Jim’s Tech Talk
By Jim Langley
As the designated mechanic for our couples group who bike together some weekends, I run into interesting issues. Like last week, when Marc disappeared off the back and I went looking for him. He was a half mile behind standing on the shoulder trying to pump up the tubeless rear tire on his Santa Cruz.
He told me it wasn’t flat, only soft enough that he wanted to add a little air. The problem holding him up was that he couldn’t get any air into the tire with his pump.
We both checked his mini-pump by holding our hand over the head and making sure pumping created pressure. No problem there. We next made sure the tip of the Presta valve was unscrewed and the seal was open. The pressure inside the tire keeps the valve sealed until you break the seal by unscrewed and depressing the tip.
The valve seemed to be in working order, because pressing down on the tip as described produced the rush of escaping air. Since I had a pump, too, we gave it a try thinking maybe something was awry with Marc’s. No dice. My pump was useless, too.
Why couldn’t we get any air into the tire with the pumps? It was a bit of a mystery so I’m explaining what we figured out in case you ever have the same problem. And to help ensure you’re prepared to deal with related tire troubles, I’ll give some examples of other tire valve issues. They’re all relatively easy to fix as long as you carry the few small parts and tools mentioned.
When Marc’s valve allowed air out but not in, I asked Marc if he happened to have a spare valve core. Tubeless valves usually have replaceable cores. The core is the working mechanism inside the valve that keeps the air in and allows inflating and deflating.
Not all valves have replaceable cores. Especially in the case of valves on tubes. You can tell by looking closely at the sides of the top of the valve just below the knurled tip you screw to open/close the valve. On valves with replaceable cores, there will be two wrench flats on the sides.
There are little valve-core removal tools you can buy, such as Park Tool’s VC-1. You can also use pliers or a tiny adjustable wrench to remove them. The cores are tightened enough that you can’t get them out by hand.
Carry a Spare Valve Core
I recommend always carrying a spare tube to fit your bike – even if you have tubeless tires. And, I would also always make sure that tube has a replaceable valve core. All Presta valves with replaceable cores use a universal fitting Presta valve core. So, as long as you have a core with you on the spare tube, you will have a backup if you need it. You can also purchase Presta valve cores separately.
With Marc’s bike, he was actually carrying 2 spare valve cores in his seat bag, one for his bike and one for Sue, his wife’s Santa Cruz (attaboy, Marc!). So, we simply removed the valve core from his valve and screwed in a new one with Marc’s tool. After that, it was a cinch to pump up the tire and get rolling again.
We couldn’t tell looking at Marc’s old valve core what had made it refuse to accept air. And, I don’t know if we could have fixed it if we had time to soak it in solvent or blow it out back in my shop with compressed air.
But, it’s possible that some sealant from his tubeless tire made its way to the valve, got into the end of the core and gummed it up in a way it would let air out but not in.
Tip: To prevent sealant gumming up valves, it’s best to be sure to rotate valves to near 12 o’clock before deflating or inflating sealant filled tires. That helps keep the sealant pooled in the bottom of the tire and with luck it’ll stay down there.
Dealing with Sealant Plugs
Something that happens with sealant over time is it drying and forming a skin or plug. Since the tubeless valve is protruding inside the tire, it’s a natural place for the sealant to collect, dry and create a plug or a clog.
In that event, if you try to let air out, only a small bit will escape before the air flow stops. And your pump will be useless just like ours were with Marc’s tubeless tire.
The replaceable-core valve comes in super handy when you run into this problem. What’s needed to get the valve working again is pushing out or breaking through the sealant skin, plug or clog.
To do this, rotate the valve towards 12 o’clock and remove the valve core with whatever tool you’re carrying (careful; it’s small – don’t drop and lose it!). Once the core is removed, all that’s needed to clear the plug is to poke something inside the valve far enough to push out or poke through the sealant.
You don’t want to risk puncturing the tire, so don’t use anything too sharp. I like to use a 2.5mm allen wrench. It only needs to be long enough to reach through and into the tire. You could make a tool out of almost anything that fits through the valve.
Tip: It’s possible to poke something too small or too pointed into the valve plug and then still have trouble getting air in. That’s because it made too small a hole in the plug and the air sealed it again. If that happens, poke something larger into the valve to enlarge the hole.
Don’t Break the Bead Seal
In most cases, if you’re careful and work as described, you should be able to inflate the tire again and finish a ride after replacing a bad valve core or poking open a sealant plug. But, with all tubeless tires with sealant, you want to try to avoid breaking loose the beads of the tire from the rim.
When properly installed, tires are what’s called “seated” on the rim. This means that the edges of the tire on both sides and all around the rim are in the perfect position to seal any air from escaping. Since you are only working on the valve and not the tire, it will stay seated like this unless you make the mistake of trying to remove the tire.
And, as long as the tire remains seated, you should be able to inflate it and have it hold air – even if the sealant inside has dried up inside and there isn’t much left in a liquid state to help seal the tire.
If you mistakenly unseat the tire bead(s) on tubeless tires you may have trouble getting it to hold air again if there isn’t sufficient wet sealant inside remaining to help seal the tire. If you run into this situation, you need to add sealant if possible.
Ride total: 9,247
Jim Langley is RBR’s Technical Editor. A pro mechanic & cycling writer for more than 40 years, he’s the author of Your Home Bicycle Workshop in the RBR eBookstore. Tune in to Jim’s popular YouTube channel for wheel building & bike repair how-to’s. Jim’s also known for his cycling streak that ended in February 2022 with a total of 10,269 consecutive daily rides (28 years, 1 month and 11 days of never missing a ride). Click to read Jim’s full bio.