To be honest, when Zipp reached out to schedule a video chat about tubeless, hookless rims for road bikes, I wondered what was up their sleeve. After all, we’ve kinda covered hookless rim designs.
And they explained their design decisions when the latest 303 Firecrest wheels launched. ENVE gave us their thoughts on it, too. And we’ve seen designs from a number of brands pop up in the last couple of years, slowly giving credence to the idea that higher pressure road bike tires will, in fact, work just fine on hookless tubeless rims.
So, what’s new here?
Well, it’s a video interview for one, but there’ve also been updates to ETRTO and ISO standards that are bringing everyone closer to a level starting point. Which means safer Road Tubeless designs for all of us, and better cross compatibility between rims and tire brands. That’s a big part of our discussion with Bastien Donzé, Zipp’s wheel product manager.
Here are a few of the slides from our call:
What is a Hookless rim standard?
Above is a snapshot of the ETRTO reference drawings with measurements and tolerances for “Tubeless Straight Side” rims, more commonly known as “Hookless” rims. Click any image to enlarge.
Here’s the rim drawing portion enlarged. It’s worth noting that bicycles are basically the last type of transportation relying on wheels to use hooked rim designs. Cars, motorcycles, even airplanes, all use hookless rims. And all of those carry much higher weights under much higher loads and forces.
Word on the streets is that these measurements are basically approved by ISO, too, they just haven’t published them yet. Where ETRTO is technically a European standard (even though many companies in other countries adhere to it so that their goods are marketable in Europe), ISO is an international standard.
How much tire pressure can I put on a hookless rim?
This chart shows their “Burst Pressure” tests, illustrating how high the pressure has to be to blow a tire off of a hookless rim. Tire and rim measurements shown at top, and each point on the black line is a different tire.
They found only one outlier that blew off at a lower pressure…but for reference 10 Bar = 145psi. So, most tires held in place up to almost 200psi. Given that most rim brands are recommending lower tire pressures (Zipp has a recommended max of just 73psi on their new 303 Firecrest rims), you’re unlikely to ever blow a tire off the rim.
They provided their tire pressure recommendation chart with the launch of the 303 S wheels, which graphs rider weight versus tire width.
Which road bike tires are approved for hookless rims?
That’s the question Zipp gets the most: Which tires can you mount on hookless rims. And it’s one where their answer differs from some other wheel and rim brands.
Whereas some, like ENVE, are testing tires in house, Zipp’s sending rims to the tire brands and asking them to certify whether they’re approved or not. Which makes sense, because ultimately, it’s up to each brand to certify their own products, but here’s the caveat / good news:
As long as both parties are adhering to the ETRTO and, soon, the ISO standards, then all brands should work great with each other. In fact, Zipp says that if a tire is made to ETRTO Tubeless-Ready standards, then it should work just fine on their new hookless rims. If you’re in doubt, ask the tire brand if they’re up to standards.
Our take? Seems like there should be a little logo or hot patch that goes on rims and tires to indicate if they meet those standards, giving all us riders a quick, easy to understand visual confirmation that they’re made to work together.
After watching this, what do you think? Are you riding Road Tubeless on hookless rims already? Let us know in the comments!