|   Initial bead-to-rim seal w/ UST | 34x20
Jun 6, 2002 5:35 PM | | [posting, now, in recent area, in addition to archives]
From what I've read, it seems to me the initial UST inflation to 60 psi should be held for 12 or even 24+ hours before letting the pressure down. The UST bead area is coated with very soft rubber, and I believe that a weak bond is formed [under ideal conditions] between the rubber and the rim. I suspect that leak-down is due more to bead-rim seepage that through the tire carcass.
All this augers poorly for a good field repair without a tube. I don't know how we will eventually solve that problem [to field repair well, without a tube].
I use a dilute mix of dishwashing liquid detergent, sprayed on, to mount the tire. Once this dries out, the "bond" begins forming [I suspect].
Using a mounting lube is good, I believe, because it allows the tire to slip [toward the rim sidewalls] as far as the UST designers planned it to.
My compliments, Singleminded, on the original post - very well done. I agree - the UST tires are nearly miraculous.
Larry in Kingston, Ont., with 1x1 Ute. |
| re: Initial bead-to-rim seal w/ UST | singleminded
Jun 8, 2002 1:17 PM | | You may well be right, but I hope not.
If leak down of properly seated tires is not due to porous tire carcasses then that suggests a fundamental flaw (though not a "fatal" flaw) in the UST design.
Making truly air-tight tires shouldn't be hard and one would expect to see them as UST tire manufacturers gain more experience.
But if leak down is going to happen anyway -- anytime you've failed to make a 24-hour-long quasi-chemical bond between the tire's rubber bead and the rim's perfectly-clean alloy -- then that seems to indicate a basic problem with the design. One would hope that fully engaging the bead with the rim should be enough, as that would allow for at least the possibility of a truly tubeless trail-side repair.
One reason to think you may be right has to do with a major difference between UST and automobile tires: the ability to mount by hand. It may be that auto tires avoid this leak-down problem only because of the tightness with which they mount on the rim -- so tight that it requires powered machinery to achieve.
If you are right, let's hope that a full solution can still lay with tire design -- perhaps via a thicker bead. |
| UST leakdown data: 3 weeks | 34x20
Jun 10, 2002 5:57 AM | | Dear Singleminded,
You have made very good points. My UST Pythons [with 5 oz Tubeless Slime] leaked down from 29 psi to about 25 to 26 psi over 3 weeks [not being ridden between races]. I don't think auto tires have any real criterium to be lightweight - hence they can afford a thick inner layer of sealing rubber in the carcass. We'll never see a practical tire approaching anything resembling truly air-tight. Very good point about auto tire bead fit - it sure is a tight fit.....
Larry [in Canada]. |
| UST leakdown data: 3 weeks | singleminded
Jun 10, 2002 8:26 AM | | Leak down of only 3-4 psi over three weeks is good enough for me! Tubed tires do about the same or worse, espec. with thin tubes. Even car tires lose air over time.
Based on your experience and what I've seen so far with my own UST tires, a porous carcass does seem to be the bigger issue. I slowed leak-down considerably with less than 2 oz of Slime per tire, and without leaving the tire at high pressure for an extended period. My recent experiment with 3-4 oz of a latex/water mix looks so far to be doing as well or better.
Some leak-down at a properly-seated bead is ok as long as it's only a few psi a week. That would mean that truly air-tight tires would be both: a.) no more hassle than tubed tires in terms of leak-down, and b.) repairable trail-side without tubes. Once repaired, all you would need is sufficient CO2 to get the tire to the initial 50-60 psi necessary for the bead to seat properly.
For the time being it seems that racers should still carry a spare tube, since installing a tube would be much faster than patching the tire.
But IF (not to beat a dead horse) there was a good sealant product that you could shoot right through the valve, both plugging the hole and adding air, then you might never need a tube at all. You'd probably bring a spare tube only on those trips where you're bringing everything but the kitchen sink -- stuff like spare rear derailleurs and chains.
The only product I've heard of that might qualify is the Michelin stuff, which my LBS said won't be available in the U.S. until at least September.
In terms of making a truly air-tight tire carcass: there's got to be a way. Sure, auto tires can be relatively much heavier than mtb tires with no performance problems. But you'd think that some kind of material or design or manufacturing technique could be discovered to make UST tires air tight without adding a lot of weight. After all, Latex may do it as an end-user-applied additive. |
| I should add... | singleminded
Jun 10, 2002 10:15 AM | | that Penzoil "Fix-a-Flat For Bikes Only" is a currently-available product that may do what the Michelin product claims to do. I haven't tried it yet, but I am keeping a can of it in my Camelback. It supposedly contains actual rubber, which seems like a good thing, and Mountain Bike Action recommended it (not that that's a super-credible endorsement).
btw, I picked up a pair of Continental Twister Pro UST tires. They look nice, don't feel super heavy, and -- interestingly -- seem to have a thicker, squishier bead than my Python's. Maybe Conti did that to help address leak down at the bead. I'll definitely post impressions once I give them a try.
Also, I probably should have noted from the beginning that my Pythons and CrossRocs may be first-generation UST products. They came on a 2001 Bianchi Grizzly, so presumably they were manufactured in mid 2000 at the very latest.
One other minor note that I keep forgetting to add: Why the @$&%#! does the rim of my front CrossRock have a blue tint to it? The rear rim is pure black and every other CrossRoc I've seen has been pure black. Weird.
-- Peter (a.k.a. Singleminded) |
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