krb49

I have a Giant Cypress SX hybrid, Xero lite XSD-29 wheels, tubes w/presta valves, new rear tire, new liners, and new tuffy liners. My problem is continuous flats, I mean flats from the bike just sitting after new tube installation by the bike shop. I don't work on my bike at all. At least 9 new tubes in past 2 weeks, most are popping at the base of the presta valve stem, as if it's poor construction, 2 tubes have split at seam while being wheeled out of the bike shop. Nothing has been found in the tire, rims, or any holes in tubes except at the bad seams and at the base of the valve stem. Does anyone have any suggestions that might help me, I can't go on a ride without making sure someone is available to come and get me???? Appreciate any help at all. We have tried different tube mfgs, thorn tubes, and the liner installed was supposed to be the best, I can't recall the brand, would know it if I saw it again.

nepg

Maybe the LBS isn't using a friction-reducer like baby powder or corn starch...? Not sure what else, but someone else will have more/better suggestions.

mawtangent

You might want to think about getting more involved with fixing your own flats (as in dismounting your tire, inspecting things, patching the tube, and re-mounting the tube/tire, regularly using a good floor pump with a gauge, and maybe carrying a spare tube, patch kit and small frame-pump on your rides). That way you can begin to better diagnose your problem ("professionals" have their own biases and opinions which might steer their solutions in specific directions, but they often only see a snapshot of the situation, and no one is going to care more about your flats than you are, and that fact can motivate you to get more involved with finding a solution). Patching your tubes will save you money (though I admit will not be a help for stems broken at the base).

Many seem to get good results with liners, but I've heard that a tire liner can actually cause a flat by cutting into the tube (especially where the ends meet), if you get involve and investigate after every flat you might find evidence, or a pattern. For instance I once booted my tire with a ridged piece of plastic, I got a flat, and could clearly see the imprint of the shape of the boot in my tube, and it was clear that the boot had acted like a knife and pierced the tube over time. I knew I had to use softer materials for booting tires.

There are techniques for dealing with valves (and for me I find the presta-type especially fragile). If you are too rough, or you have to wrestle to get the pump head off you can tear them at the base (I've done this at least twice). The trick is to work with the valve in such a way as to never put undue stress on the valve (When I take the pump-head off I try to gently pull strait up instead of prying the head off in a side-to-side motion). From reading and searching on BF I learned that some models have pump-heads that are more "cooperative" than others. For portable frame pumps (that you attach to your bike) the ones with hoses get the best reviews (there is info on BF on how to use a frame pump (with no hose) without ripping out the stem). I'm still using a no-hose frame pump and I've got decent results. The trick for me seems to be holding on to the pump with the wheel/tire (off the bike) held up in the air and the stem pointing strait down, and letting the pump hold up the tire, and touching the wheel/tire a little as possible. Others use a technique where they use their hand to form a bond with the the wheel/tire as they pump. In both instance the goal is to put no undue stress on the valve stem.

Anyway, flats are just part of the experience, but don't give up, if you are riding on pretty normal surfaces (relatively free of goat heads, glass, etc.) you should be able to go several hundred miles between flats (some here go 1000+ miles without flats). For me just using a beefier tire on my back wheel cut down my flat by like 75%. You just have to be patient and "find your own way" through this rough period.

FBinNY 

You didn't say, but it might be the result of using large tires on narrow rims. If you look at a tire and rim in cross section, (I looked for a decent picture and couldn't find one, so if any poster finds one send me the link and I'll insert it here) the tire forms a large circle open at the bottom, with a small chamber within the rim below the narrowest point . When you start to inflate the tube, it fills the tire and stretches across the gap at the bottom. As you continue to inflate that narrow unsupported area balloons out to fill the lower chamber stretching it more than the rest of the tube.

Well made tubes handle it well, others get stretched so thin they are almost ready to burst before you ride. A valve with a base flange that's fairly wide sometimes gets hung up high in the tire so the tube right near the valve is especially stretched (good ones are reinforced here).

Starting with well made tubes of the right size helps - the largest, that's still smaller than the tire is best. Powdering the tube so it can slip within the tire and equalize the stretch also helps, as does making sure the valve's base flange can easily slip down past the pinch point. Lastly one extra step during installation, push the valve up into the tire, then pull it back down firmly to the rim before inflating.

BTW- none of this is new or rocket science, so if a shop mechanic can't reliably replace tubes so they won't burst in the belly, either the shop is selling poor quality tubes, or they have a poor quality mechanic. Neither bodes well as indicators of how more complex repairs would be handled.

krb49

The shop has been around probably 15 yrs or more and has always been real responsive to any problems. So far he hasn't charged beyond the initial repair for any of these tubes or liners. You mention the powder and that is one thing I don't remember seeing him do. I have watched most of these repairs being made. I think I understand about the "cross section" and can see where that extra stretch would come into play, but these are popping right at the base of the stem, as if the rubber isn't sealing tight to the stem base, and most times without being ridden. First thought was poor workmanship, but then after trying different brands of tubes we're back to base one. Should mention, the front tire is original.

10 Wheels

You have a problem that seems as only a hands on situation can correct.
FBinNY is the best for help here.
I have had 53 flats and know the cause of most of them.
Pics of the rim at the valve area might help? Pics of the tubes may help?

FBinNY 

If the bursting is consistently near the valve, focus on the valve area possibilities. Insufficient reinforcement at the base of the valve. Base flange too wide, and hanging up in the tire. Valve not pulled down and seated prior to full inflation.

The last two are critical, and failure to pull the valve down would cause exactly what you describe. The tube is inflated while the base of the valve is hung high in the tire. The air pressure forces the tube down into the hollow of the rim, and if the valve doesn't drop with it the tube tears away.


One trick that I use on my own tubes for a particular tire and rim which has given me similar headaches, is applying an oval feather edge patch with a hole punched in the middle as extra reinforcing at the base of the valve.

BTW- I don't know if someone asked or you mentioned; these rims are drilled for Presta and not Schrader are they not? If drilled for Schrader, a reducer bushing or washer at the base of the valve is required.

One other thing, my posts apply if the burst is near the valve, but recently I've seen tubes where the valve stem is shorter and there's a unsupported rubber section making up the distance from the end of the valve to the tube proper. If yours are like this, (you can feel it) try different tubes.

krb49

I think I understand about the "cross section" and I checked the tire replaced is the same size as the original that came on the bike. Tube size I'm not sure of, I'll try to check, but the shop has always done good work for me and I feel he knows what he's doing, just ran into something weird here. Thanks. (

FBinNY 

I admire and respect your patience and loyalty. I wish I could see your tire and rim or watch the mechanic do the installation, but without that it's hard to know how to help. One question, exactly what tire and rim are you using, or more important, how wide are they. The most important dimension is the inside width of the rim.

I understand that the shop is doing the best they can for you, but they seem to missing some detail which will seem obvious and simple in retrospect, but at the moment seems a mystery.

You might print this thread and bring it with you on the next visit, and maybe it'll help the mechanic spot what he's missed before.

krb49

I'll certainly print all of the responses out. Both for him and me. I really appreciate the efforts here. The tire is a Kenda 700x40c on the rear, same size but Michelin on front. I can't find any markings on the wheel other than the: Xero lite XSD-29. If I need to actually measure the inside of the rim, I won't be able to till Tue. when the shop is open again and they get started on this repair.

FBinNY 

I checked and the rim certainly seems wide enough that there shouldn't be serious issues. It's a large tire so make sure they're using a wide enough tube and not stretching a 700x23-25c to it's limit. With the right tube, and maybe the powder it shouldn't be a problem at all, so I'm stumped.

BTW- My city bikes in Mexico have 700x38 tires on on similar rims and never had a problem. I use 700x28-35 tubes.

frankenmike 

Hit the valve hole with a needle file to smooth the edge in case of micro-burrs. BTW, Mr. Tuffy liners can actually cause flats IME, ironically- might not be the case here but perhaps worth looking into at this point.

krb49

I'll try the file. Would the tuffly liners cause these kind of flats? All of these with the exception of 2 were right at the base of the stem, the other two were along seams in the tube where the seam actually split apart.

FBinNY 

Burrs at the valve hole might be a possibility, but I suspect with damage right at the valve the mechanic would have checked it. Certainly it won't do any harm to check and de-burr it. The long splits usually happen when the tube isn't well positioned and is trapped between the tire bead and rim, a mistake i doubt (hope) a pro wouldn't make.

All in all, I suspect that they're just using too narrow a tube for your tire, discretely check the box on the next visit.

krb49

I have meant to ask, but had forgotten. What do you think about drilling out the holes and using Shrader valves, from what I've read they are more heavily constructed???

FBinNY 

It won't solve the problem because it isn't the valve failing, it's the tube near the valve. Also if it's a rim width issue, which I don't think it is, a Schrader valve could actually be worse because it's even wider.

krb49

With the 700x40c tires what size tube should I be using? I've watched the guy at the BS and I want to say the last two #'s on the box of tubes he's been using is 38, but I'm not certain. If I have an idea Tuesday I can watch a lot closer. Really appreciate your interest and advice.

FBinNY 

Ideally you're looking for a tube in the 35-40mm width range. When he mounts the tire, watch at the very end and see if he finishes by gently pushing the valve up into the tire and pulls it back down. That serves two purposes. First it pulls any tube trapped under the tire's bead up into the tire, and pulling it back down endures that the belly of the tube is settled before inflation.

If he doesn't do that step, as soon as you get home, let the air out and do it yourself. If that doesn't do the trick it might be a tube quality issue, maybe the shop got a box of defective tubes.

krb49

With everything I've been given here, I feel like I can go in Tue. and at least have a basic understanding of what's going on and can ask some more appropriate questions about the procedure. Really appreciate the patience you all have displayed, will get back with results (hopefully in the positive). thanks again

krb49

Just returned from BS, tube is 700x35/40 thorn tube this time, the tech did "flex" the stem by pushing it in and out seating it on the rim. They're keeping the bike after they make the change and they say they're going to ride it to put it through the paces and see what happens. One thing he did this time is completely remove the little nut on the presta stem, saying to alleviate any possibility of that placing strain on the stem. They said the rim take they're using has such a small hole in it, it performs the same function as the oval feather patch would, velocity tape. I'm in a wait and see what happens situation for now. Thanks.