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

Alburquerque, Nuevo Mexico, Etats Unis d'Amerique, Orbis Terrarum

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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.