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UST's Burping. Whats the cause?
Test rode a bike awhile back with some ZTR wheels, and Specialised ground control tyres.
Apart from the tyres being extremely sketchy when pumping hard or landing, the biggest thing that killed my ride was air burping out the rear. Happened a few times up Rocky, twice down Mercury when I railed a corner hard, and again when I popped off the end of that log. Both times the tyre collapsed awkwardly and I nearly stacked. Ended up stopping 3 times to pump. All this and I was running more pressure than my XT and Maxxis LUST combo, which have never leaked any air.
So im trying to figure out what actually causes this?
Is it purely tyres or rims, or a combination.
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Firstly you need UST rims and UST tyres (no doubt others will argue - I'm just saying in my experience "tubeless ready" is not the same).
Then, the rim needs to have enough width for the tyre, and the tyre needs to be the right tyre for your riding style. If you are "landing" and "railing berms" then you shouldn't be using an XC set-up. Same if you are a heavier rider and/or riding well fast.
ZTR rims go right up to downhill, but many models are just for XC - you don't specify what you were using.
But, in my experience, you can have all that right and still some tyres will randomly burp
See following thread which includes comparison from Specialized.
http://www.socaltrailriders.org/forum/workshop/4...
Sounds like they were 2Bliss without sealant from the burping, but that would seem kind of reckless for a test bike to be offered like that. Maybe the sealant had dried out?
FWIW - probably a combination IMO. Nice read with some thoughts here: http://www.pinkbike.com/news/Tech-Tuesday--Wider...
What was rim model and width and tyre size? ZTR Alpine, Crest or Arch rims, are 5mm or more 'narrower' than Flow EX. Ground Controls (which of the 5 types, the sport isn't UST) are 1.9 to 2.3 width - however older versions were, I believe, 2.2 wide.
Given how hard you ride, and depending on which combination you were on, burping may be an expected outcome.
I've found non-tubeless Maxxis needs to be around 30psi, anything less tends to burp. UST you can dip into the mid-20s OK, but not much lower.
Schwalbe is fine (on the front at least) at mid-20s (NN 2.25), rear I tend to run high 20s-low30s.
Rubena 3-in-1 tubeless ready needs to be 30psi or it *will* burp quite easily.
The common factor seems to be the thinner and more supple the wall, the more pressure you need to run to keep it on.
Has anyone had any experience with these wheels?
I am 178 pounds (81kg), obviously over the Max Recommended rider weight, but for use only on race day is it worth the risk?
when its a race your bike needs to be 100%.....nothing on your bike should be left to chance in a race if you are serious. Sure you might save some precious weight. Racing isnt about absolute min weight. A lot of races have ben lost because of bad mechanical management. but not so many races have been won because of added lightness.
To put in a competitive race performance, you first have to finish the race.
DNFs don't count.
Running tubeless, does higher air pressure help to avoid 'holes' in the sidewall
Same as higher pressures help to avoid pinch flats in tubed tyres
We're talking small tears/ holes that the sealant should seal (but have found that it doesn't always)
So if I'm running 25psi, am I more prone to these ' tears' than if I'm running 30psi?
"If you are "landing" and "railing berms" then you shouldn't be using an XC set-up"
What.
Especially on Mercury St. What??
Put some stans No-tubes race formula liquid in there, about 1 of the red measures full will do it. Then run enough pressure - you should be using more pressure than you would with a tube type setup - common mistake people use lower pressure.
wha? isn't the main reason for running tubeless that it allows lower pressures (and therefore lower rolling resistance and more traction) without the risk of pinch flats?
No point in going to all the hassle if you need to run higher pressures! You'd just run tubes.
Tubeless lets me get away with 5-10psi less. Big improvement in grip.
I think the question is ,that if he runs more pressure in tubless, does it reduce the chance of ripping the sidewalls.
I think yes however that really needs to be qualified as there is a lot of compromising to be thought about.
a propper UST tyre has thicker sidewall. They are pretty hard to slash. But its posible. If you do slash it.....Its not bad management so much but just bad luck. Thats why you carry an inner tube. In some cases the hole is small enough to be closed by tyre sealent. When you have higher pressure in your tyre its harder to slash. But your compromise is less grip.
More grip is my own priorety as there is a pretty small chance of ripping the sidewalls. Obviously too little pressure might go the other way & you start burping the tyre.
When you run tubless ready, your question probably becomes more relevant. I've run standard TL on the front for 12 mths very successfully. Eventually the sidewall just packed it in. But they lasted a solid 12 mths. But tyre pressure is more about not burping the tyre rather than protecting the sidewall so pressure is always a little higher. Standard sidewalls on TL ready are wafer thin. After having ridden them competetively & they served thier purpose I feel they are not worth the risk though. Especially not on the rear wheel. No matter what pressure you decide to run in a tubless set up.
So if you are concerned about protecting your sidewalls....get propper UST ones with the weight penalty. You can run fairly low pressure with a very small chance of ripping it.
Thanks Stan
I've managed to 'flat' 2 specialized 2bliss rear tyres running around 28-30 psi
One a Captain and the other a Purgutory - both with holes in the sidewall
Really liked the Purg, but have canned it in favour of a non tubeless Ardent folding bead
It's light and grippy and run it at about 32 with no probs so far
When I was running tubes I used pressures around 38
So I think I may stick with around 32 for the rear and a tad less for the front (standard Nevegal runs like a dream)
Think I may need a proper pressure gauge as the bike pump one is a bit hit n miss i reckon
re: When you have higher pressure in your tyre its harder to slash.
I have seen a comment from Jason English on this subject that suggested that lower pressures would result in fewer sidewall slashes. That rationale was that lower pressures allowed the tyre to deform easier and therefore the contact between the rock/stick/etc and the tyre would be lower force and cause less damage to the sidewall. I can see some logic in the theory as its harder to burst a partially inflated balloon with a pin than a fully inflated balloon.
So I am not sure there is a definitive conclusion about tyre pressure and sidewall damage. Did you have any specific reason why you think higher is harder to damage?
right......OK. That is interesting I can see that logic as well.
MMM......yea that would make it far more complicated. Bit like the bed linnen hung up to dry when you shoot a 22mm at it The bullet it will most likely fall to the ground once it hits the linnen but the 22 will probably go happyly straight through a piece plywood.
Interesting. Thats getting far too complicated with tyres for me. I think I'll stick to my air pressure for grip & stick with tyhe snakeskin & UST tyres for protection.
I always thought the gauge on my track pump was pretty accurate until I got a digital gauge.... what I thought was 20F-22R was apparently 17F-19R.
The grip and reliability still feel the same but I'm inclined to be more cautious now I "know" how low the pressure really is..... funny thing, the mind?
Andy Bloot: I've run 2bliss Purgatory(F) and Captain(R), both S-Works, on Roval rims at 25psi for couple of years in WA and never had a tyre burp, wall rip or puncture (except for a nail picked up in the midle of nowhere! which Stans sealed). Maybe it's the terrain I ride and maybe i don't hit things hard enough and I'm a realtive lightweight at under 70kg. But I've run them lower with no probs. So probably an example of tyres for courses, terrain and style.
Slow pup - what tyre gauge do you have - looking for one myself so interested in the make of yours?
Agree its complex.
I am with you and just stick to choosing a wide tyre and a lowish pressure and running with that. Never had a tubeless tyre burp or a puncture caused by a wall rip. The worst sidewall problem I have had was a full UST that had a big mark in the sidewall that rippled the sidewall and clearly broke some of the threads but didn't leak.
I have had a few punctures through the tread but have managed to eventually seal these after a bit of shaking to get the stans into the hole.
With our sydney conditions I run snakeskin or full UST on the rear but have been able to get away with TL ready on the front.
Could well be my fat A causing the troubles
I have had so much trouble with Spec tyres for some reason
Tore 3 all with plenty of tread left, all tubeless that I now run with tubes on other bikes
Maxxis and my beloved Nevegal's seem to be relatively unproblematic
Of course now that I said that...
Interesting about the lower tyre pressure = less flats
Never thought of that one, but does kind of make sense
Be interested in that tyre gauge as well Slowpup
Andy, might just be bad luck with the Spec tyres, I run Captains tubless front and back at around 28/30psi on standard rims and the only time I've had a problem is when I cut the back tyre up running over broken glass.
Topeak Smart Gauge D2.
Reads in PSI, KG/cm^2 and bar
Tare function
swiveling head so you can always see the display while checking pressure
Switch to select Presta or Schraeder
Tune function too.
It was pretty inexpensive, and I tagged it onto an on-line order.
http://www.wiggle.co.uk/topeak-smarthead-digital...
Thanx Slowpup - was one of the two I had on shortlist - so now ordered
.
I have the same guage and I just don't trust it. If I inflate to the guage there's a lot more pressure then I was running using my (now broken) track pump. 30 psi seems rock hard and loses a lot of compliance. I can't cross-check it on the presta valve end but maybe I'll check it against the servo (hardly accurate itself) on the schraeder setting and see.
@ Dan. I trust the gauge to give me a repeatable result. Whether that means the number I get is exact, or an approximation, I'm not sure.....
I suppose that experimenting with pressures is what we all do to some extent, and maintaining the correct pressure once found is what we seek to achieve.
I like being able to say I ride on 17 pounds with my 81 kg lardarse too......
17 pounds? Yes.. but don't you have you have like 18 inch wide tyres on that thing (its a thing of beauty) of yours?
I run 25-30ish tubeless.. well actually I don't use a gauge anymore.. I just pump it up and squeeze the tyre, then sit on the bike, push the front end around a bit and and look at the deformation.. looks about right and go for a ride.
I currently use RR snakeskin on Stans rims and like them a lot, the TL one was a real PITA and I lost count of the times I had to stop and put air into it, by the time the sidewall actually finally sealed the stupid thing was near the end of its service life.
At 25-30psi I find that they never ever burp.
but on a P35 29er rim, so yes it does have a big contact patch....
not enough to save the rim when I landed on the corner of the sandstone block... though the RaRa still didn't fail.
+1 on getting Schwalbe TL sidewalls to seal up... I have one that is 2 years old and still leaks over 10 days.
Or you can try one of these: http://www.chainreactioncycles.com/Models.aspx?M...
I've had one for a few years and it's been reliable and extremely useful. So light it lives in my Camelbak.
I run a specialized Purg tyre on the front and a ground control on the rear. "2bliss" ready as Specialized labels it. Using stans on the stock Roval rims and no rim tape they have been run no lower than 30psi and up to 50psi and have had no troubles. Very thin compound I thought but I am a noob on the MTB seen, mho is they are useless with tubes and no sealant. ( Copped three punctures riding to work from thorns )so I went tubeless and now loving it!