Rumor: Upcoming ETRTO Spec to Limit Inner Rim Width to 23mm for 28mm Tires

On the latest The Placeholders Geek Warning Podcast they mentioned that the ETRTO has agreed upon a spec that will limit the internal rim width to 23mm for 28mm tires. If this does happen, then the following rims (I’m sure there are others, but these are the biggies) are out of spec:

Really interested to see what happens if this goes through :popcorn:

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Well, it would simply require for those companies to update their manuals and online information re: which tires should be used with those rims.

Will definitely be interesting to follow….I personally have no issues with the rumored regulation. Too many people are pushing the edge of what is safe when it comes to road tubeless, IMO.


Frustrating that this is changing with the seasons… just bought some 303s to use for cx but doing road duty right now with gp5k str… 28s caliper out to 30, so is it measured 28 or printed 28? Is this bc of failures or to prevent failures? Did this just make the latest crop of high end wheels obsolete? Enve, zipp and many others have gone to 25 internal. Zipp even markets the aero gains from 25 hookless with 28 tires. If there’s a problem, do companies admit they were wrong and replace wheels with the new standard or tell you tough shit, buy new ones?

At a time that the bike industry is hurting, this really doesn’t help anything…

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According to the pod, there have been no reported incidents that are driving this proposed change.

Also worth noting that ETRTO is not the bike industry, but an independent, European group that sets standards ( similar to ISO).

As I noted above, the proposed change will not make current wheels obsolete, but it will require suppliers to change what tires they recommend for their rims.

IF the changes are adopted…which has not happened (yet).


Correct, not the bike industry but an accepted standard across the board

I agree, there’s a lot of pushing the limits, but that’s gatta be partially due to there being no set standard. Recommendations change so often. Back to my use case, I’m a big dude at 210#…. I run about 68-70 psi on hookless. I’m just shy of the mythical 73psi max. Am I pushing the limits with a 28 tire? Current spec sheet says no… havnt lost a tire…yet…

Again, my tires are printed 28 but measure just shy of 30 aired up… do I go by 28 recs or 30? On mtb, I wouldn’t give a hoot. Every modern tire is approved for any modern rim and no one is running even close to max psi. Not the case on road and the recommendations aren’t always clear

Regulatory standards will always be inherently conservative. See tire clearance standards as an example.

I don’t think it would be as easy as just changing the marketing material, since Zipp wouldn’t have a road wheel for use by normal people (unless everyone starts going to 30mm+ for road) and the for Enve that would mean that the only “road” rims would be the 6.7 & 7.8 in the SES lineup

The 303s is 23mm internal and would still be officially compatible with 28s.

ETRTO standards are certainly not in any way mandatory for Enve and Zipp, at least in the home market. I wonder if they will have separate approved tire and rim recommendations for the EU and leave it at that. Assuming they feel their 25mm rims are fine with 28s.

Good to know! Not sure where I got 25 from?… in that case, yea 25 is crap, everyone should be on 23 like me! Haha

If / when this spec comes out, hopefully someone will say why. Plus I will be interested to see what Enve and Zipp do in reaction to this. Both with their existing lines (e.g., does Enve rename the existing 3.4 & 4.5 to “AR” versions for tires over 30mm?) as well as for any new products they introduce.

AFAIK there’s no mandate to follow ETRTO, certainly not in the US and apparently not even EU, beyond how to label tires and rims. In fact, the ETRTO standard was quite out of sync with what most people have been riding for more than a decade. As of 2020, the only ETRTO approved rim type for tubeless tires was hooked 17 mm internal width. Nothing else was approved.

So, ETRTO rules about matching certain tire and rim sizes is really just a guideline. Wheels almost never come with tires from the wheel manufacturer and of course anyone can swap tires at any time. So worst that happens is they change their official recommendation.

There’s no way in hell they exchange rims for people and it’s ridiculous to suggest they should. The changing of the very conservative ETRTO recommendations doesn’t change what is actually safe, just what one committee decided to say.


303S are 23mm internal. 303 Firecrest are 25mm internal.

So, 404 Firecrests are fine.


I can’t speak to the EU as I don’t know if it is mandatory or not.

Yeah, I don’t get it. I also have carbon rims with 25 mm internal width (3T Discus C45|32 LTD) and have been using them with 28 mm tires. Zero problems.

Do they just want to be doubly, triply sure that there is enough safety margin?

I have Enve SES 4.5 on order right now and I feel a bit unsettled now. Was planning to run 28mm tires with these wheels and given this change this might not be within ertro standards anymore.

Is there any reason I should change my order to the 6.7’s because they have a lower 23mm inner width? I am 74 kg / 163 pds if that matters.

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I think consensus is that there are no wide-spread problems. In fact, I haven’t heard of any problems. In your case, you have to add the proviso “with compatible tires”, but that’s just because Enve rims are hookless.

I have run 28 mm tires on my 25 mm (internally) wide rims for close to 2 years now with zero issues. I weigh pretty the same as you if that matters. Also, the depth of 45–50ish mm the AR4.5s have is really the goldilocks depth. My 3Ts have the same width and I don’t feel my wheels giving me unwanted steering input even in the strongest crosswinds. I reckon the Enves perform equally well in this respect. If I were you I wouldn’t change my order.


fwiw: I’d been running 353 NSWs with 28mm Conti’s (5000 S TR) and had a horrific blowout on a fast descent back in feb that nearly killed me. Pressure was 60 psi, sealant was topped up as you’ll see in the pictures. My local Specialized dealer couldn’t find anything wrong with the Conti’s (they were intact, no punctures, but had separated almost entirely from the rim) and since we had to send the ZIPPs back to them for crash replacement we’ll never know if something was amiss with the wheels. After the ETRTO update I told them I was no longer comfortable riding on them. Maybe dramatic but just not worth risking it. I’ve just bought Alpinist CLX II which are hooked to replace my 353s


Man! glad to hear youre ok! This is unfortunately the kind of thing I wanted to hear about…just not at your expense! I have a set of hookless wheels (zipp 303s) whos main job is cyclocross, but Im using them on the road currently. Riding a hookless rim kinda keeps your unfortunate crash on my mind. Havnt had any issues yet, but really hate thinking about it when im riding. It could certainly happen riding cyclocross, but Im doin like 14-15mph in the grass/dirt/mud, not a 35mph hill!

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