so I was listening to the Marginal Gains podcast a few weeks ago and Josh’s prediction was that road bike tire widths will evolve to be in the 28-30 mm width. I also finally got a gravel bike and I was surprised by how narrow the internal rim width is (<20mm).
Most of my current road bike wheels are 21 mm internal width, with the exception being some Bontragers with a 19mm internal width. The widest road tire I run is a 700x25 GP 4000 and those look like lollipops on the Bontragers.
So some questions
Are road internal widths headed to 25mm to accommodate the 28-30mm tire and will gravel go even wider?
Does the narrow width adversely affect the cornering/stability/grip of a gravel tire or are the dynamics of this application totally different?
If gravel rims should really be wider what are my choices? So far about the only thing I find that fits that description is some aluminum HED rims at a 25mm internal width.
We used to ride mountain rims that were 22mm before everything got all gnar. If new gravel bikes are going after similar terrain as older mountain bikes, then wider rims aren’t necessarily a requirement for riding gravel. There are advantages to wider rims, sure, aerodynamics and tire profile, but I’m not sure it’s a necessity or even more than marginal difference.
As an aside, I love how road bikes are going through stuff (disc brakes, wide rims) mountain bikes sorted through 15 years go.
Road rims will have to handle 25-32 mm tires, so 19-21 mm internal should do the job. (Unless the bike is pitched at the “all road” category).
From Sheldon Brown:
If you use a very narrow tire on a wide rim, you risk pinch flats and rim damage from road hazards.
If you use a very wide tire on a narrow rim, you risk sidewall or rim failure. This combination causes very sloppy handling at low speeds.
19 mm internal should fit up to 42 mm gravel tires, which would fit many (most?) gravel applications. If you are looking to fit 48mm (or even 2.1’ MTB) tires, then you may want to look at a wider rim.
so I was listening to the Marginal Gains podcast a few weeks ago and Josh’s prediction was that road bike tire widths will evolve to be in the 28-30 mm width.
I think this is measured width. Basically we’re already there. A 25 on a 21 internal is nearly 30. Conti has resized their tires to reflect wider internals, but their 25 is still a bit over 28.
The width of the tires in itself is only a minor contributor to aero - the bigger problem is the rim/tire combination.
Following the rule of 105 (external rim width should be at least 105% the width of the tire), you need to be looking at an external rim width of 30mm+ to maintain aero for tires in the 28-30mm (measured) range. The problem is, there are only a handful of mid-depth wheel models currently out there that are this wide externally.
As noted in the opening statement from this thread, Josh Portner reckons the trade-off between lower rolling resistance and the minor weight and aero penalties (with appropriate wheels) will be 28-30mm, and he knows a lot more about this stuff than I do.
i don’t think a 25mm internal width is necessary for 28mm or 30mm road tires. but when you say “gravel”, that’s a broad topic. i reviewed the HED Eroica a few days ago on the front page. one of my comments was about the 25mm internal on this rim, and how much easier it is to mount 47mm to 56mm tires, which is what i ride for gravel when i ride 650b wheels (which is most of the time now). but that might not be gravel to you.
i ride a zipp 303 on my gravel bike when i ride 700c tires, and i put tires up to 38mm on that wheel, quite successfully. so, one can certainly ride 21mm inner diameter find up to 42mm or so. but this is just on what’s easy or hard to use; i’m not commenting on (for example) aerodynamics.
When you say mount easier are you saying tires go on easier or set a tubeless bead easier…or both?
I think every tire/rim combo is different… I had to bin a couple schwalbe tire levers today after getting on my WTB Cross Boss on my Enve 4.5AR wheels… They lasted me about a year and were well used but after today they were done for sure.
My tried and true method now is put a tube in first and set the bead… remove tube and put in tubeless valve inflate to seat the bead again… deflate add sealant and inflate. It works everytime. No need for soapy water or any of that biz.
When you say mount easier are you saying tires go on easier or set a tubeless bead easier…or both?
there’s more room to stick the tire onto the rim, before you air it up, when you’re mounting it with your hands. it’s easier to air up, to get it to bead up, and for it to pop up without having to put 100psi into it. i have a set of tires, i put them on a narrower rim, they wouldn’t go on straight. they’d air up, but they’d roll oblong. i put them on the HED Eroica, they go on perfect. fat tires just goes on easier with a 25mm inner diameter. for me. but part of that is having a nice inner well for the tire.
That’s quite interesting as I have the Vanquish and notice they pop a tire right on with say a 35mm, but I have struggled to get the bead popped on (even with a compressor) at 38+mm tire width. I have tried quite a lot of tires just for fitting to the bike (clearance) purposes. The Vanquish rim is extremely easy to work with otherwise as in the tires fit nice and “loose” as to service easily in the field. Contrast that to another wheel I’ve tried that’s nearly impossible to service in the field by hand. The tires simply fit too tight on that brand.
My solution for the Vanquish will be to try a 2nd wrap of tape for the bigger tires. If that doesn’t make that initial tubeless beat set easier then I guess I now know the solution. But it’s unlikely I’d be willing to sacrifice the aero loss of the Eroica…so…
I think my prediction was 30-32mm for road as that’s where we begin to see the tapering off of rolling benefits on paved surfaces… but the show is unscripted, so might have said 28-30!
At this point, all of the safety data and everything we have on rim/tire interface, etc tells us that things get dangerous as the bead approaches the designed tire width. Remember, some of the air pressure in the tire is pushing the bead into place and also pushing the lower part of the casing radially inward toward the rim. Under ETRTO the bead width was extremely conservative… largely because beads stretched and tolerances weren’t as tight as they are now, but technically by ETRTO, the narrowest tire you can put on a 21mm bead width rim is a 35mm tire. In our testing, you can make a 25mm tire blow off of a 21mm bead width rim much more easily than it will come off of a 19mm rim and I haven’t tried putting a 25tire on a 25 rim, but I know that a 21mm tire won’t safely hold on a 21mm rim.
As a whole, the industry is still arguing the details here, my recommendation would be at minimum use a tire that is 4-5mm wider on the sidewall than the bead width of the rim for safety reasons, especially if using hookless beads.
