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Discussion Starter · #1 ·
I am setting up a pair of DT XR331 and Schwalbe Thunderburt with DT rim tapes. This is the 1st time I am doing tubeless.

I seated the beads on the rear first and pumped it up without any sealant. it took about 12h to get to 15 psi from 30psi. Is this OK?

But I am having trouble with the front (still no sealant yet). After I pumped it up, the pressure dropped quickly and was almost gone in 2 hrs. I can hear a very slight hiss from the valve, which is hand-tightened hard. it probably came from a small slit on the tape at the valve hole.

There's a few things I don't quite understand. Why does the valve hole have to be covered with tape and then cut open? I thought the rubber grommet on the valve will seal well against the aluminum edge of the rim hole if it is clean and flush. With the tape, if it folds and is creased at the hole, doesn't it make the rubber grommet harder to fully cover the hole edge?

And how well should this set holding air without sealant? I've heard quite some combos hold air very long w/o sealant.

Or maybe I should get better valves? Are valves with the U-shaped grommet better than conical grommets?

Thanks!
 

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Norðwegr
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Just use some sealant and none of this will be an issue.
Pinholes in the sidewalls of tires and the mentioned valvehole will leak unless sealant is added. The latter will sometimes seal without, but that's a lottery.

If you're concerned about weight you can use sealant for a couple of rides so it fills in any leaks and remove any that's still liquid. Personally I'd leave it in, whatever weight saved you can remove with a bathroom break.
 

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damned rocks...
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Even if it leaks at the valve hole it doesn't mean it's leaking at the rim/valve interface, depending on your tape setup it could be leaking at any of the nipple holes.
The valve hole it's just the place the air can escape more easily.
 

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A tire can slowly seep without sealant, but sealant is not a must for tubeless. Sealant is there in the event of a puncture, and to coat the tires pores.

If it is leaking from the stem there is a problem someplace. Good to sort those things out before adding sealant actually.

I suggest breaking down the tire and inspecting your tape. Look for an area that doesn't look well adhered.

Or maybe your stem isn't in tight enough. NO tools. Finger tight only, just make sure to push down hard with your thumb from the inside and tighten the nut.
 

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Sounds like you are 90% there...leaks you mention would easily be sealed when you add sealant. Check out Stan's website for some videos on using sealant. Get a squirt bottle and fill w/soapy water to check for leaks. Much easier to find than waiting and checking pressure then wondering where it's leaking from. Just verify no leaks and go ride.
 

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Just to reiterate some points.

If you hear air coming out at valve, recheck the tape job and how well the valve is seated. It could be either allowing air through.

Pin holes will be filled by sealant. Faulty taping won't - if sealant gets under the tape, it will hinder the adhesion. A poorly seated valve will eventually, but it's better to fix that rather than relying on sealant.

I find that an aired up tire (like when I air up a Maxxis at max pressure to stretch it) will hold air for a week without losing more than a few PSI, even without sealant.
 

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Discussion Starter · #9 ·
Just use some sealant and none of this will be an issue.
Pinholes in the sidewalls of tires and the mentioned valvehole will leak unless sealant is added. The latter will sometimes seal without, but that's a lottery.

If you're concerned about weight you can use sealant for a couple of rides so it fills in any leaks and remove any that's still liquid. Personally I'd leave it in, whatever weight saved you can remove with a bathroom break.
Thank you. I am not so worried about weight. Just wanted to make to as good as possible before the sealant comes in.
 

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Discussion Starter · #11 ·
A tire can slowly seep without sealant, but sealant is not a must for tubeless. Sealant is there in the event of a puncture, and to coat the tires pores.

If it is leaking from the stem there is a problem someplace. Good to sort those things out before adding sealant actually.

I suggest breaking down the tire and inspecting your tape. Look for an area that doesn't look well adhered.

Or maybe your stem isn't in tight enough. NO tools. Finger tight only, just make sure to push down hard with your thumb from the inside and tighten the nut.
Yeah I'll ride with sealant in but wanna make sure I don't make mistakes that even sealant can't save.

The major leak should be from the valve stem cuz I can clearly hear the hiss there. It can be louder if I move the stem around but won't get any smaller. I hand tightened it pretty hard with the push, and now when I took it part the rubber clearly got a cut on it probably from the edge of the hole. I am not sure if this makes it worse.
 

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Discussion Starter · #12 ·
Sounds like you are 90% there...leaks you mention would easily be sealed when you add sealant. Check out Stan's website for some videos on using sealant. Get a squirt bottle and fill w/soapy water to check for leaks. Much easier to find than waiting and checking pressure then wondering where it's leaking from. Just verify no leaks and go ride.
Yeah if i can't make it perfectly sealed w/o sealant, I'll just put sealant in and it's supposed be used with it anyway.
Interestingly I did use soapy water to rub the whole beads and the valve stem and there was no trace of leak. But clearly the valve is leaking because I can hear it. Perhaps it is leaking at the inner layer and air gets in b/w two layers and gets out from the nipples holes.
 

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Had this with some tubeless road wheels. Lbs put in a bit more sealant and with the valve to the ground bounced it like a basketball. Sealed in seconds and never leaked
 

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Discussion Starter · #14 ·
Just to reiterate some points.

If you hear air coming out at valve, recheck the tape job and how well the valve is seated. It could be either allowing air through.

Pin holes will be filled by sealant. Faulty taping won't - if sealant gets under the tape, it will hinder the adhesion. A poorly seated valve will eventually, but it's better to fix that rather than relying on sealant.

I find that an aired up tire (like when I air up a Maxxis at max pressure to stretch it) will hold air for a week without losing more than a few PSI, even without sealant.
Holding air for weeks, that's what I want but probably won't be lucky enough to get with my setups.
I think it is the small cut in the tape around the hole that's causing the leak, and the tape on other places seems fine. Can I just cut the section few inches away from the valve hole and retape only this part? Or i have to retape the whole rim.
 

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Holding air for weeks, that's what I want but probably won't be lucky enough to get with my setups.
I think it is the small cut in the tape around the hole that's causing the leak, and the tape on other places seems fine. Can I just cut the section few inches away from the valve hole and retape only this part? Or i have to retape the whole rim.
Won't hurt to try it. Or put another layer on first. Or you can try a different (Stans Vs. DT Swiss) valve.
 

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In case it wasn't understood- we aren't suggesting to fix tape at the valve. We are suggesting that the tape itself isn't properly adhered, or applied and air is seeping behind tape and finding the area of least resistance -the valve hole under the tape with is under the valve stem.

However, the valve stem itself could not be sealing properly. It's sort of common for a Specialized valve stem not to seal properly.

If it is flat in 2 hours, there is an issue. Your tires should hold air for 2 hours without sealant. As long as they are tubeless tires.
 

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No, I wouldn't expect it to hold air for 2 weeks without sealant. It's a system, and the sealant is part of that system. It fills in all the tiny gaps and pinholes. Put the sealant in it and rotate it/flip it/swirl it for a day, and then see how well it's holding air. I would expect my tires to be pretty close to flat after 2 weeks, with sealant (maybe they wouldn't be flat, but I'd be more surprised if they held anything close to full pressure).

My first try I did some combination of overtightening the nut on the valve stem and cutting the "x" slit in the tape too wide and using Stans valves. I was cutting "x" from metal to metal, which was leaving a gap. I corrected it by just making the "x" half the diameter of the hole and letting the valve stem determine the size it wanted the hole...been working fine for several years this way.

And, just because the air is coming out at the valve hole doesn't mean that is where the air is getting through the inner wall (tape). Your rim (presumably) has a double wall with holes through both walls at each spoke, too, and when the nipple is filling the outer holes and the tape is covering inner holes the air could go through a spoke hole and find it's way to the valve hole.
 

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Yeah if i can't make it perfectly sealed w/o sealant, I'll just put sealant in and it's supposed be used with it anyway.
Interestingly I did use soapy water to rub the whole beads and the valve stem and there was no trace of leak. But clearly the valve is leaking because I can hear it. Perhaps it is leaking at the inner layer and air gets in b/w two layers and gets out from the nipples holes.
If you can hear air coming out that's a good sized leak...surprising you can't find it with soapy water. It's best to confirm source of leakage so you know what to fix. Sometimes it's simply the interface between valve stem and rim and taping isn't the answer. I would take wheel off bike, fill tub and check it that way. You could be chasing your tail spending time re-taping only to find that was not the fix.

I have had valve stem/rim issues before and even though I can get sealant to stop the leaks. The problem is, whenever you add air you are disturbing that interface and it can re-emerge. Usually bouncing wheel around will reseal but it's best to solve it once and for all.

Inspect the hole drilled in rim from ID side, check for burrs, get it to a clean smooth surface all the way around to ensure a good seal. Verify the tapered rubber seal interface of the stem is in good shape too. Some stem designs are better than others.
 
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