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  1. #1
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    Thorn Resistant QTubes breaking

    With nine of us all mountain biking and racing (yes, I have a wife and seven mountain-biking children), I am tired of changing blackberry-thorn- and goathead-induced flats on my regular Kenda QTubes and thought back to the time a few years back when I put in a super-thick tube that lasted about three years until the stem finally broke off (although I cannot recall the manufacturer now).

    I understand many of you will recommend that I simply go tubeless, and that may happen some day, but I just don't have the time to convert all 12 or 13 of our mountain bikes--everyone has one, plus two shared single-speeds and a loaner or two. That would be somewhere around 25 rims to replace or adapt for tubeless, to say nothing of changing the fluid periodically.

    Despite tubeless being a great idea for a solo, pair, or even a trio, the thought of all that work is more than a bit daunting for me, so I resume the real story, where I happily trotted off to my favorite bicycle supply shop and purchased a pair of QTubes thorn resistant tubes for each of us--for just about twice the prices of a regular tube.

    "Well", says I, "Double the price for five times the life is a good deal."

    That turned out to be a nice thought while it lasted. In reality, in the last six weeks, two 29er tubes have split down the inside seam, and my 85-pound 13-year-old-son has had the valve stems break out of two 26" tubes. None of these failures was associated with a jump, hard turn, or any other particular heavy turning, braking, or other tube trauma.

    The bike shop is perfectly willing to warranty these out; however, I do not know if I want to continue down this path. My 13-year-old is afraid to have these tubes in his tires for his 100-mile MTB race in two weeks. He would rather risk a thorn than a broken valve/tire joint. Of course, we can pre-slime the tubes, and probably will, but it still leaves this question:

    Is it just me, or has anyone else had issues with these particular Kenda QTubes? It seems to me that four catastrophic failures within six week indicates either a bad batch (not likely, given that there are both 26 & 29 involved here), poor design, poor quality control, something we are doing incorrectly (other than riding every day), or maybe just bad weight/pressure combinations. My tires have not yet failed, but then I weight about 185, so I could surmise that they a problem only with lighter riders. Possible? Ideas?
    Last edited by Brain; 07-09-2013 at 05:38 PM. Reason: Modify wording

  2. #2
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    I don't know about QTubes. Generally though, thick puncture resistant tubes and slime are heavy. I never use them, but I don't have any real problems with flats. Not enough to worry about anyway.

    My brother lives in an area with lots of the goat head thorns and he can't ride his commuter bike a single day without a flat. He didn't want to mess with tubeless either. What he ended up trying that worked very well was the tire liners that are a thick strip of fairly hard plastic that goes between the tube and the tire. He hasn't had a flat from a thorn since putting them in.

    These are the ones he used: Product Line
    I'm not very smart, but I can lift heavy things

  3. #3
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    I've gone to injecting my tubes with Stan's sealant before I install them. Stan's makes an injector syringe with a nozzle that screws onto both Schrader and Presta. It includes a tool for removing the Schrader valve but for Presta you either get special tubes with removable valves or unscrew the little nubby on the end with pliers. You might want to practice that on a few old dead tubes first.

    Although I haven't had any actual 'near flat experiences' yet, I did intentionally poke a hole in a tire and it sealed up in a few seconds and has held air fine since.

    Stan's will dry out over time, but in a tube the air loss is usually less than with a lot of tubeless setups, so the rate of dry out should be pretty slow - maybe six months. I calculated the cost at one point, but its was cheap enough to be irrelevant - maybe $1.50 a shot - compared to dealing with flats and patches.

    Valve stems breaking out can be due to a lot of factors, but the tire slipping on the rim and pulling the tube around, along with burrs and such at the valve hole, is the usual. I had no end of tire beads walking when I was running 26" and Kendas but since I went 29 I've used Schwalbe, Maxxis and Specialized and had no problem at all. I think a tubeless ready bead has a lot more rubber coating and a tighter fit which solves the problem. It's also maybe more of a problem with v brakes than discs.

    Regular Kenda tubes seem to be reasonable quality; I've never had a problem with them, but there are some rather crude off brand offerings at bargain prices that I'd avoid.

  4. #4
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    Yeah, I used the strips once or twice in the past also, and I think they worked relatively well, but they were a bit of a hassle just on my bike. With all of us riding, ages six to 51, tire sizes 24, 26, 650B, and 29, I was hoping for the simplest solution when I bought the thorn-resistant QTubes. It is not as though we get any more flats per person than anyone else, and we really do not ride in our nearest goathead country (eastern Oregon) all that often, so most of our flats are blackberry thorn pricks; however, statistically, with nine of us riding or racing most days, someone is simply going to flat much more often than one or two people riding twice a week.

    I was just trying to find out why we are having so many non-thorn-related problems with the thorn resistant QTubes. I know the thorn-resistant tube solves my thorn problem; I am just disappointed that they are failing catastrophically for other reasons.

  5. #5
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    Maybe time to try some different tubes ,maybe some preslimed tubes .Sounds like you are doing most of the repair work ,maybe its time to teach the kids how to do it themselfs.

  6. #6
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    I appreciate the input, and these are all options--just not the one I was working through today. Actually, the children are experienced riders and racers that carry all the tools, extra tubes, & master links and regularly help others repair chains and tubes on the trail.

    However, it still slows down the family or upsets a race when someone gets a flat, and as I indicated, this is a recent test for us in which I was just trying to minimize the number of flats to maximize our uptime on the trail, and my question has to do with why these particular tires are failing, not with how to resolve the underlying thorny problem.

    QTube is just one of many options, I understand. I already know about anti-flat strips, pre-slimed tires (with Slime or Stan's), and tubeless. I may, in fact, resort to just pre-sliming their tires in preparation for the High Cascades 100 in two weeks.

    I suppose I should have clarified: right now, I am asking the question only to see if this is a known issue with these specific Kenda thorn resistant QTubes or if there actually are riding style or rider weight issues affecting them before I call Kenda tomorrow to point out what I think is a fault in the design. I am really just trying to save myself the embarrassment of finding out something basic about tubes that I might not know when I call Kenda tomorrow.

    I was just going from my memory of my three years and ~6,000 miles without a flat when I had thick tubes, but they were not QTubes, and I evidently misjudged when I assumed all tubes were created equal. Or maybe we are doing something wrong with them.

    Also, I missed the fact that there is a wheels and tires forum here, so I am re-posting over there.

    Thanks again.

  7. #7
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    Over the years I have seen hundreds of broken valve stems on TR tubes of various brands, whereas I have only seen a handful of standard weight tubes with broken valve stems.

    bulerias hit on one of the reasons which is the tire sipping on the rim (during braking), this doesn't happen nearly as frequently with regular weight tubes because they expand easier and hold the tire tighter to the rim at lower pressures than thorn resistant tubes. Older tires which aren't as sticky and lower pressures contribute to this problem.

    Secondly, manufactures typically mark tubes to fit a range of tires from about 1.75 to 2.3 and most barely have enough volume to fill a 1.75 tire without stretching a lot. By the time they expand to fit a 2.2 they are really stretched, especially the area right around the valve core. You can see this if you inflate one to tire size without the tire.

    Broken valve stems is a problem with TR tubes, not a brand problem IMO.

  8. #8
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    I had the problem with the thorn-resistant stems breaking off all the time. The tube is so rigid that it moves back & forth within the tire and finally stresses the stem so that it gives out. I had to back to regular tubes and Stan's flatproof stuff that I got at Performance. It works better than Slime.
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  9. #9
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    bulerias: missed your post among the others the first time around. Good info. We have had no problem with regular-weight Kenda QTubes, so I think I will go back to those with Stan's. FYI: we are all on disc brakes, and it is the lightest rider (and thus riding with less tire pressure) that had the valves break off.

  10. #10
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    JB Weld & Finch Platte: thank you! This is the kind of detail I was looking for. I actually called Kenda about it this morning, and they admitted that poor vulcanization of the valve stem to the tube is not uncommon and will result in this problem.

    Interestingly, it is the lighter rider (85-pound 13-year-old) having the problem--but that may just be because he is a much more aggressive (euphemism for "skilled") rider than I am.

    I am definitely going back to our standard weight tubes with Stan's, although I will probably have to buy my Stan's by the gallon with nine riders and 12 mountain bikes at home!

  11. #11
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    There are receipes for making your own sealant somewhere here.

  12. #12
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    Search Best Tubeless Brew in the 29er Components section. Make it for less than 1/2 the cost of Stan's.

  13. #13
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    I've tried the TR tubes and they were god awful heavy, they felt like I added 5 pounds to the bike. The tuffy tire liners work ok but can be a pain to get positioned right and still add all that rotational weight. If tubeless is not an option many have success squirting stans in the tube. I've tried my own homebrew of tubeless sealant after reading the monster thread, it worked ok but I went back to stans. It's a little more $$ but worth it IMO.

  14. #14
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    I finally decided to just go with Stan's in the tubes for now. I have used other sealants on occasion in the past, but I have heard that Stan's is one of the best.

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