The ISO (int'l standards org) has crystal clear recommendations for inner 
rim width and tire width, but they're not regulations. A couple of years 
ago I posted them in some form somewhere--and we had an internal talk about 
them--and all of us here and tons of you there have had the brake-opening 
experience and the soft-tire mushy-around-corner experience with a narrow 
rim, but that kind of Technical Whinery never sticks. Sheldon's 
chart--thanks for posting it, Patrick--looks pretty close to the ISO 
numbers, and it wouldn't surprise anybody if that's where he got 'em. 
The SILVER/Techtro 559 brakes were designed to address the wider opening 
solution to a 35mm tire on a skinny rim. We specified that and the reach 
and arm shape---and they're much better for it. It would be neat if all 
sidepulls had something like that, but these days in the go-fast community, 
"wide" is 28mm, so there's no need.
The ATLAS rim at 25.4 outer and I forget inner, but it holds up to a 45 
pretty well--although it would violate ISO recommendations at that. The 
Velocity Cliff hanger is nice at 30mm outside. (I dig that it's the inside 
that matters for tire holding, and the outside for brake  opening, but I 
can't break out of my outer-only numbers.)
The Alex DM 24 rim, at 31.7 or 32mm, is great for 45 to 60 tires. Big 
difference in holding. Best big tire non super fatty rim out there, but 
hard to get in 650B/584. We haven on new CLEMS because we paid for the 
tooling to make them. If you read the John Black BLUG post, you might 
wonder where "tooling costs" become a factor, when it wasn't for 
Velocity--it's just a matter of where to cut the straight extrusion before 
rolling it into a hoop. But at ALEX, there must  have been something else 
going on, because we paid a few thousand for it...and now "own" the 
machinery that allows them to roll the 32mm rim into 650B rims. Blah blah 
blah...sorry 'bout that, but I like this rim-width kind of talk, too.

On Monday, November 28, 2016 at 10:32:11 PM UTC-8, Eric Karnes wrote:
> Hi all-
> Wanted to get your thoughts...
> I have a set of OpenPro rims on which I comfortably run 35mm tires on my 
> Hilsen. I'd like to go up to the max knobbies that the bike can run (I'm 
> leaning toward 40mm Clements MSOs). Have people had success running tires 
> this wide on OpenPros or would it be more prudent to invest in a new set of 
> rims?
> Thanks!
> Eric
> ps. If anyone has a spare set of 40-ish mm knobbies you are looking to 
> part with, lemme know!

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