DEAR UNCLE AL: I’m curious about “slime”-filled inner tubes. Is there a big downside to using them in a thorny environment like New Mexico? — Raphiel B.
UNCLE AL FIRES BACK: Sure, Raphie, go ahead and use a sealant in your tubes if thorn flats plague you. My favorite is True Goo, made in my state of Colorado. It works quicker than gel-like sealants, and it’s not much of a weight liability. Standing by the side of the road with a flat 60-gram tube, now that’s a liability.
Valve Stem Failures
DEAR UNCLE AL: A friend has had several flats lately. The strange part is the valve stem is pulling loose from the inner tube. Last night my son’s bike had the same problem. Now my curiosity is up. Is this caused by tightening the stem nut too tight? Or having it too loose? — Hal R.
UNCLE AL FIRES BACK: Try an experiment for me, Hal — don’t use the stem nut at all. I think that’ll solve the problem. Also make sure the tube and the inside of the tire are well coated with tire talc.
I prefer tubes that have smooth stems so there is no issue with stem nuts, which get misused. By tightening down the nut before inflation, your friend is preventing the tube from centering itself in the tire as air pressure is applied. This pulls the tube away from the valve and can (and does) tear it.
If your pal insists on using the nut, tell him to barely snug it after the tire is fully inflated, so it doesn’t rattle. Better yet, make a necklace out of ’em.
FEEDBACK FROM GREG K.: In my opinion, part of the problem with valve stem failures seems to be a combination of too little rubber at the base of the stem and too large of a valve stem hole in the rim. After many pressure cycles, the rubber fatigues and fails.
In particular, Mavic Open Pro rims seem to have a very large hole on the rim’s inner wall, which results in little support of the stem and more stem failures than some other rims I’ve owned.
A simple solution is an extra layer of rim strip (the good fabric type) with a small hole for the stem. If one doesn’t have a small hole punch, a Xacto knife (or any sharp knife) can be used to cut a small “X” in the center of the rim strip and allow the stem to pass through. Push the wings from the cut into the hole for more stem support.
FEEDBACK FROM JIM M.: I had several problems with valve stems pulling off. Mostly with my Ksyrium wheels. They do not use a rim strip, and due to the size of the valve hole in the rim, nearly all tubes will tend to be pushed into the hole by the pressure.
I finally cut a short piece of rim tape (about 2 inches long ) made a small round hole in it at the middle, and put it over the valve hole in the rim. This may make it a little more difficult to install a tube, but the tube lasts. No more problems.
FEEDBACK FROM LARRY S.: I ride 700x23C, 49-gram threaded-stem tubes in my Ksyriums. I only use the stem nut when I’m putting air in the tube, to prevent twisting/bending the stem when I dislodge my hard-to-remove air chuck. I have never had a stem failure, but I did when I rode 70g-75g, threadless-stem Michelin and Torelli tubes.
FEEDBACK FROM GREG S.: What I do is thread the nut all way down the valve stem and install the tube like that. What this does is put the stem a little lower in the tire so it doesn’t get tugged when pumpingthe tube. At 100 psi, the nut also prevents the stem from being pressed into the rim hole at the point it’s bonded to the tube.
Nuts on Valve Stems
DEAR UNCLE AL: On tubes with presta valves, exactly what is the purpose of the knurled nut that tightens against the rim? Is there any reason I can’t leave it off? The extra rotational weight adds up. Is there a different answer for clinchers than for tubulars? I guess that’s three questions, sorry! — Gary M.
UNCLE AL FIRES BACK: The nut is to hold the valve in place when you put the pump head on. I hate this type of stem. The threading makes the pump head hard to remove and it quickly wears out the rubber gasket.
Tubular tires (sewups) do not have threaded stems, as they are glued in place, or at least they should be.
Buy tubes with smooth stems, such as Michelin or Salsa. They work fine and won’t get pushed into the rim unless you’re a moron. My guess is that you’re far from it because you can count to three and know the importance of rotational weight.
FEEDBACK FROM SCOTT S.: Uncle Al, don’t forget that the nut stops the valve stem from moving side to side when pumping with the minimalist frame pump most people carry on rides. This prevents the valve-to-tube seal from rupturing, which can’t be repaired.
The nut also stops the valve stem from clicking against the rim when the wheel is turning. Nothing is more annoying on a bike ride than a repetitious noise. I’ve alleviated that problem on my track bike, which has threadless valve stems, with some Teflon tape. Of course, the tape probably weighs a few grams, but I’ve overcome that obstacle with my gargantuan thighs.
Obsessions with lightness over common sense and sound training is a little bit ridiculous. If riders simply cleaned the dirt and dust off of their wheels they would make up for the extra few grams for a stem nut.
Those are my two bits — a Canadian two bits I might add, which may be worth even less to a mechanic with an attitude, but you have them anyway!
DEAR UNCLE AL: Is there a suitable substitute for patch cement that comes in tube repair kits? Is like-smelling rubber cement the same thing? I seem to end up with useable patches long after those little tubes of glue have dried up. — Jim P.
UNCLE AL FIRES BACK: Stick with the glue formulated for your patches, Jimbo. I’m sure there is some other stuff out there that will work, but I’m too paranoid to try to experiment. Everything might be fine till it dissolves the tube.
Rema sells just tubes of glue for its patches. The stuff does dry out, so I’d suggest buying the smallest tube your shop can get for you. It’ll be only a couple of bucks and we all know, it works.
(We got a reader tip on this issue: After using glue, squeeze the tube from the bottom to force all the air out before snugging on the cap. This way, the glue won’t dry.)
Tube Patch Failures
DEAR UNCLE AL: Whenever I get a flat on my hybrid bike, I’m able to patch the tube with no problem. But when I flat on my road bike with its thinner tubes, I cannot get the patch to work. It usually doesn’t seal on one side. What secret am I missing? — Ka N.
UNCLE AL FIRES BACK: There shouldn’t be any real difference, Ka, whether you’re patching thick or thin tubes. So here are four tips that might help.
- Use a Rema patch kit, the best on the market.
- Make sure the tube is fully deflated before you patch it.
- Go very light with the sandpaper, then wipe the spot you’re patching to be sure it’s free of rubber dust and tire talc.
- Use tubes that are as close as possible to the size of the tire. A 700x18C tube will work in a 23C or 25C tire, for example. But a patch is more likely to pull away because it can’t stretch as much as the tube has to.
Routine Tube Replacement
DEAR UNCLE AL: At what point should I change the inner tubes on my road bike? One of the guys in my club swears by replacing his tubes every 2,000 miles whether they need it or not. What do you think? — Kathleen J.
UNCLE AL FIRES BACK: I’m not sure what’s magic about 2,000 miles, Kat. My rule is to change a tube when it has more than a couple of patches, when it looks old and scuffed during tire replacement, or if it’s a real cheap tube bought in a pinch.
If tubes are left forever in a tire or used multiple times when changing tires, they dry out, crack and lose their resilience. They become more flat prone.
If you buy good tubes made by Kenda, Michelin, Continental, Salsa, IRC and probably a few others I can’t think of at the moment, you’ll have better luck than with the cheapies.
Just remember a tube is not sacred. Don’t look at a tube or tire change as an ordeal, but simply homage to the bike gods, especially that little rotten one that gives us flats when we’re tired, irritable, hungry, at wit’s end — and still miles from home.
Lightweight Inner Tubes
DEAR UNCLE AL: I’ve been looking at some lightweight inner tubes that are made from butyl and weigh 49 grams. They could cut nearly 140 grams of rotating weight. Do they flat more easily? Lose pressure quickly? — Rick L.
UNCLE AL FIRES BACK: Yes and yes, Ricky. Personally, I prefer Michelin latex tubes, which are a bit heavier but don’t puncture easily. They lose pressure overnight so you need to pump them before every ride, but they truly enhance tire performance.