Mystery flats near the valve? Maybe not so mysterious!

Those two bulging spots near the valve? They are *not* weak spots in the tube! Or at least they weren't weak/defective when installed. Read on.
Those two bulging spots near the valve? They are *not* weak spots in the tube! Or at least they weren’t weak/defective when installed. Read on.

Another “mystery flat” in the shop¬†today, one that had previously seen three unexplained tube failures, but today that would end. You see, I’ve been down this road before, a road that goes like this- a tube, no matter how thin or defective in one section, cannot be forced to bulge because it’s held in place by the tire. Anything you see that looks like a bulge or rupture usually represents some external force in play.

This particular tube was leaking at one of those bulges. No surprise there; they look scary and the rubber has thinned out. But how? Nothing funny about the rim or tire.

Closeup, showing the lines to the right of the valve, where the tube has developed leaks from being stretched too thin.
Closeup, showing the lines to the right of the valve, where the tube has developed leaks from being stretched too thin.

Here’s how it happened. During inflation, the person pumping up the tube is pushing the tube’s valve up into the tire, creating a cavity underneath. As the pressure increases, the tube fills in underneath, bulging downward into that cavity. That’s how you get those funny spots either side of the valve. Over time, sometimes not too much time, that thinned-out tube fails. In the smaller photo, you can see what look like small cuts; those are the areas the tube has split and now leaks.

What to do? Make sure you’re not pushing the valve up into the tire as you pump! Especially if you’re inflating a tube that already has a fair amount of air in it, since pushing it upward under those conditions pretty much guarantees the tube is going to try and bulge in to fill the empty space. ¬†–Mike–

Print Friendly

Great reverse-Pescadero w/West Alpine ride!

Peacocks on Stage Road, Flanders flag on West Alpine and a spooky tree
Peacocks on Stage Road, Flanders flag on West Alpine and a spooky tree

I was a bit apprehensive about today’s ride, having missed Thursday morning’s ride while in DC, and in fact I didn’t have anything close to what it takes to keep up with Kevin on Old LaHonda, as he posted an 18-something, about three minutes faster than I could pull off the climb. But I actually felt pretty good, maybe because it was a bit warmer and my lungs definitely prefer warm to cold.

The run to the coast seemed faster than it was; it really seemed like we’d have a Strava PR, but nope, despite burying ourselves into the slight headwind, it was hard, just not as fast as it felt like. Lunch in Pescadero was the usual awesome, but Haskins was the first sign that our legs had limits, Kevin’s in particular. And then West Alpine. As beautiful as ever, but we had to take it pretty easy, plus two stops on the way up, first to shoo a snake out of the road (remember, we stop for snakes), and the second to get the picture of the Flanders flag someone’s flying from a tree on West Alpine.

I mentioned it was warm? Saw just over 80 on West Alpine, cooling off to the mid-70s on Skyline. 68 miles total, and I’ve felt all 68 of them. Which is, of course, a good thing.

Print Friendly