Fun with Tubeless Tires

Tubeless bike tires are an innovation in cycling that started in mountain biking and has percolated towards higher-pressure road tires. Right now, most road cyclists still use a traditional inner tube to hold in the air inside the tire that provides structure and tread. Myself, I mostly use tubes, but when I needed to replace my Roubaix’s tires before the Badlands Gran Fondo, I elected to try tubeless again. Tubeless promises:

  • Fewer flats since the sealant inside will fill small punctures,
  • Eliminating “pinch flats” caused by hitting a sharp edge and pinching the inner tube, and
  • Being able to run at lower pressures which is more comfortable on the road.

The start of the 2021 season was full of punctures for me. I think I had 5 or 6 over the first month of the season. And it was even worse, thanks to the bike parts shortage from COVID. I found myself patching tubes instead of replacing them. But since late July, I’ve been riding a set of Specialized 2Bliss tires and I’ve not had any punctures.

That’s the good part. The bad part is that my tires have been going flat overnight. They leak enough air slowly that they go softer over the course of a ride and are down to about 10 PSI in the morning. It seemed like it was getting worse, too. I went for a 4-hour ride to Bragg Creek yesterday. I started at 95 PSI and ended at 50 PSI. With the Tour de Victoria coming up, I am worried that my tires might be effectively flat before I finish the ride.

I am in the middle of trying to solve the problem right now. The short version: I don’t think I added enough sealant to my tires the first time around, and the sealant dries out over time (making the problem worse, as observed). I’m embarrassed to admit it, but I only put 20 mL of sealant in each tire originally. I added 20 mL more last night, inflated to 80 PSI and then left them for 2 hours. After 2 hours, they were down to 40 PSI. 😭 I did some research and I did a “bubble-test” in the bathtub this morning. To my surprise, it looked like the bubbles were forming on the sidewalls. I expected them along the bead or maybe at the spokes or valve. A little more research found that some tubeless tires have a thin sidewall and air can escape. The solution: more sealant, applied properly.

I have added 40 mL more to each tire and made sure to coat the insides well. In an hour and a half, we’ll see if I was successful. 🤞


I think that was successful. I’m doing a longer test now, but the pressure in the tires was much higher after 2 hours than it was previously. My way to measure isn’t very accurate, but I think it was only a drop from 80 to 70 PSI. I’m doing a five-hour test now.