Tech Tuesday

Q: I am using Enve SES 3.4 AR wheels mounted with Vittoria Corsa Control tubeless-ready Graphene 2.0 tires. For some time I did not use an inner tube, just sealant. Nevertheless, every other day I had to inflate them. I decided to add inner tubes with tubeless sealant and I’ve been having fewer problems. My question is, should I still pressurize both tires with no more than 75 psi?

A: The Enve 3.4 AR is a hookless rim, so, correct, you should never go above 75 psi. Without knowing what size tires you’re using, I can’t offer any further suggestions on exact pressure. I would say start with whatever the Enve or SRAM tire-pressure guide says. The internal width on that rim is 25mm, so it adds a lot of volume.

Just because you’re using an inner tube doesn’t mean you want to run more air pressure. Optimized pressure is all about air volume, and adding a tube only slightly reduces it. This means with or without a tube you should be within only a few psi. For example, if you have a 30mm tire, you might run 55–58 psi. Same rim, same tire but with a tube, I would run 57–60 psi. Adding sealant to a tube is fine but doesn’t offer the same protection that it does when tubeless. It can still heal very small punctures, but tubes tend to tear when they are punctured. This will lead to an even bigger mess than you might get from the same puncture if it was tubeless.

The other problem with the tube is that the risk of a pinch flat goes way up. I always run low pressures because the ambient air temp almost always goes up, and that means tire pressure goes up, too. As crazy as it seems and might not “feel” like it, a bit low is faster than too high. Zipp (SRAM) did a huge study on this and found 1 psi over optimum pressure had a 5–7-watt drop in efficiency, but 10 psi under was only 3–4 watts slower than optimum. Running 2–5 psi over was so significant, they likened it to riding with a parachute. In other words, avoid over-inflating your tires!

I rarely ever start a ride without checking the air pressure. This is the reason I really love the Bluetooth-reliant Quarq Tyrewiz. Spin the wheels, and you get a green light or red light. If setup correctly, you don’t even need a gauge, just pump until you see green and go.

For sure certain tires lose air faster than others. If the leaking continues, consider a different tire or brand. In general, the lighter-weight “race” tubeless tires have this issue because they have less rubber to seal them. They rely more heavily on sealant. My best advice is to experiment with different pressures, and remember, feeling fast does not always mean you’re going the fastest.

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