chrisusmc

Hello,
I have a Public Bike, V7. The tubes in the rear, wear out within a couple of days time. Its always in the same spot, on the place where the nipple meets the tube. I've take it to a mechanic and neither one of us can find any reason why this should be. There doesn't seem to be any noticeable deffect. Has anyone seen this before? what can I do to fix it?
Christopher Williams

Unca_Sam

What pressure are you using in the tires? What's the pressure range on the side wall?

CliffordK

Are you riding the bike after the tire starts going soft?

What angle is the valve when you stop to repair the flat?

My thought is that you could have something else wrong, like a radial tire wire that gives you a slow leak.

Then, as the tire starts going flat, you start getting slippage of the tire, and tear the valve.

Andrew R Stewart 

"nipple meets the tube"

To me this suggests that the spoke nipples are somehow abrading the tube. Rim strips are meant to cover nipple ends (and any access hole for said nipple to be inserted) so tubes are protected. Is there a rim strip present? Andy

WizardOfBoz

Andy, I think that chrisusmc is referring to the valve stem when he writes "nipple", not the spoke nipple. And I'm always 100% correct and spot-on, except on days with names containing "y". (That is, I could be wrong -- Chris, where exactly are your leaks appearing? Valve stem, or spoke nipple?)

chrisusmc, if you are indeed referring to a leak at a spoke nipple (the metal things that screw onto the end of each spoke), then Andrew nailed it: there should be a rubber strip running around the inside of the rim, covering those nipples.

If the leak is persistently at the air inflation stem, and you do have a rim strip, then I would check the edge of the air stem hole in the rim for sharp edges, or for being too tight or loose or you have a tube/rim mismatch.

As to mismatch: A brief check of pictures of this bike show that it uses Schrader valves (that is, air valves like in a car tire). There are also tubes that use Presta valves (smaller diameter, with a little valve nut that you loosen to allow inflation/deflation, or tighten to seal). If your bike has wheels with holes drilled for Schrader valve stems and you are using tubes with Presta valves, that could be an issue. The hole would be too big for the valve stem in your tubes. Use Schrader valve tubes, or if you must use Presta, get a Schrader to Prester adapter bushing for each wheel:

https://www.amazon.com/Schrader-Presta-Rubber-Rim-Hole-Adaptor/dp/B000XNZU1S?SubscriptionId=AKIAILSHYYTFIVPWUY6Q&tag=duckduckgo-ffab-20&linkCode=xm2&camp=2025&creative=165953&creativeASIN=B000XNZU1S

pdlamb

You might take a chamfer or some (rough) sandpaper and smooth the valve hole down on the rim.

If it's on the outside of the wheel (contacting the tire), look for a small cut in the tire. Sometimes the tire can "chew" up the tube until it develops a leak, usually in 3-4 days IME.

J.Higgins 

I did a quick google search, but could not verify my suspicions that Public Bikes are made in China, which would further validate your idea about the sharp edge on the valve stem hole. I bought a Linus (Chinese-made) mixte for my wife, and it was a real mess when I got it. Right out of the box, everything was crooked, sharp-edged and out of true. I'm pretty anal about bike assembly, so the whole bike was stripped and re-greased and the wheels trued and spokes tensioned. So far its been a decent bike for her, and good looking as well. Anyway, I suspect that you are correct in assuming that this may be the root cause of the OP's dilemma.

WizardOfBoz

We've been ghosted, fellas!