Jan Heine on the myth that wide tires need wide rims

[fiamme red]

https://janheine.wordpress.com/2019/...eed-wide-rims/.

• Rim width doesn’t matter for supple tires. You can run our widest Rene Herse tires on relatively narrow rims with little discernible difference in how the tire feels and corners.
• Don’t use a rim that is too wide for your tires. The tire should be at least 20% wider than the rim.

[dddd]

It's true what he is quoted as saying there, but tire size (width and volume) is affected a bit by rim width, and aero rims typically need a certain width of tire to perform their aero magic.
Obviously he isn't referring to aero rims.

I do feel that wider rims somewhat help with lateral stiffness of the tire, and that wider rims can lower the air pressure threshold where tire instability begins to be an issue (typically at very low pressures).

[saab2000]

I can't speak to really wide bike tires but I definitely like what a wider rim (20mm or so internal width) does to a 23-25mm tire. Since I can't really imagine using anything more than a 25 or maybe a 28 for 'normal' paved road riding it's a bit moot.

Wide rims do indeed seem to make a different sidewall profile and keep the tire from squishing about side to side. But I suspect he's referring to much wider tires than I'm referencing here.

[Davist]

Nope, at least with relatively low pressure, which he also advises. Any mountain biker from the 90s can tell a story of a 2.1" tire rolling off a 19mm rim.. I can, and I ran about 50 psi at the time..

[marciero]

Originally Posted by dddd

...

I do feel that wider rims somewhat help with lateral stiffness of the tire, and that wider rims can lower the air pressure threshold where tire instability begins to be an issue (typically at very low pressures).

I’d agree with this. Jan mostly is addressing the fact that with supple casings, sidewall stiffness does not contribute to supporting the tire, so having the sidewall more vertical does not help things. This is true but does not address the floppiness/squirm in corners, about which he says only that he does not notice additional squirm in corners. But a tire on a wider rim is going to deflect less sideways during cornering at a given air pressure.

His description of tubulars as being “attached only at the very bottom” (so being more like a clinchers on narrow rim) is not true either since tubulars are glued all the way to the edge of the rim. Tubulars-especially those used by Tour racers he uses as an example, being much narrower to begin with, are attached to the rim over a much greater percentage of their width than 42+ tires are going to be.

[AngryScientist]

I enjoy and appreciate Jan's mythbuster series. As with all of them, you have to distill out the useful information and have an idea of what information is either wrong or needs to be dismissed, but they are all thought provoking and mostly grounded with some actual product testing evidence.

In this case, i think the takeaway is that yes you can run the fat tires on narrow rims. on this forum and around the scene lately, the question of "can i run this 35mm tire on my 19mm rims comes up a LOT lately, as most modern rims are wider than that. the truth is that we were all riding CX and touring tires on open pro rims for years with no problem.

the bottom line, and i think the real concept that Jan is pushing overall is to try things out and see how it goes for yourself, not just accept what you have read or been told. this is especially true with tire pressure and tire volume. what works best for me on my roads or Jan and his roads may not even be close to ideal for anyone else; gotta try and see!

[colker]

Originally Posted by Davist

Nope, at least with relatively low pressure, which he also advises. Any mountain biker from the 90s can tell a story of a 2.1" tire rolling off a 19mm rim.. I can, and I ran about 50 psi at the time..

Not here.

[Davist]

fair enough. amend to "many" seemed to be a thing in CO at the time where I was.

[Mikej]

Originally Posted by Davist

Nope, at least with relatively low pressure, which he also advises. Any mountain biker from the 90s can tell a story of a 2.1" tire rolling off a 19mm rim.. I can, and I ran about 50 psi at the time..

Ive never heard of anybody worrying about rolling an mtb tire at 55 psi. Also, I am not buying what the op linked to -

[Brian Smith]

Originally Posted by Davist

Any mountain biker from the 90s can tell a story of a 2.1" tire rolling off a 19mm rim.. I can, and I ran about 50 psi at the time..

Ha, yeah. Especially in the hands of someone who actually rides the bike instead of just hanging on.
The riders who had to have the sub-395g rims from Sun who then ventured into a dual slalom race as part of their race weekend...
It's amazing how quickly an innertube can double in diameter when released from it's thicker-skinned confines.

[dddd]

I believe that the design of the rim (the inside shape that controls how much bead slack can result if the bead gets pulled inward by the sidewall) has more to do with how easily a tire bead might become dislodged than the specific inside width of the rim.

Those early ME40 rims were hard to install or remove a tire from, so wouldn't "lose the bead" even if the tire folded over as the result of the pressure being overcome by the loading put on the tread.

But the Japanese narrow MTB rims, wider (i19 vs. i13mm) as they were, were much more-prone to bead dislodgement because they were typically made to facilitate an easier tire change.

So it seems important not to attribute bead-dislodgement incidents to rim width when the rim's internal shape may have played a much bigger role in beads coming out of the rim cavity while riding.

Even with the easy fit of my WCS CX tires on my old Open Pro rims, I've ridden a flat rear tire to the finish line more than once and never had one come loose despite cornering at the limit in a sliding fashion while sprinting. So it still takes some doing to make a tire come off the rim if the rim shape isn't almost literally designed to release a too-soft tire.

Point being that most of today's higher-performing rims are designed with only a minimum of bead slack depth so as to optimize the rim structure. So even an under-inflated tire coming off of the rim becomes a less-likely possibility.

The part of the article about the tire deflection through the rim-to-pavement "travel" range caught my critical eye when it was stated that the wider rim results in a regressive spring rate and thus an easier-to-collapse tire.
I question that since the narrower rim would appear to more easily intrude into the tire's volume and thus use up the critical travel range because of the same sort of regression of the spring rate of the inflated tire.

There also seems to be at least some advantage to the stiff sidewall's added damping when for example I run a 2.4" (67mm actual) downhill tire (rear only) on an i51mm rim while running just 21psi.
The more-damped cushioning when traversing larger-scale rocks and sharp bumps seems to add a degree of control that was lacking when I ran a same-sized but more-supple tire at it's higher minimum of needed pressure to prevent pinch-flatting.

So there are many angles to consider, though Jan makes the very good point that you can still get good performance from good, wide tires using old-style narrow rims. And a lot of us who have used wide tires on narrow rims already know this to be somewhat true, especially after we have acquainted ourselves with just what is the range of front and rear pressure that works well for our conditions.

I think that the newer style of rim using a thicker, non-hooked rim bead with wider, lower-pressure tires is what I call making real progress, since the promise of no pinch flats with tubeless rims might only be useful if the rim isn't damaged in the process (elite-level racing possibly excepted since the parts might be free and you might finish your race with your damaged rim still holding the air and the tire bead).

[spoonrobot]

The myth series is just advertorials. Jan can't do anything other than write marketing copy these days, especially now that he's given up the scientific testing portion of BQ.

[Mark McM]

Originally Posted by dddd

The part of the article about the tire deflection through the rim-to-pavement "travel" range caught my critical eye when it was stated that the wider rim results in a regressive spring rate and thus an easier-to-collapse tire.
I question that since the narrower rim would appear to more easily intrude into the tire's volume and thus use up the critical travel range because of the same sort of regression of the spring rate of the inflated tire.).

I question this too, and I think it is a wild supposition on Jan Heine's part. Contrary to common perception, the tire does not behave like an air spring, at least in the sense that 'traditional' air spring works by changes in the air pressure. When loaded and flattened against the road, there is no significant change in air pressure. Instead, loads are transferred by a tire by changes in the direction and magnitude of tension in the casing. I'd be interested in seeing actual data on changes in force/deflection as a tire loaded, for different combinations of tire/rim widths.

[hobbanero]

this series seems long on conjecture and short (as in no) actual science. Some of Jan's assertions contradict what engineers with backyard testing rigs are finding.

[El Chaba]

most of my wheels are tubulars, so I don't need to concern myself with clincher rim width fashions for the most part. I have a camping bike with clinchers that has had 32 mm tires on 20 mm rims and nothing has exploded.