Safety Advice: Non-Standard Rims and Rene Herse Tires

Safety advice: Rene Herse tires are designed for rims that meet the ETRTO standard, specifically:

  • G height: 5.2 – 6.5 mm
  • Sidewalls with hooks.

Rims that do not meet the current standards – especially hookless rims and rims with sidewalls that have G heights of less than 5.0 mm – are not recommended for use with Rene Herse tires. This is especially important when installing your tires tubeless. Our testing has found that tires mounted tubeless on hookless rims or on rims with lower-than-standard G heights have a less-than-adequate margin of safety against blow-offs. All warranties are void when Rene Herse tires are installed on rims that do not meet the current ETRTO standards.

The ETRTO (European Tire and Rim Technical Organization) sets most standards for car and bicycle tires and wheels, not just for Europe, but for the entire world. Currently, the ETRTO standards are the only standards that exist for tubeless bicycle wheels. They specify the G height of the sidewall at 5.2 mm (for tubeless) and 5.5 – 6.5 mm (for tubes, depending on the rim width). The sidewall must have a hook.

Like most tire makers, we design our tires to meet the ETRTO standards. Why don’t all rim makers follow these standards, too?

In the past, there were some poorly designed rims with overly deep wells and G heights larger than 6.5 mm. Fortunately, these rims have long been discontinued, and cyclists who still have them usually know how to deal with the problems that occur when trying to mount tires on them (as much as this is possible).

These days, we see some rims with G heights that are smaller than the ETRTO standard and no hooks. Even though these rims do not meet the current standards, this makes sense for mountain bikes with carbon rims: A tall sidewall makes the rim vulnerable if the tire bottoms out while the bike is leaning over. The tall G height provides a long lever that can crack the rim. Why hookless? Mostly because the hook is difficult to make with carbon fiber: It requires a complex 3-piece mold for the rim bed.

A ‘hookless’ rim (above) with a shorter G height is stronger and less expensive to make. Stiff mountain bike tires are inflated to ultra-low pressures. They won’t blow off their rims even if there isn’t much sidewall to hold them on. So the non-standard rims have worked fine for mountain bikes. These mountain bike rims usually come with low maximum pressure ratings.

Recently, some rim makers have introduced ‘gravel’ or ‘all-road’ rims that are made to mountain bike standards: without hooks and with low G heights. Unfortunately, these rims don’t work well for high-performance all-road tires.

We can’t say it often enough: The bikes we ride aren’t mountain bikes. They are road bikes with really wide tires. Perhaps it’s not surprising that the industry still misunderstands what gravel and all-road riding is all about: The sport has grown from the bottom up, when riders like us headed into the mountains, found new roads and designed new equipment to ride on them. Some of the established manufacturers are getting it, but many still think inside their traditional boxes of ‘Road’ and ‘Mountain’ bikes. More often than not, they’ve put our bikes into the ‘Mountain’ category.

Here at Rene Herse Cycles, we’ve always thought of them as ‘road’ bikes – that is why we coined the term ‘all-road bike’ for them. Even though my Firefly (above) has 26″ wheels, it’s not a drop-bar mountain bike. It’s a road bike with wide tires. We ride on road tires, and we need road rims for them.

That is why hookless mountain bike rims don’t work well for all-road wheels. All-road tires are supple, and they run at higher pressures than mountain bike tires. This requires an additional margin of safety.

We tested a 650B x 48 mm Switchback Hill tire on a carbon mountain bike wheel with a hookless rim and a G height 0f 5.0 mm. We mounted the tire tubeless, but without sealant (for obvious reasons). The rim is rated to 40 psi, and the tire was fine at that pressure. 40 psi isn’t a lot, even for a 48 mm-wide tire. The tire is rated to 55 psi, so we kept inflating to see what would happen. At 58 psi, the tire blew off. We then repeated the experiment with a second tire, and it blew off at 65 psi. This problem is not limited to Rene Herse tires: Other riders have reported similar blow-offs with tires from other makers.

58 psi is a lot of pressure for a 48 mm tire, but when the tolerances stack up in a bad way (slightly oversize tire and slightly undersize rim) or when the tire isn’t installed perfectly, the blow-off pressure will be lower. Then the margin of safety won’t be adequate. This is neither the tire nor the rim’s fault. It’s simply using the wrong rim for a supple all-road tire.

How much of a difference does the hook make? We put one of the tires on a HED Belgium Plus rim. The G height is the same as on the carbon rim we tested (5.0 mm), but the HED rim has a hook. Even though this is the same tire that already had blown off the rim once, it stayed on at 75 psi. The is no doubt: The hook has a crucial function in keeping the tire on the rim. Other rim and tire makers have tested and found the same: The hook significantly increases the pressure at which the tire safely stays on the rim.

Fortunately, there is another way to increase the margin of safety: Use inner tubes. We put the tire back on the hookless mountain bike wheel, this time with a tube. We inflated it to 75 psi and left it overnight. Nothing happened. We were surprised that even the violent explosion had not stretched the tire, but these beads are strong. (However, we don’t recommend re-using a tire that has blown off the rim.) That is good news: Hookless rims tend to work better when used with tubes – even though we cannot officially recommend them, since they don’t meet the ETRTO standards to which our tires are designed

Conclusion: All-road bikes are road bikes, and all-road tires are road tires: They should be mounted on road wheels. When you buy new wheels, make sure the rims are designed to the ETRTO standards, and not to mountain bike standards: You want a hook and a G height of 5.2 – 6.5 mm. If your wheels already are equipped with hookless rims, using tubes can increase your margin of safety. And check the maximum pressure ratings, not just of the tire, but also the rim: Don’t exceed them!

Tubeless is great technology – had I used inner tubes on the ride across Odarumi Pass in Japan (above), I probably would have pinch-flatted several times. But tubeless is also an emerging technology. We’ve had to learn how to mount tires (huge blasts with compressors are a sign that the rim is undersize) and how much sealant we need (more than we usually think). Now we are discovering that hookless mtb-style rims don’t work well with all-road tires.

Why do tubeless tires blow off so much more easily? Without a tube reinforcing the joint between rim and tire, it’s much easier for air pressure to force its way out. It’s still extremely rare for tires to blow off, but, with tubeless tires becoming more popular, there have been more incidents than before. They affect all brands of tires – a little while ago, a wheel maker told me of two different tires from a big German tire maker that had blown off his hookless rims that day.

Also remember that tubeless-compatible tires always need liquid sealant inside. If the sealant dries out completely, the tire can break loose from the rim sidewall and deflate suddenly. This can cause the tire to come off the rim, even if rim and tire are sized correctly.

Safety is our biggest concern, not just for our customers, but also for ourselves, because we ride our bikes hard. We’ll continue to test, and we’ll continue to work with rim makers, to drive tubeless technology forward in a safe and responsible way. The last thing we want to worry about during our adventures is whether our tires will stay on their rims! Fortunately, in almost 100,000 km (60,000 miles) on Rene Herse tires and their predecessors, I’ve not experienced a blowout. We’ll work hard to make it remain that way!

34 Responses to Safety Advice: Non-Standard Rims and Rene Herse Tires

  1. Brian Roth April 10, 2019 at 6:43 am #

    Question: would you endorse the HED Belgian Plus rim, since the G height (5.0 mm) seems to fall just short of the ETRTO minimum of 5.2 mm?

    • Jan Heine April 10, 2019 at 7:18 am #

      All interfaces have some leeway to account for manufacturing tolerances. Our testing of multiple samples has shown that the HED Belgium Plus rims work fine, both tubeless and with tubes, despite their G height being just below the ETRTO standard. Otherwise, we would not sell this rim.

  2. Marius Clore April 10, 2019 at 7:04 am #

    It is certainly very commendable to acknowledge that Compass/Rene Herse tires have an issue with hookless rims. And it is also quite possible that the issue lies with the suppleness of the Compass tires which make them so nice to ride. In this regard is there any difference between the regular and extralight versions.
    That being said, I think it’s a bit of a cop out on the part of Jan. The major manufacturers of high end tubeless carbon wheels have all shifted to hookless even for their road rims. This includes ENVE (see SES 3.4AR and 4.5 AR, as well as the G series for gravel), Zipp and Specialized (the new Roval CLXs). All these manufacturers no doubt sell a large number of wheelsets, and given that these wheelsets are not exactly what one might call cheap, I doubt that saving a few bucks on the mold to eliminate the hook was their major concern.
    I can tell you that in the past I extensively rode Roval Control SL wheels which were hookless with Schwalbe S-one’s (30 mm) at fairly high pressure (80 psi) with absolutely no issue. Further, I’ve never had an issue with either WTB or Schwalbe tubeless compatible/tubeless easy tires on the ENVE G series and SES AR 4.5 wheels either. However, I had three blow outs on the road with Compass tires.
    Now I think it’s fair to see that Compass tires are what one might term a boutique item, and hence extensive testing is probably not possible. However, Panaracer, the manufacturer of Compass tires, makes Gravel King tubeless tires which I imagine exceed the sales of Compass tires by over four order of magnitude. Had their been blow-out issues with Gravel Kings, this would be well known.
    So my suspicion is that the issue with Compass tires probably lies in the nature of the bead itself, rather than the suppleness of the tires. For sure the bead is not as beefy as the Schwalbe G one or WTB beads.
    Perhaps it’s time to actually design fully tubeless ready Compass tires that work safely with hookless rims that are becoming the standard for both road and gravel, even if they don’t follow the ERTO standard.

    • Jan Heine April 10, 2019 at 9:54 am #

      Thank you for your thoughtful comments. Most of all, I am very sorry that you had tires blow off an out-of-standard (and possibly out-of-spec) rim. Your experience was one of those that prompted us to issue this safety advice. I’d like to reply to a few things you mentioned in your comments:

1. Blow-offs are extremely rare. We have thousands of customers running Rene Herse / Compass tires on hookless carbon rims like yours without problems.

      2. There is a lot of discussion in the tire and rim industry on this subject right now. I suspect other tire makers will soon issue their own warnings for their high-performance models. In fact, Challenge already has – you can find their notice here. Mountain bike tires (and tires that are constructed like mountain bike tires) seem to be fine, but they don’t offer the performance that riders like us want from their gravel and all-road bikes.

      3. Blow-offs affect all types of tires. You had good luck with the Schwalbe G-One, but that was one of the tires mentioned in the blog (I didn’t want to name names).

      4. You suspect that the bead of Rene Herse and Panaracer Gravel King tires is different. That is not the case – they are exactly the same. It would have been very costly to develop a different bead for our tires, and we saw no need to change Panaracer’s bead. It’s the casing and tread that is different with our tires, not the bead.

      5. The testing programs of big companies are much smaller than you would think. Just consider: It wasn’t the big companies who figured out how to make wide tires that roll fast. Furthermore, big makers are usually in a rush to bring products to market. That is why there are so many recalls of brand-new products that fail as soon as they are put on the road. All too often, users are the testers. In the case of some rim companies, I’ve heard that they did test their hookless rims with mountain bike tires, where they work fine. Then they migrated that design – now ‘proven’ – to their gravel line without much additional testing.
      6. We have done more testing of our tires with different rims than probably anybody else: Every Bicycle Quarterly test bike is equipped with Rene Herse tires to level the playing field. (Tires have such a great influence on the ride and performance of a bike that we’d be testing tires, not bikes, if our test bikes didn’t have comparable tires.) Despite having mounted more than 150 Rene Herse / Compass tires on a variety of rims (aluminum and carbon) – and ridden them hard – we’ve never experienced a blow-out. (The exception is when we tested tire/rim combinations to the point of blowing out.) You can see all BQ test bikes here.

      7. Finally, there are efforts now to bring the tire and rim makers together and work out standards that will work for all users. We are involved in that, and we’ll push for standards that are safe for all types of tires, not just stiff mountain bike and touring tires.

  3. Marius Clore April 10, 2019 at 7:09 am #

    As as addendum to my previous comment, I would add that I’m pretty sure that ENVE, Specialized and Zipp have tested their tubeless wheelsets extensively (and far more so than anything that Rene Herse could possibly do). In terms of ENVE, many of their gravel wheelsets feature WTB tires on their web site photo shoots, including road and road+ tires. This would suggest that had the rims been an issue they would have experienced blow outs if the WTB tires used weren’t up to scratch and compatible with the new ENVE designs.

    • Jan Heine April 10, 2019 at 10:09 am #

      You mention testing by big companies. I’ve worked for and with big companies in the past: Some are better than others, and it’s not always the ones who spend the most on marketing. It was interesting to see how Enve’s safety warning about tires with cotton casings turned out to be an issue with their rims: They have a really sharp edge that cuts the tires – see this article in Bicycle Retailer and Industry News (BRAIN).
      Of course, everybody wonders why the latest Enve rims have such a sharp edge. There is no conceivable functional reason for it. According to the BRAIN article, an Enve spokesperson said “that he couldn’t comment on the situation.” I suspect it’s as simple as somebody forgetting to specify a radius in the CAD drawing for the rim mold. These things happen even at Rene Herse Cycles, but we usually catch them in our reviews of the drawings before we send them to production.

    • DaveS April 12, 2019 at 10:50 am #

      Please share the details of bicycle manufacture testing that you know. I’m always told about all the great testing they do, but when pressed for details, I’m not given any. I’ve been specifically told several time that this information is proprietary. Interestingly, this has also been used against me when a carbon fork broke and it was not warrantied. One of the reasons was that they did all this testing, so it had to be user error.

      • Marius Clore April 12, 2019 at 2:47 pm #

        Hi Dave,
        I don’t have any details. That being said, there is a lot of design that goes into the high end carbon wheels, and both Zipp and ENVE make their carbon wheels in the US in-house, as opposed to in China/Taiwan (e.g. Specialized).
        All I can say is that I’ve had two sets of Extralight Compass tubeless compatible tires (Bon Jon and Barlow Pass) blow off after a couple of 100 miles (perhaps after hitting a rough patch of road, but not a pothole, in one case, and upon turning in the other) on the new hookless ENVE G23 and M525 wheels. My conclusion is that the tubeless Compass tires, beautifully though they ride, are problematic with the ENVE hookless gravel rims. And clearly Jan feels the same way, hence the safety notice.
        I have not had any issues on these ENVE wheels for several thousand miles on Schwalbe G one speeds (700×35). The beed is a lot beefier on the Schwalbe G one speed, and perhaps that’s part of the reason. And of course the cassing on the Compass tires, especially the Extralight versions, are a lot more supple, which may also contribute.
        Just searching the web, I saw that people had issues with Schwalbe G one Allrounds on American Classic tubeless race wheels which do have hooks, but I’ve never had any experience with American Classic wheels.
        Incidentally, I would think the introduction of hookless rims by both Zipp and ENVE must have more to do with performance and avoidance of pinch flats upon bottoming out than cost. I only say this because both were manufacturing carbon clinchers as well as tubeless wheels with hooks. So they had the technology mastered, and their wheels are not exactly on the cheap side. Indeed, I believe Hunt carbon rims which are half the price have hooks.

        • Jan Heine April 15, 2019 at 11:02 am #

          Marius, I respect your belief that high-end makers always put out the best products. However, I can tell you that two different rim makers told me that the switch to hookless rims was due to cost reasons. It’s not uncommon for enthusiasts to start a company making high-end products, and then to sell them to others who are more interested in the bottom line, and cut costs.
          I ma glad that you have found tires that seem to work well, but please be careful – I know of at least one tire of that model that blew off a hookless rim. Much of it depends on the tolerances – if you have a slightly small wheel and a slightly large tire, things can go wrong. Also, if the sealant inside the tire dries out, there is nothing to ‘glue’ the tire to the rim, and it can break loose from the rim wall. With a history of blowing tires off the same (hookless) rim, I’d recommend using tubes, no matter which tires you run.

  4. snilard April 10, 2019 at 9:56 am #

    Jan, do You have experience with DT Swiss rims?

  5. Jacob Musha April 10, 2019 at 11:09 am #

    What is the rationale for hookless rims, other than a cheaper mold? Talk about obsolete! I remember decades ago when steel rims didn’t have hooks. There were warnings on some tires, even very stiff and heavy ones, that said “use with hook-edged rim only” or (lower) maximum pressures listed for hookless rims.
    This discussion makes me glad I ride a thoroughly Modern Bike – aluminum rims with a hooked bead and brake track built-in, and tubes so I don’t have to deal with sealants and blowouts.

    • Jan Heine April 10, 2019 at 11:25 am #

      I was thinking the same thing – all the first clincher rims were hookless. When clinchers became more supple, hooked rims were required to keep them safely on the rim.

    • Sam Atkinson April 10, 2019 at 11:51 am #

      >”What is the rationale for hookless rims, other than a cheaper mold?”
      Higher strength-to-weight.
      I’d imagine that the easier manufacture isn’t insignificant. Aluminum rims nearly always use hooks, even though hookless would be just as easy to manufacture in aluminum as hooked.
      Making hooks in carbon is tricky. The mold itself isn’t hard to make, but laying up sheets of carbon and epoxy into a small sharp shape like that is. An alternative approach is to use a hookless mold with super-thick walls, and then mill the hooks out of it. But then you’re hacking up the carbon fibers and making for a much weaker structure.

      • Jan Heine April 10, 2019 at 12:25 pm #

        It’s both. As you mention, carbon isn’t well-suited to making shapes like the hook. The three-piece mold is an added complication. For aluminum rims, hookless makes no sense, since the hook is part of the extrusion – which is why most aluminum rims still have hooks.

    • Mike M April 10, 2019 at 1:05 pm #

      @Jacob Musha: I couldn’t agree more. This is just more reason for me to avoid tubeless tech. I’ll stick with my alumin(i)um hooked rims and tubes, thanks. Mitigating the (for me, very small) risk of pinch flats just comes with too many headaches.

  6. Bern April 10, 2019 at 1:46 pm #

    Pro tip:
    When deliberately inflating tires to failure, use water instead of air. FAR safer. Do not ask me how I know.

    • Jan Heine April 10, 2019 at 1:51 pm #

      With really high pressures, that is the way to do it. Since we were using air, we stopped at 85 psi when inflating the tire with a tube. Whether a 48 mm tire blows off at 90 or 150 psi doesn’t make a difference – neither of those pressures are relevant for real use, especially since the tire itself is rated to 55 psi.

  7. Nelson April 10, 2019 at 2:29 pm #

    I can´t see how a hookless rim could be safer then one with hooks.
    I had had only one blowout to date (noc..noc…noc), on a steel hookless rim, near ’77, with a stiff tire, ~60 psi.
    There´s no internal height restriction on ERTRO Standard?

    • Jan Heine April 10, 2019 at 3:43 pm #

      The G height is the height of the sidewall. ETRTO doesn’t allow for a range, but just a single value. That value depends on the width of the rim and whether it’s tubeless or not. It’s between 5.2 mm (tubeless) and 6.5 mm (wide rims with tubes).

  8. Shu-Sin April 11, 2019 at 7:51 am #

    Were the tires loaded (with what would be the weight of the rider and perhaps gear) when you tested them? I would assume that the pressure rises with added weight… and compounded even further, with a sudden spike in pressure, when said tire hits a bump–rider aloft, of course.
    It would seem to me that the chance of blow out would increase exponentially with the combined weight of rider, bicycle, gear, etc. especially when hitting an obstacle at speed: a recipe for disaster!

    • Jan Heine April 11, 2019 at 8:03 am #

      The tires were not weighted, but physics tells us that the weight of the rider and the bumps cause only a minimal increase in pressure. A bigger potential concern is the flexing of the tire if you hit a bump, but in the rare cases when tires have blown off hookless rims, this seems to have occurred either with the bike stationary (bikes spend more time standing than moving) or just rolling along.

  9. Jon Blum April 11, 2019 at 10:44 pm #

    I had some hookless rims (Araya) in the mid-1980s, and I remember the first (and last) time I mounted a Kevlar-beaded tire. Boom! The owner of the shop that sold them to me apologized, and advised me to use only steel-beaded tires. I followed that advice and never had another blowoff. The steel beads are certainly stiffer, and perhaps they stretch a bit less? I think pretty much all high-performance tires today have Kevlar beads; I am not suggesting going back to steel to address this issue.

  10. Nelson Zornitta April 12, 2019 at 6:18 am #

    There is a Mavic article about the topic:

    • Jan Heine April 12, 2019 at 8:41 am #

      It’s nice to see that most of the big rim companies are committed to the ETRTO standards.

  11. Chauncey B Wood April 12, 2019 at 6:46 am #

    Do Stans Crest MK3 rims meet ETRTO standards?

  12. Chauncey B Wood April 12, 2019 at 12:21 pm #

    I asked the folks at Stans No Tubes if their Crest MK3 rims meet ETRTO standards. Here is the reply I got:
    “Ok, so nearly no rims right now fall into this standard. It is a older standard of measurement and it is being revised. They are working with us and other company to create a proper standard. Our rims do have slight hooks at the top on the sidewall.”
    I would love some clarification here. Should I care about what Jan says or not?

    • Jan Heine April 13, 2019 at 11:13 am #

      Stans No Tubes has been pushing their own, proprietary standard, which has a larger ERD and shorter G height. This may work – I have older Stans rims on my Firefly without any trouble – but we should avoid having several standards that may or may not be compatible. The ETRTO standard actually is very new, and it provides a roadmap forward.

  13. Nelson Zornitta April 12, 2019 at 1:35 pm #

    Well, a doubt remains: if G height is 5.2 for tubeless, and for tubed 5.5 (until 17c) to 6.5 (18 – 25c), if I use a tubeless rim, and have a flat 100km from home, that the sealant can’t seal, I can’t safely get home with a tube??

    • Jan Heine April 13, 2019 at 11:17 am #

      Don’t worry about it. Our testing found that with a tube, you have a far greater margin of safety: If a rim works tubeless, it’ll work even better (i.e., have an even lower risk of blowoff) with a tube. That is why we recommend that, if you have hookless rims, just use tubes, and you’ll probably be fine.
      Most older rims have a G height in the 6.0-6.5 mm range. I suspect the ETRTO didn’t want to define a new standard that excluded many existing rims that work very well, so they defined the standard like that.

  14. Adamar April 12, 2019 at 6:37 pm #

    That’s a “no” to Boyd Jocasse wheels then. Seems like all of the carbon gravel wheels are coming out hookless. Including the Hunt ones recently reblogged on Insta 🙂 Kind of a bummer.

    • Jan Heine April 15, 2019 at 11:03 am #

      You can always use tubes, and you probably won’t run into trouble. Most of all, rim standards are being worked on right now for the ISO (International Standards Organization), so hopefully, we’ll soon have a standard that everybody adheres to.