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Myth 18: Wide Tires Need Wide Rims

Our series of ‘Myths in Cycling’ continues with a look at rim width. It seems to make sense that wider tires should run on wider rims.

The idea is this: A wider rim makes a tire more U-shaped (left), rather than O-shaped (right) on a narrower rim. The sidewalls are more vertical, so they can better support the weight of the rider. This is said to make the tire flex less, so it corners more predictably.

When we first started experimenting with wider tires more than a decade ago, I was concerned: There weren’t any really wide rims available back then. I mentioned this to framebuilder Peter Weigle (above, in the center). His response surprised me: “I don’t think rim width matters. We used to race mountain bikes on narrow Mavic MA-2 road racing rims. I actually preferred how the bike handled with the narrow rims.” This came from the guy who won the cyclocross national championships on a mountain bike!

When I thought about what Peter said in the context of all-road bikes we were developing, it started to make sense. The extreme case of an O-shaped tire is a tubular: It’s perfectly round, and it touches the rim only at its very bottom.

And yet tubular tires are known for descending very well. Almost all pro racers in the Tour de France (above) ride on tubulars. If vertical tire sidewalls were essential for good handling, tubulars would have fallen out of favor long ago.

I realized that with supple tires, the sidewalls don’t really hold up the weight of bike and rider. It’s the air that supports the weight. And thus rim width doesn’t really matter. On my Firefly, I run 54 mm-wide Rene Herse Rat Trap Pass tires on 20 mm-wide (internal) rims without any problems (above). And the Firefly corners even better than a racing bike, because it has so much more rubber on the road. Like the pros, I never notice any squirm caused by the O-shaped tires.

When you look at the ETRTO chart for tire and rim compatibility, you can see that 54 mm tires on 20 mm rims are no problem. I could even go as low as 19 mm. (The values are internal widths in millimeters, and the ‘C’ stands for ‘crotchet’ rims.)

The chart shows that the real concern is at the opposite end of the spectrum: If the rim is too wide, tire pressure no longer pushes the bead strongly against the hook of the rim. This can cause the tire to blow off the rim. The ETRTO chart is quite conservative in this respect and recommends rims that are significantly narrower than the tires.

Together with other tire and rim manufacturers, Rene Herse Cycles is working on expanding the chart to include wider rims. In our experience, it’s fine to use wider rims as long as the internal width is at least 20% narrower than the tire. For my 54 mm Rat Trap Pass tires, this means that I can run them on rims somewhere between 19 and 40 mm wide. On wider rims, the tires will get a little wider, but even that doesn’t make a huge difference – we are talking maybe 2-3 mm.

What if you run stiffer tires? Would you want a ‘better’ match of tire and rim widths to take advantage of the sidewall stiffness? When I was at Paul Camp a few years ago, I got to ride a wonderful Steve Rex monstercross bike, shod with mountain bike tires (above). When I first rode the bike, the tires felt very harsh. I let out air until the bike began to float over the rough gravel in Paul’s parking lot. I loved riding the Steve Rex, and I pushed it harder and harder.

When we reached some really technical terrain, the front tire’s sidewall collapsed as the tire hit some rocks. It was very sudden, and more extreme than I had experienced when running supple tires at too-low pressures.

When Paul’s mechanic saw this, he checked my tires and shook his head: “You need to run about 30 psi in those tires!” Now 30 psi (2 bar) is more than I run in my Rat Trap Pass Extralights. Perhaps the mechanic was overestimating my weight, or adding a factor of safety, but it appears that when you ride really hard, tires with stiff sidewalls may need almost as much air as supple tires.

Relying on the tire sidewall for support has a disadvantage: Once the tire starts to flex, it bows outward (right). It goes from U-shaped to O-shaped. The more it bows, the easier it becomes to flex. Once it starts to collapse, it becomes less and less stiff, and there is little to stop it. This is called a ‘regressive’ spring rate. It explains why the collapse of the tire was so extreme.

Using air to support the bike results in a ‘linear’ spring rate. No matter how hard you push on the tire, the air pressure doesn’t change: It continues to push back with the same force. (In theory, the pressure goes up slightly as the tire deforms, but the tire’s volume is so large that this isn’t significant.)

Mountain bikers have found that the best shocks have ‘linear rate’ coil springs. ‘Progressive rate’ air springs are a second option for those who want to save weight (air weighs less than a coil spring). Nobody would ever suggest a regressive spring rate, yet that is what you get when you use the tire’s sidewall as a spring.

This suggests that you might even want to run stiff tires on narrow rims: The O-shaped tire will be easier to flex and thus more comfortable. Without the tire ‘standing’ on its sidewall, you’ll have to run a little higher tire pressure, but then you don’t have to worry as much about the tire collapsing. When Peter Weigle mentioned that he preferred the ride of wide mountain bike tires on narrow rims, I believe he was talking about this.

With a supple tire, this effect is magnified: With mostly air holding up the bike, the spring rate is very linear, and you can run a lower total spring rate – less stiffness of tire and air combined. That means you get a tire that absorbs shocks better and is more comfortable. And because the supple casing absorbs less energy as it flexes, it’s faster, too.

What this means in the real world:

  • Rim width doesn’t matter for supple tires. You can run our widest Rene Herse tires on relatively narrow rims or on wide rims. There will be little or no discernible difference in how the tires feel and corner.
  • Don’t use a rim that is too wide for your tires. The tire should be at least 20% wider than the rim.
  • Using the tire sidewalls to hold up the rider results in a regressive spring rate. This can result in the tire collapsing suddenly.

Further reading:

58 Responses to Myth 18: Wide Tires Need Wide Rims

  1. samsavvas June 26, 2019 at 6:53 am #

    Jan, should your 2nd-to-last sentence not be the other way around? “The rim should be 20% wider than the tire.”

    • Jan Heine June 26, 2019 at 7:47 am #

      Yes! Thank you to all who pointed this out. It’s fixed!

  2. Franklin Miller June 26, 2019 at 7:20 am #

    This seems to explain what I found to be true with my Rat Trap tires on my Crust Romanceur (a bike designed to run Rat Trap Pass tires). I built it up with some nice light rims that were 19mm internal width and it rode great. I was then told that I needed much wider rims for those tires to be safe. Velocity Duallies were recommended. I built up a set of these and they completely changed the feel of the bike for the worse. The bike felt heavy and the handling sluggish. After a few rides I went back to my original rims and things have been great since.

  3. Getskied June 26, 2019 at 8:05 am #

    With a wider rim and the same tire run at the same pressure, one would get better aerodynamics and to some extent a decreased wheel/tire diameter, right?

    • Jan Heine June 26, 2019 at 8:11 am #

      All the measurements that showed improved aerodynamics apparently were with relatively narrow tires (up to 35 mm) and a smooth transition from rim to tire. With really wide tires, you can’t make the rim that wide… In any case, the effect appears to be really small – when we tested tire performance, we used the same (aero) rims for all tire widths, and we didn’t see any difference based on how well tire and rim width were matched.

      • Getskied June 26, 2019 at 8:22 am #

        Good to know. My current riding situation is such that I do a lot of mixed pavement/well-maintained gravel rides. I have mixed it up between Barlow Pass, Stampede Pass and Bon Jon Pass tires over the years (Bon Jons being used in 2019). It seems like in my case because I’m running “narrower” tires that the aero benefits could be more legitimate with a wider rim – which is not a reason in itself to upgrade from my stock gravel bike wheels but perhaps one among multiple. 🙂

  4. Gert June 26, 2019 at 8:41 am #

    Dear Jan,
    Please see here: https://torstenfrank.wordpress.com/2019/03/18/der-optimale-reifen-fur-rennrad-langstrecke-ultracycling-events-und-bikepacking-rennen/
    What is about aerodynamic aspects? Or is the writer wrong? I am sure you can read the German blog …

    • Jan Heine June 26, 2019 at 9:09 am #

      There have been wind tunnel tests that indicate a good transition from tire to rim is helpful, especially in crosswinds. It’s a small effect, just like the gains you get from running narrower handlebars or well-designed fenders. On the road, I doubt you’ll notice a real difference.

      In a long event like the TCR that the link mentions, I suspect the comfort benefits of wider tires far outweigh the aero benefits of a well-matched tire/rim combination. Short stops are key in events where the clock continues to tick regardless of whether you’re riding or not.

  5. David Haimson June 26, 2019 at 8:47 am #

    You say, “The tire should be 20% wider than the rim.” Don’t you mean, “at least 20% wider”? You’re successfully running 54mm tires on 20mm rims, 170% wider! Are there any limits?

    • Jan Heine June 26, 2019 at 8:57 am #

      You are right – I changed the text. I am sure there are limits – the ETRTO chart shows combinations that have been tested and found safe.

  6. Eric Langley June 26, 2019 at 8:52 am #

    I’ve noticed that going from a wider rim to a narrower rim results in narrower tire width, as measured by my non-scientific garage calipers.
    Is this something you’ve found, and are there performance/safety tradeoffs between having a narrower or wider tire tread on the ground even if the volume of air within the tire remains the same? (I presume air volume is the same, regardless of rim width)

    • Jan Heine June 26, 2019 at 9:11 am #

      Good tires are designed to have enough tread on the road with all rim widths. Conceivably, you could expose more a tad more tire sidewall when going to wider rims, leaving the tire less protected against sidewall cuts, but I doubt it’s significant.

  7. Jim Kukula June 26, 2019 at 8:58 am #

    Another factor with wide tires and narrow rims: the casing tension is pulling the rim apart more. Casing tension is greater with wider tires. It’s possible for a tire to pull a rim apart. Mostly the pressure for a tire decreases with width more rapidly than the casing tension increases, so the more outward angle of the tension won’t be a problem. But for a bike carrying a large weight, whether a big rider or camping gear or groceries etc., tire pressure needs to be high enough to support the weight, which can make wide tires on narrow rims risky.

    • Jan Heine June 26, 2019 at 9:16 am #

      That is an issue with carbon rims, and they usually have different maximum pressure ratings based on the tire width. In some cases, the maximum pressure really isn’t enough for loaded bikes. Most aluminum rims are strong enough that the maximum pressure of the tire becomes the limiting factor.

  8. John Stamstad June 26, 2019 at 9:03 am #

    Great article Jan. I totally agree with you based on my riding experiences.

  9. jasonmiles31 June 26, 2019 at 9:32 am #

    In my MTB riding, wider rims with larger tires helps prevent tire roll and burping of tubeless tires. You might not see these problems with tires 54mm wide but that is because your pressures are still likely higher than 25 psi. When your tires are around 66mm wide and larger you might start approaching 20 psi for some rides. In these cases wider rims make a big improvement.

    • Jan Heine June 26, 2019 at 9:34 am #

      You are right, our experience is mostly with supple all-road tires. That said, last weekend, I just rode 400 miles on gravel and single track on the Firefly, with the 54 mm tires at 15 psi – yes, the roads were rough! I had no issues, no burping, despite taking the bike and tires to the very limit many times on ultra-fast descents, washboard, giant potholes…

  10. Morten Reippuert June 26, 2019 at 9:37 am #

    Thx, im sick and tired of reading ‘the gospel’ of ‘wide rims’ for road tires – only advatage is IMHO arodymanics. ’round’ ballon shaped clincher tires just rides nicer and

    My trusted Mavic Open Pro Ceramic clincher rims mounted with 300TPI Chalange Parix-Roubaix’s baloons up at 29.3mm on the ‘narrow’ inner whith of 14.5mm. With latex tubes that wheelset descents like on rails compared to if i mounted with even more subtle but narrower 25mm Veloflex clinchers meassureing 25mm.
    My wheelset / tire of choise is a Campagnolo V-profile tubular rim with 28mm Vittoria Corsa G’s, meassuring 28.6mm – cornering and handling etc is just a tiny bit nicer than the open pro’s with Challenge/latex – however the tubular rims, tubular tires are about 100g lighter pr wheel – both rims laced with 32x Sapim Laser’s on Record hubs.
    My 3rd road wheelset is Reynolds 46/66 tubulars with 25mm Continental Competition’s, theyr are even lighter at way faster duer to the aerodymamic advantage but the narrower tires with butyl tubes does not corner as nice as the v-profile/Corsa combo – OR the Open Pro/Challange combo.

    (+ i have disc tubless wheels with 19mm inner profile for 35mm Bon John’s and 43mm GK’s – but the TI disc frame is nowhere near as nice as my TI road frame or my vintage steel road Koga-Miyata).

  11. Max Stevens June 26, 2019 at 9:50 am #

    Interesting article! You talk about the calculation needed at the upper end of rim width for wide tires (tire should be 20% wider then rim) but what about at the lower end? Does the rim need to be at minimum x% of the tire width?

    I have a set of wheels built up that have 14mm internal width – what’s the maximum width tires that I could run? Is it unlimited?

    • Jan Heine June 26, 2019 at 10:58 am #

      Check the ETRTO chart for the minimum rim width that is advisable.

      • Stuart Fogg June 26, 2019 at 11:20 am #

        Both Mavic and DT-Swiss have recently published charts with tire width, rim with, and pressure. For a given tire these generally allow wider rims than the ETRTO charts.

  12. theramblebeacon June 26, 2019 at 10:06 am #

    This is a really interesting topic about which I’ve thought a lot, so it’s cool to see you address it. I agree with what you wrote, and having worked for a company for years that is all about wide rims, I’ve had the opportunity to experiment with them a lot. I found that wide rims were fine as long as you rode in a straight line, but as soon as you went to corner, things go worse. In rough stuff, you’d hit the rim easily, and you’d feel the sidewall fold suddenly; on smooth stuff, you’d have that odd sensation of the sidewall folding instead of flexing the way it would with a narrower rim. Of course it’s true that at a point you’ll peel the tire off the rim under hard cornering with a narrower rim, but I’ve found that because the rim compresses into the tire more linearly with a narrower rim, you’re able to ride a slightly higher pressure to get around burping while maintaining the benefits of low pressure. I’ve tended to find myself having to run such low pressures on wide rims to get cush that I pull tires off a lot, and my rims end up full of dents! Anyway, interesting topic that I could go on about for ages. Mostly just wanted to say nicely done!

  13. Mackenzy June 26, 2019 at 10:24 am #

    I just built up a set of Mavic xc717 disc wheels with the intention of running Rat Trap’s for a lightweight 26″ wheel set. The rims externally are 23mm, but it’s hard to find specs of the inner width as they are no longer made. If I recall they have a 17-18mm inner diameter. You mention “as low as 19” – would it be fine to run RTP’s with the narrower xc717’s?

    • Jan Heine June 26, 2019 at 10:59 am #

      The rims on the Firefly are 24 mm external and just over 20 mm internal. Based on that, you should be fine with your 23 mm-wide rims.

    • steve June 27, 2019 at 5:29 pm #

      for a few months i have had Rat Trap Pass Extralight mounted on Mavic XC717 (non-disc) rims; these rims (disc or not) are 17mm inner width, and Mavic themselves recommend(ed) up to 2.1″ (53mm) tires:

      https://tech.mavic.com/tech-mavic/technical_manual/data/docs/products/2_102.pdf

      my RTPs measure 49.5-50mm on these rims (and by the way, are difficult to seat properly with inner tubes — over-inflating helps)

      on pavement i fairly often feel them squirm when cornering hard, especially when the surface has some irregularities that run in the direction of travel (such as a transition from concrete gutter to asphalt road surface); i am less aggressive than i used to be, so i haven’t discovered what happens when i push them harder, but they feel like they’ll roll over, and in traffic i have to suppress my instinct for a course correction; to be clear, they have not rolled over on me or caused an accident; it may be i’m just not used to this feeling; i rode mountain bikes with stiff knobby tires very hard on streets for many years and they never felt like this, but i was probably at about 45-60psi vs 30-35 for the RTP

      i have also had 50mm Schwalbe Big Ben tires on 700c Mavic Open Pros (15mm internal); regardless of their much stiffer sidewall, these squirmed too, and it was subjectively scarier … RTP is a much better performing tire overall

      since 20mm is only moderately wider than 17mm, and since i’m sure Jan rides harder than me, i raised an eyebrow at his claim of no squirm at all with the Rat Trap Pass; i would not choose the 717s again for this tire

      • Jan Heine June 29, 2019 at 3:42 pm #

        It’s hard to say what is going on, but 17 mm is outside the ETRTO recommendation for a 54 mm tire… There may be a reason for that.

  14. Jim G June 26, 2019 at 10:49 am #

    Back in 1984, Keith Bontrager, used to cut and re-roll 700C Mavic MA-2 rims down to fit 26″ MTB tires, because he wanted lighter wheels. See https://en.wikipedia.org/wiki/Keith_Bontrager#Bicycles

    • Jan Heine June 26, 2019 at 11:00 am #

      Yes, those are the MA-2s that Peter Weigle used to race on…

    • Ray Varella June 26, 2019 at 9:34 pm #

      MA-40s as well. I had a pair from him.

      I still have a few MA2s stashed in that size.
      Maybe a 26” wheel allroader is in my future.

  15. Patrick June 26, 2019 at 10:57 am #

    Finally, someone talking about running wider rims on relatively narrow tires. I searched up and down and I could not find whether putting a 32c tire on a 25.5 mm internal rim was a safe thing to do. Looks like it’s right at the limit of that 20% reduction from tire width you mention. Thanks for putting your research (and tires) into the weeds.

  16. Stuart Fogg June 26, 2019 at 11:28 am #

    In a tire with supple sidewalls isn’t it actually sidewall tension which supports the weight (as well as lateral forced from cornering and tangential forces from pedaling and braking)? Since the sidewall tension comes from air pressure they’re closely related, but the effects of sidewall tension depend on the angle where the sidewall meets the rim.

  17. fhfr436 June 26, 2019 at 11:37 am #

    Great article. I have been riding (seriously anyway) since 1988 and remember the “narrow rim revolution” started by Keith Bontrager. Hearing the more recent cries and accolades for wider rims, using the SAME justification from the 1990s, but for opposite effect, has made me chuckle. The comparison with O-shaped tubular tires is perfect.

  18. Stuart Fogg June 26, 2019 at 11:43 am #

    Some off-road tires have different tread patterns on the sides than in the center and have a fairly narrow range of recommended rim widths to make the tread function as intended. My take is to listen to what the tire maker says – if you’re riding Rene Herse then listen to Jan.

  19. Weston June 26, 2019 at 11:46 am #

    Thanks for the great article! Was most of the testing process done with tubeless setups? Do you think tube/tubeless makes any difference in this scenario?

    • Jan Heine June 26, 2019 at 11:51 am #

      We tested both with tubes and tubeless, and we found little difference in how the tire handles on different-width rims.

  20. Paul June 26, 2019 at 12:28 pm #

    “Mountain bikers have found that the best shocks have ‘linear rate’ coil springs. ‘Progressive rate’ air springs are a second option for those who want to save weight (air weighs less than a coil spring).”

    This demonstrates your point well, but it is a bit of an over simplification.

    The linearity of coils are great for small bump sensitivity, but once you get into bigger hits and drops (i.e., further into the travel), some degree of progressiveness is needed to prevent harsh bottom outs. This is evident from the numerous fork and shock tuning guides describing situations when adding volume reducers to increase the progressiveness of the air springs of a fork or shock could be beneficial. Very progressive rear ends can feel “bottomless” like best powder day you’ve ever skied. It’s pretty cool.

    Of course all of this varies based on the weight, skill, riding style, and personal preferences of the rider, as well as the terrain and even the design of the rear linkage in the case of a full suspension bikes (this will include thew fork as well if the new linkage-based front fork designs catch on).

  21. Jacob Musha June 26, 2019 at 12:31 pm #

    It’s nice to see this analysis. I was worried that my 21mm outer-width rims are too narrow for the 51mm Rat Trap Pass tires. But after two years and no issues, I must not be missing much…

    I wonder how this scales up to plus/fat tires in the 70-120mm range. For those tires, everyone seems to recommend using rims that are much closer to the tire’s width.

    • Mike M June 26, 2019 at 2:03 pm #

      I’ve been running RTPs on 23-25 mm rims for over two years now. I was thinking of going to wider rims around 29 mm when I need replacements, but I think I’ll stick with my current size. Two years of spirited riding on wide tires and narrow rims without issues is nothing to dismiss out of hand. Why mess with success?

      I too would be interested to see how things look when you get into the “fat” tire range. Extrapolating from the ETRTO chart, I’d say they’d recommend 23 mm rides right around 74 mm, and by 100 mm tires, you’d be looking at a minimum rim of 30-32 mm. Just a pure guess on my part, mind you; I haven’t looked to see if ETRTO itself has an expanded chart. It would be a sight to behold: a 3-4 inch tire held on a ~1.5 inch rim!

    • Craig Lloyd June 27, 2019 at 12:36 am #

      I wonder if, due to the extreme width of these plus/fat tyres they are made with more of a motorbike profile ie. lower sidewalls with a larger radius curve on the tread? Think of a performance car tyre but not flat on top. This would cut the weight of rubber involved and the overall wheel diameter for such a large width tyre. Because there is less sidewall the tyre can never approach that “O” cross section so the rim must go out wider to meet it.

      That’s my view of the physical set-up, but I have no clue about the how the pressures, forces or riding styles involved with fat bikes interact with this or how it would be different if they copied standard tyre shape. I watched a friend play/test a 3 inch plus-bike he had built up that had fairly thin sidewalls… I could see the sidewall crease under load when he did an endo in the carpark… it made me wonder about how it would react to high-speed cornering.

  22. Chris Kostman June 26, 2019 at 12:54 pm #

    I’m sorry, but with all due respect to both you and Peter Weigle, this is total bullshit. I remember very well when “we” went to Mavic MA-2 rims and I just about slid right off the mountain the first time I cornered hard on a mountain bike with skinny rims. The tyre just rolled / swayed WAY over to the side and I was riding on the sidewall. It was pure insanity and after one ride, I tossed those Mavic rims aside immediately. That ain’t no myth; that’s reality. I know you like being the iconoclast – and I relate completely; remember, I wrote “Mountain Bikes: Who Needs Them?” way back in late 1992 – but sometimes you go too far and this is a perfect example.

    • Jan Heine June 26, 2019 at 1:20 pm #

      I have to admit that I haven’t ridden 90s mountain bikes with the narrow MA-2 rims, so I cannot comment on your experience. Somehow Peter and others managed to win races on those narrow rims – they may have done something differently. I’ve often mentioned that mountain bikes aren’t my specialty – we’re about all-road bikes.

      In that context, I feel confident that what I wrote is correct and works well: I just came back from a 400-mile, 2-day ride on gravel roads and single track from Klamath Falls to Portland via Crater Lake. I was riding 54 mm tires on 20 mm rims, with no problems whatsoever. Whether it was on fast pavement or gravel, the wide tires cornered great, and there didn’t seem to be a drawback to the narrow rims.

      • Paul June 27, 2019 at 10:18 am #

        That’s impressive, but doesn’t really translate to the situations where mountain bikers in particular are moving towards wider rims. I’m thinking you should go ride Predator on Tiger Mountain in Issaquah (near you, IIRC) with narrow rims (20 mm, internal) and wide tires (2.5″) and report back.

        • Jan Heine June 27, 2019 at 11:20 am #

          This isn’t intended at all to apply to mountain bikes. I don’t purport to be an expert, but in the little time that I’ve spent mountain biking, I’ve come to realize that mountain bikes are very different from road bikes. At Rene Herse Cycles, we make parts and tires for all-road bikes, and we feel that, as the name implies, they are an extension of road bikes, not drop-bar mountain bikes.

  23. smashndash June 26, 2019 at 1:49 pm #

    Hey Jan, huge fan of your work. But for the first time, I think I don’t completely alisgn with your post.

    Suppose we have two setups: setup A is a 30mm nominal tires on a 15mm rim, measuring at 30mm. Setup B is a 25mm nominal tire on a 23mm rim (extreme, yes). Setup B measures out to 30mm.

    Setup A’s tire profile is relatively more narrow and tall. Wouldn’t that make it more likely to collapse than setup B? You claim setup A is like a tubular, but I think that’s inaccurate. A tubular tire sits deep with the V channel of the rim. When turning, this V shape provides lateral support. I’ve looked into whether prefer to, for example, use 21mm rims with 28mm tubulars, but many people prefer the lateral support of a 28mm rim with the same tire.

    Also, setup B is more aerodynamic than setup A while having a similar amount of grip and air volume.

    I could be wrong, but I’m putting my money where my mouth is. My next wheelset is a 23mm internal rim that I will run with a 25mm Pirelli P Zero, one of the most supple road tires out there. The above is just conjecture, but I’ll know for myself soon enough.

    • Jan Heine June 27, 2019 at 12:02 pm #

      Setup A’s tire profile is relatively more narrow and tall.

      I’m not sure this is the case. The circumference of the casing doesn’t change, so when you make the tire more O-shaped, it should become less tall. Haven’t measured it, because the effect is going to be very small.

      A tubular tire sits deep with the V channel of the rim.

      Tubular tires are always O-shaped. That is why they are more comfortable and absorb shocks better than clinchers. If tubulars were nestled inside the rim like a clincher, nobody would bother with the hassle of gluing tires to rims, but just run clinchers instead!

      However, you can get the ride of a tubular by just going a bit wider in a clincher. And with wide tires, the rim covers less of the tire’s circumference, so the difference between tubulars and clinchers becomes less pronounced. That is why we don’t make 54 mm tubulars – although the thought has crossed our minds.

  24. Sam Atkinson June 26, 2019 at 2:25 pm #

    >”The idea is this: A wider rim makes a tire more U-shaped (left), rather than O-shaped (right) on a narrower rim. The sidewalls are more vertical, so they can better support the weight of the rider. This is said to make the tire flex less, so it corners more predictably.”

    I’m not sure I’ve seen that argument. The claim that tends to come up is that the wider bead placement forms a rotationally-stiffer brace to prevent the tire from buckling to the side when the contact patch is subjected to shear forces.

  25. Thomas June 26, 2019 at 2:39 pm #

    As a wide-tire aside, any chance the Rat Trap Pass tires may get the knobby tread of RH’s other offerings?

  26. John C. Wilson June 27, 2019 at 5:37 am #

    The micro quantities of MA2 and Super Champ rims cut down and re-rolled from 40 hole 622 to 36 hole 559 get all the attention. The cool kids had those. The cool kids are still completely in charge of the discussion. Meanwhile Trek was using very same extrusion used on their Iso road rims to make Iso mountain rims and selling them in very large quantity. Araya was selling mountain rims which were same extrusion as skinny road rims and selling those in very large quantity. There were riders using the older heavier and wider Araya 7X, there were other rims with a bit of width. Early MTB had lots of problems. The riders were ready long before the machines were. Where I was riding the supposed problem of wide tires on skinny rims did not rise to level of consciousness. When MTB went to uniformly wide most of us thought it was because wide rims are stronger.

  27. Conrad June 27, 2019 at 9:08 am #

    I havent gotten around to purchasing a modern mountain bike. So I am still riding a 26 hardtail with narrow (by modern standards) rims. I never switched to wider rims because why fix something if it isnt broken. It is true that with a typical (stiff) mountain bike tire you have to have enough pressure in there to avoid collapsing the tire. A more supple tire like the rat trap is much more predictable when you begin to collapse the tire while cornering. We are all sounding like a broken record here, but I could really use a set of knobby rat traps!!!

  28. Kurt Sperry June 27, 2019 at 11:47 am #

    Lessons forgotten have to be relearned. As has been noted, in the late pre-boingy fork MTB era, wide MTB tires were commonly mounted on narrow, cut-down MA-series rims and it worked great. And it worked best for me with Ritchey WCS-series tires with what I thought were almost scary-looking thin sidewalls/casings. There was more chance of sidewall damage off-road, but it was worth it for the feel.

    A high-end lightweight Prestige-tubed MTB from that era in fact is very nearly what the better gravel cum all-road bikes, knobs aside, are currently slowly re-inventing. I’m guessing that nice but anonymous Prestige Taiwanese-made frames are out there pretty cheap and that would likely be a very logical starting point for a high performance, low budget DIY all-road bike.

    Just like modern randonneur bike makers had to look backwards to benefit from the body empirical, experiential data that the French had worked so hard to obtain decades earlier, so it may be that there are things to be learned looking back to the late eighties/early nineties MTB scene. It was a period where — again — nearly every conceivable idea was built and tried out in full public view in serious sporting competition.

    • steve June 27, 2019 at 6:15 pm #

      i’ve been a big fan of older MTB frames configured as street bikes (which i see as something closer to “all road” than “road bike”); as you note, there a lot of great old frames with good geometry, and they can be very inexpensive project bikes; i have had several of late 80s/early 90s steel frames, but currently i’m riding a later Merlin Echo (ti frame, Moots-style soft tail) with Rat Trap Pass tires, rigid fork and Jones Bars; set up 1×10 with reliable midrange components it’s about 20 lbs. and except that i don’t think i really need the soft tail, i think it’s the bike i’ll ride into the hereafter

  29. Rodd Heino June 27, 2019 at 12:23 pm #

    Yep. I’ve been running the Barlow Pass in EL casing on Ksyrium’s from 2007, 13mm interior width at pressure down around 30 psi with no issues… I weigh around 165 lbs

  30. Stewart L June 28, 2019 at 12:32 pm #

    Lot’s of little mistakes and one big one, which is: A tire with sidewalls that is supple (technically both flexible/compliant and inelastic) will provide — except in rare circumstances — no more than de minimis support to the rims.

    To show this takes far more than 200 words and lots of physics/engineering and math. I should be able to put something together within a week and I will email to customerservice@renehersecycles.com. If you are nerdy enough, you will enjoy it.

    • Jan Heine June 29, 2019 at 3:44 pm #

      My point exactly: With supple tires, whether you run wide or narrow rims makes little difference, because the sidewalls don’t really hold up the bike. That is why supple tires run higher pressures (yet they are more comfortable).

  31. Stuart Fogg June 28, 2019 at 7:19 pm #

    This is more than I can do for myself, but I’d like to see the 55-622 Antelope Hill tested with 4 very different rims:
    * 19mm: Pretty standard road size, about the ETRTO minimum for a 55mm tire.
    * 23mm: Wide allroad or narrow mountain applications.
    * 30mm: Wide mountain applications, same ratio as a 28mm road tire on a 15mm rim.
    * 40mm: Plus mountain applications, same ratio as a 28mm road tire on a 20mm rim.
    I’m particularly interested in steering response and crosswind sensitivity at low pressures.

  32. E Borgnes June 29, 2019 at 10:46 am #

    I buy your thoughts on rim internal diameter (ID) making the tire more round instead of U shaped for better ride quality, etc. What I’m stuck on is that doesn’t rim external diameter (ED) matter just as much if not more than ID? When I read or hear the argument that a wider rim “supports” the tire better, I think of the rim ED, not the rim ID.

    Think of the racing tubular wheel/tire analogy: The tubulars are glued onto a shallow semicircular groove. The outer margin of the glue acts somewhat like the ID of a clincher rim, and since we apply glue all the way to the edge of the rim, the tubular ID and ED are essentially the same. And, a nice riding tubular rim is fairly wide relative to the width of the tire. So, I’m stuck on the idea that there seem to be benefits for both a wider ED (within reason) and a narrower ID….

    Would a wider rim hook set inside a wider ED rim be more optimal?

    • Tim Cupery June 29, 2019 at 5:32 pm #

      The difference between external and internal diameter is usually very similar, as you need a set amount of aluminum for brake track and a pretty standard thickness of the rim hook. So there’s not much variation of ED relative to ID, so no reason to need to talk about two dimensions separately.

  33. randonneur_indub June 29, 2019 at 8:01 pm #

    A combination of flexible tires and wide rims can lower air pressure. Smooth cornering, good ride, worse on narrow rims.