Time to Relearn Road Tire Pressures - Slowtwitch News (2024)

The next aero wheel you buy will be faster for you than the last, but it’ll be a very different wheel. You’ll pump 65psi in the tire that goes on that wheel – or maybe 60psi – if you want that wheel and tire to perform at their best. You may have a hard time accepting that this is the best pressure for that wheel and tire if you want to go your fastest. Nevertheless, it will be. These new style wheels are going to start launching in 2022.

If you’re still riding a 90psi to 110psi pressure you’re probably running an older wheel with an inner bead width of 20mm or smaller; you’re riding with tubes; your rims have bead hooks; and you may still be riding 23mm tires. This was the case for all of us just a few years ago. But not that many pro triathletes are riding anything but tubeless tires anymore, and it’s not because of sponsor demands. Plus, the brands that championed the hookless rim platform have already revamped their road and gravel lines with rims of this type. The only thing left for them to make is their aero wheels.

The expanded inner bead widths of today’s new rims, combined with the larger tires now becoming fashionable in tri and road, and hookless beads on rims, conspire to bring the ideal pressure down. Yes, hookless beads are coming to aero wheels (cue the wailing and gnashing of teeth), and now is the time to educate yourself on them.

Let’s be clear. One of the reasons these brands waited this long to launch their aero wheels with hookless beads is because they’re concerned you’re not going to like what I’ve just written above about tire pressures. But hear me out. Rock hard tires are no longer the fastest tires (if they ever were). Tires with more volume get hard to the touch on much less pressure. Not only are wider tires becoming the norm in road and tri, wider bead widths and deeper rim wells grow the total volume of air in the wheel/tire system. Here’s a term for you: Spring rate. Pneumatic tires are springs, and like all springs they deflect or depress as you weight them. Spring rate is measurable, as in, inches or millimeters per pound or kilogram of weight applied. The larger the volume of air in a tire the less air you need in that tire to achieve a similar spring rate.

For you shoe dogs, a good analogy would be durometer. When considering what foam to put in the midsole of a run shoe, denser foam gives you less deflection when you hit the ground (it’s a harder shoe); less dense foam gives you a softer ride. It deflects more when you impact the ground. Tires are like run shoes: You don’t want the ride too hard; nor too soft. Even these supershoes, with their superfoam, don’t rely on rock hardness.

Because the volume is these wheels and tires is high, the pressure is less to achieve the same spring rate (or durometer if you prefer).

Now, back to hookless beads for a moment. The ETRTO is the European governing body on tires. Any tires. Airplane to wheelbarrow. Including bikes. Funny thing, these folks have very little to say to tire companies. Instead, they mostly tell wheel companies what to make, and the tire companies conform to wheels made to the ETRTO’s printed standards. This is good, because tire companies know exactly how to make their tires. Wheel companies don’t really have a choice, because they know how the tires are going to be made and if the tire blows off the rim or the rim cuts into the tire’s bead or sidewall it’s because the wheel maker didn’t conform to the ETRTO manual.

In 2022 the ETRTO will publish a set of tire ranges for given inner bead widths and here’s what surprised me: Those ranges are the same for wheels with hooked and hookless beads. The only difference is that the ETRTO has very precise contours for rims made for hookless tires; and there’s a pressure limit on hookless beads: 72.5psi.

To me, that 72.5psi is an arbitrarily round number. That’s not a very “round” number you might say, but, that’s because the ETRTO didn’t choose a number measured in psi, but in kilopascals. You know, that measure we all use daily. When my wife says I’m full of hot air and I ask for clarity she says, “500 kilopascals, that’s how much air you’re full of.” Which is exactly what the ETRTO said. Tires with hookless beads should not be used with pressure above 500kPa. Had hookless beads been introduced 5 years ago, this would’ve been a problem, because a 23mm tire going onto a rim measuring 19mm from bead-to-bead doesn’t have enough air volume. More pressure would be needed in that tire.

But today, not a problem. You can go on our Reader Forum and hear all kinds of tubeless woes from users, but, things have changed a lot in the last 2 years if you use both wheels and tires made in the last 2 years. The first tires and wheels made that conform to ETRTO specs for tubeless road tires were introduced in 2019, and today’s rims – with hooked and hookless beads – matched to the tires that have come out since 2019, make for dreamy riding.

My next article on this will contain a list of the ETRTO’s rim specs and the tires that the ETRTO says will mate to them. I’ll limit this specifically to hookless, because the list is manageable and because a number of the wheels coming out this year that you’ll want to read about have hookless beads. I’ll write to you what wheels are already out and what tires – make, model and size – are compatible with them. As we move toward spring I’ll write what pressures you should put in those tires. As the new wheels and tires come to market I’ll write about those as well.

We have a discussion thread on our Reader Forum, approaching 500 posts as of this writing, devoted to road tubeless. That thread is going to get a lot larger I predict, and we will curate that thread and attempt to answer any questions any of you have or will have.

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