Technical FAQ: Hooked vs. hookless rims, tire choice, and pressure recommendations
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Two questions on hookless rims
Can you discuss rim profiles and how one can identify the different types? Of particular interest is hooked vs. hookless rims, and what the different manufacturers produce, noting that some types of tubeless tires require hooked rims. (See here.)
Could you help me understand tire options that can be used with hookless road wheel designs? I am cross-shopping various road wheelsets, including the Roval CLX 50 Disc and the ENVE SES 4.5 AR Disc.
Both of these are “hookless” carbon rims. ENVE does not recommend using standard clinchers with the 4.5 ARs. In fact, their tech support indicates that “a rim with a hookless bead requires a tubeless-specific tire to create the proper seal between the rim and tire. A standard clincher tire does not pair well with a hookless rim because the rim/tire interface and seal is not perfect. It’s likely that a clincher tire would blow off a hookless SES 4.5 AR rim, so therefore we obviously do not recommend it.”
On the other hand, Roval does not appear to provide a similar warning. A few articles by industry insiders seem to indicate that hookless designs are not at any greater risk of tire blow-offs than hooked rims, but they do not specify whether that only holds true if tubeless-specific tires are used. There are anecdotal accounts on various forums of people using standard tires with hookless wheels, but that provides little in terms of specific info.
While there seems to be a consensus that using standard, non-tubeless tires in a tubeless set-up is a recipe for disaster, what about using standard non-tubeless clinchers with a tube on a hookless rim? Is there really a risk of blow-off because of the design? Or would there be anything specific about ENVE’s design that would make it more prone to such issues (and Roval’s design less so)?
Dear Claude and Ray,
The link that Ray sent provides one answer to Ray’s question about using hookless rims with and without inner tubes. See the illustrations in that link for the distinction between hook- and hookless-bead rims.
While automobile rims generally don’t have hooks, they have been the design of choice for bicycles. Bicycle tires, have, of course, much thinner casings than car tires and are much less stiff. And, like so many of the innovations appearing on road bikes over the past few decades (tubeless tires, oversized tubing, lug-less construction, sloping top tubes, disc brakes, etc.), hookless-bead rims were first introduced on mountain bikes.
For mountain bikes (and, I suppose, for cars), a hookless rim is lighter, and its thicker, lower edge withstands impacts better than a hook-bead rim of the same width and construction. Some hookless rim manufacturers argue that it can allow the use of a smaller, lighter tire and improve its performance, because the inner rim width is greater for the same outer rim width, creating a broader tire stance than a bead hook would allow. This stiffens the tire’s sidewalls for better cornering—a round shape resists torsion more than a bulb-shaped tire (in cross-section) does.
The question is, can road rims for high-pressure clincher tires have an internal rim shape that allows easy tire mounting with bombproof tire retention without a hook in the rim wall to hang onto the tire bead? To work properly, a hookless rim requires a bead lock (a raised inner edge of the rim’s bead shelf, like the “hump” on tubeless-specific rims), as well as strictly-held tolerances of the rim’s wall width, the diameter of the tire bead, and of the rim’s bead shelf to prevent the tire bead from being pushed inward, away from the rim wall during hard cornering. It also requires precision of the central shape of the rim valley, whose width needs to be just wide enough to fit both beads of the tire, and whose circumference needs to be just small enough to allow the tire beads to stretch over the rim walls and just big enough, and with just the right slope to its ramps, that it seals a tubeless tire’s beads.
If you’ve ever seen a tire shop install a car tire on a rim, you can appreciate these dimensional issues. Just like with the car tire, compressed air blasted in through the valve must not escape out from under the bead and must instead push the tire beads up the ramps of the rim valley, over the bead lock, onto the bead seat, and firmly up against the rim walls.
Here are some comments on this subject from some tire and rim brands.
From Specialized’s tire division:
“The current version of the ETRTO (European Tire and Rim Technical Organization) states that, for tires with a max pressure above 5.5bar (80psi), there must be a rim hook.
“Our own testing of high-pressure tires on solid steel rims confirms the ETRTO standard. We made two solid steel rims following ETRTO standard. One rim was a crochet type with bead hooks. The other one was a straight-wall design without the bead hooks. The same tires on a steel rim with bead hook held 20 percent more pressure compared to a straight wall steel rim. (Note that we use steel rims to eliminate any other influences like the reduction of wheel diameter under tire pressure.) This is for max-pressure testing of tube-type clincher tires with tube.
“We find similar results for tubeless clinchers. The straight wall rims decrease the pressure capacity. Rims with a bead hook keep tires on rims up to higher pressures.
“Tire design in tubeless tires plays a more important role than in tube-type clinchers. This amplifies the importance of bead hooks. We find greater variance between tubeless tires than between different tube-type clinchers.
“In summary, straight wall rims show lower burst pressure compared to hooked rims. Some tubeless tires decrease the burst pressure further by way of their bead material or bead layout.
“We do not recommend using any tires with a max pressure above 5.5bar (80psi) on straight wall rims.”
Wolf Vorm Walde
Specialized Tire Product Manager
From Alto Cycling:
“We’ve been offering a complete hookless lineup with our CCX rim models since the end of 2017, with the ability to use any tire model (tubeless or standard clincher), with or without a tube, and with a maximum pressure of 100psi for a 23c tire.
“There are multiple variables that go into designing a hookless profile that will retain every tire bead shape, as well as allow for the use of a tube. This includes the depths of the relief channel as it relates to the depth of the locking channel, the slope of the relief channel ramp, the height of the relief channel peak, the height of the sidewall, etc. I don’t know these details well enough on the ENVE and Roval models to know why Roval will allow for the use of a standard clincher while ENVE will not, but I do know that we designed these variables at Alto with the intent of being able to use any tire model. That’s important for customers who may not be keen to accept tubeless technology just yet, and also for those who are using tubeless setups but need to install a tube if they puncture out on the road, and the sealant doesn’t do its job.
“There are two risks that we’ve come across while setting up our tubeless rims with standard clincher tires (with tubes), but they are both risks when it comes to tire installation on standard hooked rims as well. The first is that you always want to ensure that the tube is not underneath the tire bead prior to inflating it. It’s worth the extra few moments to go around the edge of the tire and inspect it to ensure that the tube is centered. If you inflate the tube while a portion of it is underneath the tire bead, then the tire will blow off the rim every time. The second important item to note, which is true for tubeless or non-tubeless tires, is that the locking channel needs to be smooth and free of debris or wrinkles in the rim tape. Our proprietary rim tape is extremely thin and comes pre-installed on all of our rims. It conforms to the rim and gives the tire bead a smooth channel to press into. It’s important that you don’t remove it and use a thicker nylon strip, and that you do not wrinkle the tape in the locking channel. A wrinkle will mean that the tire bead is not able to sit flush and lock into place, which can cause it to lift up and over the sidewall. That is essentially the only risk involved with hookless rims that wouldn’t be quite as crucial on hooked models, as a tape wrinkle likely wouldn’t cause any issues with a hooked rim.
“We manufacture these hookless rims because they offer significant performance benefits and a range of versatility that our hooked models simply can’t match. The increased tire volume and decreased rolling resistance, along with the added lateral stiffness of the tire itself (due to its inflated shape) offer a ride quality that can’t be matched. Not to mention, our CCX rim models are some of the lightest on the planet, ranging from 365 grams to 440 grams depending on depth. I actually did a nice podcast with VeloNews about six months ago regarding some of these benefits, and a lot of really good questions were asked.
“It’s important to note, however, that this increased tire volume does mean that the tires should be run at lower pressures in order to get the same hoop stress and tire feel as you’d be accustomed to with that same tire size on a hooked rim. A 25c tire on our CCX40 rim will inflate to a width of 27.5 millimeters, while on our hooked rim it will be 26 millimeters. This added volume means that you’ll want to run it at roughly 84psi in order to create the same road feel as you’d experience at 96psi on our CC40 hooked rim. I’ve attached our recommended tire pressure chart, which is based on rider weight and tire size.
“Even though these lower pressures on our CCX rims have an equivalent road feel to high pressures on hooked models, we do have many customers in the triathlon market who refuse to run pressures below 120psi. We recently launched our CCX311 disc, as well as the CCX86 rim. One of the major questions was whether or not we would carry forward our hookless rim profile to those two models, and it’s something that we debated internally for quite a while. The hookless profile is awesome to allow for a huge range of tire sizes, but there likely won’t be anyone out there using the CCX86’s with 40c tires for gravel grinding. So, we decided to split our CCX line right down the middle: The CCX28 and CCX40 will remain unchanged: super lightweight and hookless for road and gravel use, and will be renamed CCX28HL and CCX40HL. The CCX86 rim and CCX311 have hooked profiles to allow for extremely high pressure use if the rider wants it, and we have a new hooked CCX52 model to match it. The hookless CCX52 rim is still in stock and being sold, but it will likely be phased out in the coming months as we transition over to the new profile. We still own the slider for the hookless mold, so if anyone special orders a CCX52HL wheel set, we will be able to do it with a certain lead time.”
Alto Cycling co-founder
From ENVE Composites:
“This is a great question, moreover, it makes us very happy when we see that riders are paying attention to these types of details to ensure that the tires they are pairing with their rims will result in a safe ride. To answer your question, it may be best to answer the question of “Why hookless?” Essentially, our hookless rim designs exist as a result of our desire to refine the tubeless (road, mountain, or gravel) experience, and to achieve better aerodynamics in the case of our SES AR wheel models. By going hookless, we can mold rims to more exacting tolerances, which in turn results in easier tubeless setups, air retention, and ultimately tire retention. On the flip side, a rim with a hook-bead exists to retain tires that could “stretch” off the rim. Hook-beads really gained popularity when tire manufacturers began producing folding tires that were lighter and faster rolling than their non-folding bead counterparts, but consequently less precise in terms of bead diameters. To solve the problem, hook-beads were introduced to retain the tire and prevent it from coming off the rim. Fast forward to today, a properly built tubeless tire has a defined bead seat diameter and ideally should not stretch off the bead seat of the rim. The idea with tubeless is that you have a seal between the tire and the rim on the rim’s bead seat (the shoulders on either side of the drop center on the rim’s tire bed).
“While some may argue that a hook-bead can act as a seal as well, if a tire has stretched off the bead seat diameter and achieved a seal on the hook-bead, there will be no lateral support of the tire, so lateral pressure on the tire can result in “burping” which is the unexpected loss of air. This is why the mountain bike world committed to hookless five years ago. So, back to tires. For the reasons alluded to previously, ENVE recommends that riders should only use tubeless tires. ENVE has a list of approved tires on our website, as not all tubeless tires are created equally in terms of bead stiffness and therefore retention.
“See below for more on tires approved for our SES AR hookless rims, as these tires will guarantee a proper interface with the rim’s bead seat diameter, which means a better and safer ride experience. While there are some non-tubeless folding tires which have beads stiff enough to ensure retention on a hookless rim with an inner-tube, at the end of the day, this is simply not what the modern hookless rim was designed for. If someone wishes to use an inner tube with a hookless ENVE rim, they are welcome to do so as long as the tire is on our approved tubeless tire list. Finally, it is important to pay attention to the rim and tire manufacturer’s maximum tire pressure ratings and if there is a difference between two max pressures, one should always default to the lower of the two pressures.”
ENVE, VP of Product and Consumer Experience
Click here for a list of approves tires for use with its SES AR hookless rims:
Lennard Zinn, our longtime technical writer, joined VeloNews in 1987. He is also a custom frame builder (www.zinncycles.com) and purveyor of non-custom huge bikes (bikeclydesdale.com), a former U.S. national team rider, co-author of “The Haywire Heart,” and author of many bicycle books including “Zinn and the Art of Road Bike Maintenance,” as well as “Zinn and the Art of Triathlon Bikes” and “Zinn’s Cycling Primer: Maintenance Tips and Skill Building for Cyclists.” He holds a bachelor’s in physics from Colorado College.