Road tire for gravel rim... help!

My wife signed up to do a century ride on her 2015 Specialized Diverge gravel bike. The century ride is entirely road, so I wanted to get her some faster road tires. The rims state ETRTO 21 (21mm internal rim width). From what I have researched, the narrowest approved tire for that rim would be a 35mm tire. It also appears that finding a 35mm road tire is near impossible. The bike originally came with a tire listed at 30/32. So, can she run a 30mm tire on those rims? Is there a 35mm tire that someone would recommend? The rims are crochet type and would be set up tubeless.

That min tire size seems off. On my 20mm internal width rims I’m running 28mm tires, and previously I ran 25mm tires. Where are you seeing the min tire size requirement?

Same info from multiple sources. Here is an example from Schwalbe.


Hookless rims of the same width can support narrower tires, but her rims are not hookless.

Really? I think lots of proper road tires are available in 34+ mm.

Lastly, regarding tire width: I don’t think what you researched is correct. I have 3T Discus 45|32, which have a 25 mm internal rim width, much wider than your rims. I have been using 28 mm tires for 2 years with zero issues. The tire width is officially supported by 3T. (They claim the rims have been aerodynamically optimized for 28 mm tires.)

1 Like

ERTO standards are just that… Standards. Things may work outside of that. This chart from Schwalbe says 28s on 21mm rims are good to go.

I run 28s on 21mm rims and the rim manufacturer states that it’s fine.

Anecdotally I agree. I’d even run 25s but that’s really getting close to the extreme.

1 Like

@DingleTower That chart opens up a ton of options and backs up the idea that the standard seems a bit off.

@OreoCookie I found some options that exist in theory, but I’m trying to find something actually available to purchase. Anything wider than 30mm seems to exist only in catalogs. :grinning:

1 Like

The recommendations are way too conservative. I own 3T Discus 45|32 wheels, which are 25 mm wide (internal). 3T states that the rims are aerodynamically optimized for 28–32 mm tires, but support wider tires, obviously. I have been running them with 28 mm tires for 2 years with zero issues. (These are hooked rims.)

In practice, 21 mm should work flawlessly with 25 mm tires. Since 25 mm is probably the narrowest tire you want to run these days, basically, you’ll be fine. 30–34 mm slicks would be very nice and still run fast. 30 mm might run just as fast as narrower tires at equivalent pressures.

1 Like

Rene Herse Bon Jon Pass.


You can order the Schwalbe’s or the Panaracers from Amazon(.com) right now. The 35 mm Gravelkings seem backordered, but you can have the 32 mms in 2 days or the 38 mms in a week. I’m sure they are also available on the other Amazons. Alternatively, you could also try and all the other usual suspects.

All my road wheels have 21mm internal width. E.g. old Roval CLX was optimized to 25mm if i recall. The new CLX II is stated to be optimized to 26mm turbo tires.

On other wheels I used mainly for CX, worked with 25mm road tires but due the profile they looked extreme. So I opted 28mm tires for those wheels instead. That made better combo than 25mm tires.

So my two cents, most likely you can find plenty of road tires to work with those wheels. But exactly what is the best width depends on the wheels and your preference.

Exactly this. In fact, I don’t think I’d buy a road rim narrower than 21mm these days.


I assume she doesn’t run aero wheels so I’d go for something wide like Conti 5000 TR S in 32 or if you wanna splurge a RH Barlow Pass Extralight in 38mm. You can take either tyre on light gravel/allroad rides just fine. Make sure she rides at the appropriate pressure: SILCA Professional Tire Pressure Calculator

Everything above a 25c Tyre should be fine on those rims, A 30 or 32c should do fine and there are a lot of options to run like the Conti GP5000, Pirelli P Zero, Schwalbe One, Vittoria Corsas etc… The differences between those top range tyres are relatively small especially if you don’t care for marginal Performance gains, so get the one that has the best price / availability. I would say the 2nd tier tires from all those brands are good enough if you’re not racing.


Also look at Hutchinson tubeless tyres - had many of these tyres in various widths over the years. Fitting tubeless was a doddle every time and they lasted well. I’ve got Fusion 5 in a 30mm on the best bike, Fusion Storm on the winter wheels and before those I ran Sectors in a 32mm width.
I’m sure you’ll find something just decide and go with what’s available.
There is that other longer thread about road tubeless options too… that may have somethhng of use for you. :+1:
Edit and even SK Gravel Kings in a 38 are still pretty good on the road. I’m always setting pb’s on tarmac sections with those on between the trail bits.

1 Like

My wheels are 31 external and 25 internal and they were perfect with the GP5000 S TR in a 32 but they are hookless so my experience may not apply.

I will say it was hard to find those tires online, was able to find them at a different LBS.

28mm or 32mm road tires will be fine on those wheels. And many decent tires are available in those widths. I’m partial to Conti and Specialized, but there are other options.