup. What Turbo said. An alternative to the "sit on the bike" roll out test is one where you roll out the bike w/out rider and then subtract 4mm for every tire revolution. This is a suggested method in Polar manuals. I gave it a shot to see how accurate it was...and it was pretty damned accurate, at least on 700x23 tires, inflated to 110 psi. Whatever rollout method you use, you should roll through more than one tire revolution. Doing so reduces measurement error by approximately 1/(number of revolutions). So if you roll through 10 revolutions, you can reduce measurement error to about 1/10 of a single revolution rollout. In any case, a rollout is much more accurate than using a tape to physically measure the circumference of a tire.

 

[jasonwells4]

When I try to set the circumference, it starts at 2096 and only goes up(stopping at 3,000) when you press mode... How do you set a number below 2096???

 

[Squidward]

Press the Start/Stop button.