Wheel Fanatyk: Clinchers & Tubulars

[Chooey]

Interesting article by Ric Hjertberg discussing the different physics of both wheel systems: Wheel Fanatyk: Wheelbuilding Tip #16 - Clinchers & Tubulars

[Zen Cyclery]

Thanks for the post. This is a good article. Definitely learned some things here.

[fixednwinter]

I learned a lot from that article thanks for posting.
I am now, more than ever, glad to be on tubulars for the road

[thomas]

His closing statement made me think of Tufo tires. Bennies of a tubular with the mounting of a clincher. Yet they don't seem to have a good rep. (I've never tried them.)

[sk_tle]

I tried them. Don't really see the point, they ride like clinchers. Only good points are the lack of pinch flat and quick mount but they can't be repaired except with sealant and you need a complete spare tire if the sealant do not work.

[Bob Ross]

Fascinating article. However, the author makes one contention that I don't understand.

He writes:

A clincher tire puts inner tube pressure in direct contact with the rim. An average road clincher rim is 0.5" wide and presents a 77" length. Surface area equals 38.5 sq in. If air pressure is 100psi, then total pressure felt by the rim is 38.5 X 100 = 3,850lbs. This 2 ton force is trying to make the rim smaller and is great enough to elastically deform many metal rims more than 0.1" in circumference. This may not sound like much but it has a large and measureable effect on spoke tension. 0.1" circumference = 0.032" diameter, or 0.016" radius. This is nearly one full nipple turn. Imagine the loosening effect.

But earlier he writes:

recognize that the constricting force of the [tubular] tire is actually quite low. The tubular tire deforms to match the rim but does not subject it to enough force to cause a significant change in the structure. Example: at 100psi of tire inflation, a tubular wheel loses no spoke tension. The rim supports any constricting force from the tire.

Um... huh? I don't get why a tubular tire ...in essence, a sealed hoop-shaped cylinder... when inflated to 100psi doesn't exert any substantial constricting force on the rim, whereas the tube inside a clincher tire ...also in essence, a sealed hoop-shaped cylinder... exerts substantial constricting force on the rim when inflated to 100psi.

What is it about the shape or configuration of a tubular that minimizes or redirects those forces when inflated to identical pressure?

[ergott]

Tubular tires are self contained pressure vessels whereas an open tubular (clincher) would continue to expand if it weren't for the rim.

[dgaddis]

Tubular tires are self contained pressure vessels whereas an open tubular (clincher) would continue to expand if it weren't for the rim.

So the tubular is taking all that air pressure on it's own then. In other words, you can pump a tubular up to 100psi even when it's not mounted on a rim?

[fixednwinter]

So the tubular is taking all that air pressure on it's own then. In other words, you can pump a tubular up to 100psi even when it's not mounted on a rim?

Yup. Pic of CG Pave not mounted on a rim, 100psi

[ergott]

These are the reasons why it took so long to have reliable carbon clincher wheels on the market. The carbon fiber layup has to be designed in ways that are completely different to tubular rims.

[bikinchris]

What is it about the shape or configuration of a tubular that minimizes or redirects those forces when inflated to identical pressure?

In other words, the tubular tire is trying to expand in all directions at once and the clincher is mostly trying to rip the rim apart and press into the center of the spoke bed. You can test this on your own by measuring spoke tension difference between an uninflated and full pressure clincher wheel and then tubular wheel. The difference between the tension on a clincher should be larger than on a tubular wheel.

[thollandpe]

Tubular tires are self contained pressure vessels whereas an open tubular (clincher) would continue to expand if it weren't for the rim.

Not completely self-contained. The bias of the casing makes the diameter constrict with pressure (ditto for clinchers) as the section swells. That keeps them on the rim. And why the glue job is so important w/ low-pressure 'cross tires.

Fixed, how much did that CG shrink when pumped to 100 psi?

[Dorman]

Not completely self-contained. The bias of the casing makes the diameter constrict with pressure (ditto for clinchers) as the section swells. That keeps them on the rim. And why the glue job is so important w/ low-pressure 'cross tires.

Fixed, how much did that CG shrink when pumped to 100 psi?

They shrink. It may not be as much as a clincher and you would need a very accurate guage to get a definitive reading, but there is a slight spoke tension drop at 100 psi. And if you get super crazy with the pressure the whole thing could grow like a balloon animal negating all loss. None the less clinchers suck. Why are we defending ourselves?

[drietz]

These are the reasons why it took so long to have reliable carbon clincher wheels on the market. The carbon fiber layup has to be designed in ways that are completely different to tubular rims.

Who would've thought that it would take an expert wheelbuilder like yourself to finally pound this one into my slow mind?

Doh!

[fixednwinter]

The bias of the casing makes the diameter constrict with pressure (ditto for clinchers) as the section swells. That keeps them on the rim. And why the glue job is so important w/ low-pressure 'cross tires.

Fixed, how much did that CG shrink when pumped to 100 psi?

Hey thollandpe;

Didn't get a chance to measure it, but there is shrinkage there. As you mentioned, high pressure keeps the tub on the rim. According to the Kurata Thermodynamic Lab thesis, at 94psi (or above), a tubular will not roll off a rim - the tubular itself has expanded on its inside diameter, effectively gripping itself to the rim.

That's the tricky part with cross tubulars. Riding them properly means wickedly low pressures (far, far below 94psi), which means an improperly glued tire can indeed roll off. Zank's cross gluing method, with its multiple steps and the use of base tape, is essential to avoid this. My pal Jamie, who has been riding at the Elite Women's level in cross this season, used Zank's gluing method, and she's had no issues with rolled tubs.

[jbl]

I've been wondering what causes the spoke tension drop on clinchers with a tire mounted. The natural next question is whether the spoke tension guidelines from rim manufacturers account for this.

[Z3c]

[QUOTE=fixednwinter;450698]Hey thollandpe;

Didn't get a chance to measure it, but there is shrinkage there. As you mentioned, high pressure keeps the tub on the rim. According to the Kurata Thermodynamic Lab thesis, at 94psi (or above), a tubular will not roll off a rim - the tubular itself has expanded on its inside diameter, effectively gripping itself to the rim.

A few year back when Chris Boardman was still doing bike reviews for one of the Brit mags, he talked about how, after going up/down two mountain passes he decided to stop and check the wheels. Turns out the tires had never been glued..

[bikinchris]

I've been wondering what causes the spoke tension drop on clinchers with a tire mounted. The natural next question is whether the spoke tension guidelines from rim manufacturers account for this.

Well, the manufacturers are aware that spoke tension drops on an inflated clincher.

[suhacycles]

[QUOTE=Z3c;450737]

Hey thollandpe;

Didn't get a chance to measure it, but there is shrinkage there. As you mentioned, high pressure keeps the tub on the rim. According to the Kurata Thermodynamic Lab thesis, at 94psi (or above), a tubular will not roll off a rim - the tubular itself has expanded on its inside diameter, effectively gripping itself to the rim.

A few year back when Chris Boardman was still doing bike reviews for one of the Brit mags, he talked about how, after going up/down two mountain passes he decided to stop and check the wheels. Turns out the tires had never been glued..

Well, does this imply that even using Tufo tape is overkill? =)

Given the closed nature of tubulars does it really matter then to use a wider 23mm rim versus a 19mm one when using 22-23mm tires?

[El Chaba]

[QUOTE=suhacycles;450996]

Well, does this imply that even using Tufo tape is overkill? =)

Given the closed nature of tubulars does it really matter then to use a wider 23mm rim versus a 19mm one when using 22-23mm tires?

I say no....(to the second question)