anyone breaking the rim/tire width ratio from Sheldon and Rene Herse?

[Brent Eastman]

I just acquired a soma san marcos with mavic open pro rims, inner rim width of 15mm. 

I immediately put 40mm tires on it, and have been riding it for a few weeks as I dial in the build.

It has a cycle ops power meter rear hub, looks gross, so I was planning on rebuilding the rear wheel with a cuter hub, but then realized I was fully in violation of the acceptable range of tire width for this rim. Should I just get a different wheelset?

the rim widths recommended by rene herse and sheldon seem to be conservative at 15mm but then generous at 17mm, idk, is anyone cheating and getting away with it?

[Brent Eastman]

Here's the rim / tire safety chart. I just find it hard to believe a 48mm tire on 17mm rim is safe, but 40/15 is not?

[Ben Miller]

40 mm tyres on 15 mm inner rims all laced to a power meter hub?? I want to see a photo of that!

IDK, but I say if you can get a tyre seated on a rim, it doesn't really matter what the rim width is at the lower end. Though at low pressures and supple sidewalls you may have excessive tyre squirm when cornering. But if you like the handling of them currently I wouldn't lose sleep over it. Though I also don't know that I'd recommend rebuilding the rear wheel either. Maybe sell the off to a weight weenie and acquire a new wheel set??

[Garth]

I had to test this for myself, and I did a week ago. I have a Mavic MA2 13mm internal width wheel on hand, and I mounted a 35mm Marathon Racer tire on to the same 40 psi I ride on my road bike with Mavic A719 rims @19mm inner width. Yea sure, they mounted just fine, but glaringly apparent was the width, the lack of it. Only 30mm on the MA2, and it just looked all wrong as it was so skinny that the tread was rolling over the sides. It's 34mm on the A719 and the proper shape. While sure, on the MA2 it may be considered relatively "safe", but seeing how the tire wasn't capable of being shaped normally, I saw no point in it and no way I'd want to ride it.  Just because it can be put on a rim doesn't mean it's a good idea. I tried this as I too was contemplating some Mavic road rims that are all 15mm inner, but after this, no thanks. A 17mm minimum for me with 35mm-45mm tires. So for another road bike w/130mm rear spacing I bought a set of Mavic Aksium wheels that come with a 17/23mm inner/outer rim. Mavic is so behind the times in regards to making retail rims for sale that are in the 17mm range. It's been 15mm for up to 28mm tires, or 19mm for 28-47mm tires since the 90's, at least !

[Tony Lockhart]

Hey Brent, I've been using an Ultegra/Open Pro wheel set on my Leo since December, 2023 and haven't had any problems. I'm currently using 38mm Soma Shikoros (35mm actual width) on the bike (40 psi rear, 30 psi front, rider weight 210 lbs) and I haven't had any issues. I put a couple hundred miles on these wheels with some 42mm Shikoros and didn't have any issue, however those wider tires are on my Sam with Atlas rims. While I've heard from loads of people that this combination is not optimal, I haven't had issues....the Leo feels sprightly compared to the Sam.

[Zac]

I ran Rene Herse Bon Jon Pass (35mm) tires on an Open Pro wheelset for years. Occasionally in downhill turns with speed I would notice a little squishiness. I'm keeping them now as a backup wheelset, but would feel fine going back to that combination.

[Patrick Moore]

As I’ve said before, I rode 50 mm knobbies on 13 mm IW rims. When I had Co Cyclist (I think) build my first custom mountain bike rims back circa 1992, I chose Sun M14A rims, again, 13 mm IW. They worked fine over thousands of miles with the usual 2” knobbies of the day as long as you kept the pressure high enough. FWIW, the Suns are very light at 360-370 grams (I use them as road rims nowadays) but also very strong indeed. More recently I rode 76 mm tires on 19-21mm IW rims; again, no problems.

Upshot: a 40 mm tire on an Open Pro might break somebody’s rules but it will cause no problems,

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[Patrick Moore]

I forgot to add that back 35 years ago rim mfrs manufactured and marketed 13 mm IW rims — there was a whole slew of “semi-aero” very narrow 26” rims made by Sun and Trek among others — explicitly for offroad use on  2” mountain bike tires. No one gave this a second thought and I, assiduous reader of the cycling press, never read of any failures or recalls.

[Andy Beichler]

I'm running 40mm Gravel King Slicks on a set of Open Pros right now.  They measure about 39mm and I have had no problems. 

[J G]

Bruce Gordon Rock and Roads at 43c were ridden on Open Pros for many years.

Not an issue.

[Cormac O'Keeffe]

Hey,

I've been using 42mm tyres on a Mavic Open Pros for about 14 months and no problems so far. 

However, they made an odd 'squirmy' noise for the first couple of rides. Something I'd  never heard when riding on wih 25mn or 28mm tyres. Is this because they're (the 42mm) are too big?

[Patrick Moore]

I think that certain tires just make “squirmy” sounds under cornering pressure. The 51 mm (actual width on 27 mm IW rims) Soma Supple Vitesse SLs handled corners crisply and perfectly at 20 to 22 psi (<200 lb bike + rider + kit) but made squirming sounds, while 54 mm Thunderburts on the same rims at 17 do not make this noise; nor did smooth-tread 61 mm ultralight Big Ones at 17. 

Come to think of it, the 42 mm Naches Passes on another bike also make these sounds briefly and occasionally at normal pressures (30-35 f, 35-40 rear).

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[Patrick Moore]

The NPs are mounted on Sun Ringle EQ 21 rims which are about the same width as Open Pros; 21 mm OW.

[Nick Payne]

My touring bike that I keep in Europe has been running 37-38mm width tyres on Mavic MA2 13mm internal width rims for many years. I've ridden that setup across both the Alps and Pyrenees without any problem. And I believe that very early MTB rims in the 1980s were made by cutting down the same MA2 rims, and they had even wider tyres fitted.

Nick Payne

[Tyler Ryan]

Brenton, I had the same question a while ago. I am running 35mm tires on 14mm internal width rims with no problems on my Ram. The general consensus that I seemed to find online was that this is just what people did before wide rims were easily available. 

On Thursday, October 9, 2025 at 1:55:17 PM UTC-7 brenton...@gmail.com wrote:

[Frank Brose]

Worth a read.

https://www.renehersecycles.com/myth-18-wide-tires-need-wide-rims/?srsltid=AfmBOoq_ACj2uT6WoTTZqcuL1APl-38K750jNZ9Ildp-5MeKz6dhMK2P

Frank

[Brenton Eastman]

That article is what prompted me to start this thread, because they reference the ETRTO chart, and many of us (confirmed here) are  guilty of violating the suggested max widths. 

On Oct 21, 2025, at 4:00 PM, Frank Brose <fkb...@gmail.com> wrote:

Worth a read.

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[Frank Brose]

Oh I'm definetly guilty. A number of years back I was curious about the same thing and It just happened to be about the time this article came out. I didn't want to be restricted to tire size but I didn't want to rebuild or buy new wheels either. I had already done it without problems but I was curious as to why it wasn't or was okay,  I finally put it on the back burner and decided if something works roll with it. No pun intended.

Frank

[Chuck Walton]

I believe the main point of this chart is to set a maximum safe internal rim width per measured tire size. With tubeless tires and hookless rims you could potentially create a dangerous set up by running a 28mm tire on a rim any wider than 23mm internal for example. Even more so as tire pressure increases with system weight and temperature.

The opposite situation with wide tires on narrow rims would decrease tire pressure, so less chance of the tire blowing off. I suspect there is a point where a narrow rim would start to distort the tire beyond its intended design, potentially decreasing its performance.

Great thread, and I'm personally running 700x35 Bon Jon Pass tires on Sun ME14A rims on my Rambouillet. The ride is sublime.

Chuck (in Pittsburgh)