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Road tubeless technical question

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Road tubeless technical question

Old 12-02-14, 09:32 AM
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elcruxio
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Road tubeless technical question

Ok, so I use tubeless but on one of my local forums a discussion popped up where some of the posters are of the opinion that road tubeless is unsafe since a normal clincher rim cannot take the pressure of tubeless even though using a tube with higher pressures is completely fine...
I would like to get some opinions on this and maybe even someone well versed in pressure physics.
I mean, I don't know. Does having no tube in the rim cause so much stress on the rim wall? What if you use a latex tube? Is the risk still nullified by it?

The funny thing is that my 28mm tubeless tires have a max pressure of 6bar and 23mm tubeless tires would have a max pressure of 8bar. Still one can use a clincher up to 10bar with a tube and apparently a clincher rim should be able to take it. But 8 bar without the tube is out of the question.

I call shenanigans, but that is exactly the reason I'm asking. I'd like to know so if there in fact is a danger in tubeless I may plan my future rim purchases accordingly (oh please please be BS, tubeless rims are so expensive!)
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Old 12-02-14, 09:43 AM
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dabac
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Given that the (amount of) strength added by the tube is quite marginal, which would have been demonstrated IRL to anyone who has ever had a serious gash to a tire, or anyone who (in desperation) has used a very undersized tube in a significantly larger tire, I can't see how pressure alone would make any difference between tubed and tubeless.

MAYBE - just speculating here - something funny happens right at the seam where tire meets rim. Maybe with tubeless air is free to sneak in between bead and rim sidewall/brake track and cause a blowoff. Can't really bring myself to believe that though.
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Old 12-02-14, 10:55 AM
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Max tire pressures are determined by testing a number of tires on a "standardized" rim. Generally recommended pressure is about half the burst/blow off pressures testing found. But in real life the rims on any bike are not the "standardized" rim the tire company uses in their testing. We all know of tight or loose tire/rim seating... as one moves the same tire to another rim.

The other aspect of recommended tire pressures is that of marketing. There have been tires with absurdly high max pressures (like 140psi). I always assumed this was to claim a bigger number in an ad. (And I feel that this high a pressure actually reduces traction/tire contact patch area). So if for marketing perceptions a reduced recommended pressure is better and doesn't exceed the "half blow off" pressure then why would a company say otherwise? Andy.
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Old 12-02-14, 11:38 AM
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* Part of the benefits of running tubeless is to run lower pressure without worrying about pinch flats I thought.
* When mounting/seating tubeless tires, you often use way more air pressure than you would normally to ride.

I've converted 3 sets of rims to to tubeless without issue:

da 7800
velocity a23
hed belgium
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Old 12-02-14, 11:46 AM
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Are you using the Hutchinson setup, with a dedicated rim and tire combo?
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Old 12-02-14, 12:35 PM
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I have never experimented with converting standard clincher wheels to tubeless. All my experience has been with wheels specifically designed for road tubeless tires. When Hutchinson first introduced road tubeless tires, they had a lot of trouble with fit. We were a distributor for Hutchinson at the time and there were numerous returns of the Fusion2 tires because they often simply would not hold air. This often centered around poor fit because the tire beads were not always consistent. For tubeless to work properly, the bead has to lock into the channel formed by the bead hook and a ridge that runs along the edge of the bottom of the rim channel. Once this happens, there is an audible snap sound as the tire seats. Road tubeless beads stretch less than standard clincher beads and have to be very consistent in diameter to keep the tire seated. Because you can run lower tire pressure without fear of pinch flats, tubeless tires are very unlikely to come off the rim and an advantage is that if you do flat the tire remains locked into the rim for quite some time allowing you to come safely to a stop
Hutchinson corrected the fit problem, later road tubeless tires hold air well. Mine hold air just about as well as standard clinchers with butyl inner tubes, even without sealant

Last edited by alcjphil; 12-02-14 at 04:10 PM.
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Old 12-03-14, 08:07 AM
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dsaul
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I've been running tubeless tires on Kinlin XR200 rims for 3 years with no problems. The only problem I ever experienced in trying to set up a regular clincher rim with tubeless tires was on a Kinlin XR270, where the bead seat of the rim was too small in relation to the tire bead and required a ridiculous amount of tape to get the tire bead to seat.

A tubeless ready rim will have better flat tire retention, but I haven't seen any evidence that there will be any catastrophic failure on a non-tubeless rim.
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Old 12-03-14, 01:18 PM
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Under pressure, the tube conforms to the inside surface of the tire/rim assembly same as the air does in a tubeless assembly. There's no difference.
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