Tubeless road wheels won't pump past 80 psi

Question

I bought new Bontrager Aeolus XXX TLR Tubeless Road wheel set and had them put together by A Trek bike shop. They supposedly put in the right amount of sealant but when I pump them up past 80 PSI they immediately decompress back down to about 80 PSI . I rode them at the 80 PSI and they felt good but the rear tire down to 40 PSI at end of 60 miles.

One thing I worry about was the bike shop guy insisted on putting the O-ring on the valve even though the instructions specifically said to remove the o-ring for road tires. The reason I took it to the bike shop was I couldn't get either tire to seat.

I was going to add more sealant but didn't know how much to add since I know there is some already in there and didn't want to deflate the wheel fearing the bead would fall off.

Answer 1

Road tubeless tires have a pressure limit of 80-85 psi (depending on who you ask). I'll admit I'm surprised that this limit is self-enforcing in this way.

The fact that you're losing so much pressure in the course of a ride is obviously problematic—the air is getting out somewhere. I don't think you'd be losing that much air through the tire walls. If the tire walls are very porous, you should see a fair amount of sealant weeping through too, and you may need to add sealant until the weeping ends. There are kits for inserting sealant through the valve, if/when you need to do that. Is it possible you're "burping" the tire and losing pressure that way?

Seating the tires often requires a fast inrush of pressure into the tire to pop the beads past the "shoulders" on the floor of the rim; there are special pumps and pressurizable canisters for this exact purpose.

Answer 2

Hesitating because a shop installed the "right amount" of sealant belies the misconception that sealant volume is anything like an exact science. It's actually quite the opposite. Different tire casings can take very different amounts on initial installation before they develop a coating sufficient to hold air effectively. Beyond that, there's a choice best made by the cyclist on how much free liquid sealant you want sloshing around inside. More gives you faster and bigger puncture fill and/or a longer maintenance interval, but at the expense of weight.

Air pressure going low over the course of a ride or a day is usually caused by needing more sealant. In your situation, if you're trying to be kind of weight-minimal and presuming you've got tires in the 25-28mm range, I would open the valves up and start by injecting around 1oz/30ml each, with the goal of getting a bit better coating and then having some modest free liquid on top of that. If you want to go a little longer without having to mess with it, double that volume.

Shops do their best to choose an appropriate sealant amount for any given situation (install, maintenance refill, etc) but there's guesswork involved. What sometimes goes unsaid, and often does in marketing and product info, is that to be an effective tubeless user you need to develop your own rhythm with sealant fill quantities and timing, based on your own equipment, conditions, and weight vs hassle priorities. Also, in my experience those o-rings make a pretty marginal difference either way. They're not the primary seal and things have already gone way wrong if you're losing air out of them. I don't know why they left it on if instructions said otherwise, but it's possible they had experience that contradicted the instructions. Try it both ways and see if you can tell a difference, or maybe check back in with them to see if they know something specific to those rims.