Are hookless rims safe for road cycling? Here's what the bike industry thinks

Just when it appeared as if the whole debate about hookless rims was dying down, the topic has been thrust back into the spotlight in recent weeks following recent product launches and comments from influential people within the bike industry.

Tadej Pogačar, for example, dominated this year’s Tour de France while making extensive use of ENVE’s new SES 4.5 Pro wheelset – which saw hooked rims make a high-profile return to the brand’s road line-up.

Midway through the Tour, Josh Poertner, CEO of Silca and the former chairman of the Bicycle Wheel Technical Committee, also issued a strong rebuttal of the case for hookless rims in road cycling, calling them “a scam” and claiming they present “a safety risk” to riders.

Though Poertner later sought to clarify his statements in a video posted on Silca’s YouTube channel, saying “scam was a bit of a strong word”, he nevertheless laid out in detail why he feels the claimed benefits of hookless rims don’t stand up to scrutiny.

In light of this, I contacted a number of brands and figures within the bike industry with the aim of taking the temperature of the situation and finding out where things are headed from here.

Thanks to all of the generous responses from those I talked to, I’ve got plenty of insight to share on the topic.

In the coming weeks, we’ll explore whether or not hookless rims have any advantages compared to hooked ones, and what the future holds for this tech.

Here, though, we’re going to take a deep dive into whether hookless rims for road bikes are safe, whether the current international standards are suitable, the issue of rider education and – most importantly – the best practice for using hookless rims if you have a set, or are considering buying one.

Are hookless rims safe for road cycling?

Regardless of questions of performance or value, the most important question in this debate is one of safety.

A key thrust of Poertner’s argument against hookless rims for road cycling is that, in his view, they don’t allow enough margin for error to account for things such as inaccurate pumps, variation in road bike tyre sizes and – perhaps most critically – the fact that riders may make mistakes.

This is critical as exceeding the limitations of your wheels (more on this later) could cause your tyres to blow off your rims.

Speaking to BikeRadar, Poertner said, “Your average floor pump has a [pressure] gauge that’s +/- 5 per cent accurate, and most gauge mechanisms, either bourdon tube or diaphragm, will strain harden over time, so they will begin reading lower than actual pressure.”

Testing my pumps – an old Topeak Joe Blow Sport and a newer Lezyne Alloy Floor Drive – using a Topeak Shuttle digital pressure gauge, showed the analogue gauges on both pumps over-reported tyre pressure by around 6 and 3 per cent, respectively.

This meant the actual pressure in the tyre was slightly lower than each pump indicated, according to the digital gauge.

It’s worth noting that Topeak doesn’t quote a specific accuracy rating for the Shuttle digital gauge, but it nevertheless adds some weight to Poertner’s sentiment that many bike pumps aren't accurate.

While my pumps over-reported, the risk is that an under-reporting pump could lead a rider to unintentionally inflate their tyres beyond the 72.5 psi / 5 bar upper limit mandated by the International Organization for Standardization (ISO) and European Tyre and Rim Technical Organisation (ETRTO).

Compounding this, Poertner also echoed Continental’s recent statements that it is “essential” to consider how changes in ambient temperature affects tyre pressure when using hookless rims.

The German brand suggests that for every 10 degree celsius increase in ambient temperature, your tyre pressure increases by roughly 2.5 psi / 0.17 bar.

Inflating your tyres in a cold garage with an inaccurate pump, prior to a ride on a hot summer’s day could, for example, lead to a significant and potentially dangerous increase in tyre pressure if it pushes you further over the safe limit.

Poertner says that experience from his own rolling resistance testing has shown some tubeless road bike tyres blow off certain hookless rims “at 78-80 psi”, giving a potential margin for error of just 7.6 per cent in a worst-case scenario.

Enhanced testing protocols

Many brands producing hookless rims for road bikes counter these claims, however, by pointing to internal safety testing that goes above and beyond what is required by current international standards (more on these shortly).

Hunt and ENVE, for example, said their blow-off tests for hookless rims go to 150 per cent and “a minimum of 160 per cent” of the ETRTO pressure limit, respectively.

Both brands said this affords riders sufficient margin for error to account for scenarios like those Poertner describes.

ENVE's vice president of product and brand, Jake Patone, noted the brand’s SES tubeless tyres “and nearly all the other tyres we test and approve will achieve pressures of 140 psi / 9.6 bar to 160 psi / 11 bar before tyre blow-off occurs.”

Giant likewise says the safety tests for its Giant- and Cadex-branded hookless rims include inflating tyres up to “1.5 times the recommended maximum pressure”, and ensuring the tyre can “withstand this pressure for 24 hours without blowing off”, amongst other things.

Giant also maintains a list of tyres which have passed or failed this test on its website.

Hunt’s senior development engineer, Patrick Brown, told BikeRadar, “We’re very confident in our system… It's been a very, very long time since I have seen any of our products fail one of these tests.”

He also claimed “most tyre manufacturers” Hunt works with are now testing tubeless tyres to similar levels.

According to Brown, Hunt “worked very closely" with German bicycle tyre specialists, Schwalbe, to “mimic” some of the technology and testing standards it uses, and ensure its tubeless-ready rims (hookless or otherwise) are both safe and easy to use.

Brown also says there’s more to rim safety than simply hooked versus hookless, citing that “sidewall flex on a super lightweight [hooked] rim” can mean the hooks don’t exert the kind of retaining force on a tyre bead one might expect, and that the blow-off point could be similar to that on a hookless rim.

Pantone also echoed this sentiment, saying “safety is our number one priority and the existence of a hooked-bead doesn't inherently deliver a safer product than one that is hookless.”

Are the current standards for hookless rims and tyres suitable?

Where Pantone feels there’s room for improvement, however, is with the current international standards for blow-off testing.

The ISO and ETRTO standards for hookless rims determine rim dimensions, maximum permitted tyre pressures, minimum blow-off pressures and minimum tyre sizes for different internal rim widths.

A hookless rim must, for example, have a minimum internal width of 19mm, with a ‘drop-center’ width of at least 7mm and rim flanks that are at least 5.5mm tall.

On a rim with a 19mm internal width, the minimum nominal tyre size is 22mm (or 22-622, to use the ETRTO size code).

But, on wider rims, the minimum tyre width increases.

23mm-wide rims, for example, require 28mm / 28-622 tyres, while 25mm-wide rims must be used with at least 29mm / 29-622 tyres, and so on.

Likewise, the maximum permitted tyre pressure for hookless rims is, as previously noted, 72.5 psi / 5 bar, and tyres must be able to resist blow-offs at a minimum of 110 per cent of that pressure (79.75 psi / 5.5 bar).

Though it’s not often reported, it’s also worth noting the 72.5 psi / 5 bar maximum pressure applies only to nominal tyre sizes from 25 to 29mm.

Larger tyres have progressively lower maximum inflation pressures on hookless rims, with 30 to 34mm tyres having an upper limit of 65 psi / 4.5 bar, and so on. If you’re running 45 to 54mm gravel bike tyres, for example, the maximum permitted pressure is 43.5 psi / 3 bar.

In any case, the fact some rim and tyre manufacturers are going above and beyond these minimum required standards with their safety testing implies they believe the current standards aren’t good enough.

As noted by Dan Bigham (head of engineering at Red Bull – BORA – hansgrohe), following Thomas De Gendt’s infamous tyre blow-off at the 2024 UAE Tour, testing to just 110 per cent of the maximum permitted pressure means the minimum required “factor of safety” for hookless rims is just 1.1.

Given this, and the example outlined by Poertner above, involving potentially inaccurate pumps and the influence of ambient temperature on tyre pressures, it appears the margin for error can be very small in certain scenarios – even with a technically ‘correct’ setup.

Pantone insisted current ENVE hookless rims are safe to use with tyres on its “approved/recommended” list, saying they “will stay on the rim at pressures far in excess of the ETRTO recommended maximum.”

Nevertheless, he said that ENVE, Zipp, Giant and others have “moved well beyond the [existing] ISO test”, and that “there needs to be a new ISO standard blow-off test that meets the current standard we are testing to.”

The problem with tyre size

Another issue in this area, Poertner says, is the lack of a true industry standard for sizing bicycle tyres.

Citing data gathered by bicyclerollingresistance.com, Poertner says that “currently the sidewall printed number is meaningless” as tyres labelled as 700x28c / 28-622 can actually vary in casing width by up to 7mm.

This is a problem, Poertner says, because ”as the rim gets wider, the narrower casing width tyres will blow off at lower pressures”, as the radially inward pressure pushing the tyre into the rim is reduced.

Poertner provided the above diagram to illustrate this point.

In contrast, hooked rims are typically able to withstand relatively high tyre inflation pressures even with narrower tyres. In Poertner’s experience, “you can generally safely get to 125 per cent of the max stated air pressure when you have a tyre that is 3mm wider than the inner bead width of the rim.”

Poertner suggests moving away from determining nominal tyre sizes in reference to predetermined internal rim widths, which tend to change over time. 25-30mm road bike tyres used to be sized around 17mm-wide rims up to 2019, for example, but now use 19-21mm rims as a reference point.

Instead, Poertner believes the industry should use something like the ‘dD Standard’ proposed by John Deetz some “20 years ago” – which measures the “unmounted casing lay-flat width” of a tyre.

This, Poertner says, would enable riders to make better informed decisions about what tyres are (or aren’t) safe to use on their rims.

What’s holding the bike industry back from improved hookless standards?

It seems, then, an open and shut case that the bike industry needs improved standards for hookless rim testing.

Unfortunately, though, it seems agreeing on any new standards isn’t a straightforward process.

Brown, for example, noted Hunt isn’t part of the group that determines the ISO or ETRTO standards, and it therefore hasn’t “got the ability to steer it at this point in time”, even if it wanted to.

Nevertheless, Brown said he’d “never seen a Schwalbe tyre derailment”, so “it is possible [to have improved blow-off standards on hookless rims] with the correct tyre bead core technology and rim interface, and if everyone’s playing by the same rules.”

Unfortunately, though, Brown said he believed that “the standard hasn't moved on because some tyre manufacturers on that ETRTO board are struggling without the hook for tyre retention.”

Rider education

While it’s possible for riders to end up “flying too close to the sun”, as Poertner describes it, without doing anything technically ‘wrong’, an enormous issue with hookless rims for road bikes is that riders may unknowingly make setup errors.

I’ve lost count of the amount of comments and direct messages I’ve had from people saying they are using or have used unapproved tyre and hookless rim combinations, since I first started reporting on hookless rims in 2020 (while doing a long-term review of Giant’s TCR Advanced Pro 2 Disc).

Most simply want to check whether their setup is safe or not – a question which I’m always happy to attempt to answer – but some will boldly declare something along the lines of “Well I’ve used X tyre on X rim and have never had any issues, so I don’t see what all the fuss is about.”

In the early days of road hookless, ‘X tyre’ was typically Continental’s GP5000 TL – a tyre which was expressly not approved for use on hookless rims (unlike its successor, the GP5000 S TR).

Although with far more hookless-compatible road bike tyres now available, the phenomenon exists to this day – and tyre pressure, as well as tyre size and rim width compatibility, seems to be what catches people out.

Dr Xavier Disley, the director of AeroCoach, says “Hookless rims currently are confusing for consumers”, because riders often aren’t aware of their limitations surrounding tyre pressures.

Poertner says he meets “people at events all the time, who ask us for pressures that they can't run on their wheels – and I've almost never had anybody in those situations know that they had hookless rims.”

Pointing to the example of a rider who emailed his Marginal Gains podcast – who was asking a highly detailed question about tyre setup for a set of hookless rims – Poertner points out that even experienced and knowledgeable riders can easily get things wrong and end up with a potentially dangerous setup.

In that case, the rider was using a 25mm tyre on a hookless rim with a 23mm internal width – a combination which falls outside of the current ISO and ETRTO standards because the tyre is too narrow.

Poertner says the rider thought it was fine to use because the tyre measured 28mm-wide when installed on the rim, but as noted earlier, Poertner says it’s the overall tyre casing width that counts here, not the width of the inflated tyre on a rim.

Best practice for using hookless rims on road bikes

If you’ve got a set of hookless rims on your road bike, the most important thing to do is to ensure you’re sticking within the prescribed limitations of your setup.

That means you must be running hookless-compatible tubeless tyres, following the ISO and ETRTO guidelines with regards to rim width and tyre size, and not exceeding a maximum pressure of 72.5 psi / 5 bar.

If I wanted to run tyre pressures close to that limit, I would also strongly consider switching up to larger tyres to afford myself additional margin for error. Even staunch advocates of hooked rims, such as Poertner and DT Swiss, agreed larger tyres run at lower pressures are generally safer on hookless rims.

It’s worth checking your pump against a digital gauge to understand how accurate it may or may not be.

If you’re considering purchasing a hookless wheelset, then I’d recommend shopping with a reputable brand that is open about its safety testing procedures, and ideally goes above and beyond the ISO minimums – such as one of those mentioned in this article.

For what it's worth, I own a set of Giant carbon wheels with hookless rims and am confident in using those with a set of tyres on its approved list, within the sizing limitations and pressure laid out by the ETRTO.

I would think twice about using tyres that don’t appear on its approved list, though, and would not use tyres that had explicitly failed its tests under any circumstances.

Lastly, if you have any doubts about whether your setup is correct, then you should ask for advice before heading out on the bike – either here in the comment sections below, or directly to the rim or tyre brand in question.

Next time…

In the next instalment of this series, we’ll look at whether or not hookless rims offer any advantages – in terms of performance, durability or cost – compared to hooked rims. Watch this space.