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What characteristics of a clincher rim affect ease of mounting tyres?

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What characteristics of a clincher rim affect ease of mounting tyres?

Old 08-02-17, 10:30 PM
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atwl77
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What characteristics of a clincher rim affect ease of mounting tyres?

Hi, curious about the question in the title. I've tried searching for specifics on Google but haven't come across anything definitive (or maybe my Google-fu is simply too weak), but most that I have come across is simply tubeless-ready rims are harder to fit than non-tubeless, but without going into specifics.


So how do the different rim characteristics make it easier or more difficult to mount a tyre -- especially that very last bit of bead that usually requires a lot of strength and cursing -- to get over? The rim depth? Width? Some particular shape of the rim, presence of centre channel?


Thanks in advance!
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Old 08-02-17, 10:58 PM
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Originally Posted by atwl77 View Post
Hi, curious about the question in the title. I've tried searching for specifics on Google but haven't come across anything definitive (or maybe my Google-fu is simply too weak), but most that I have come across is simply tubeless-ready rims are harder to fit than non-tubeless, but without going into specifics.


So how do the different rim characteristics make it easier or more difficult to mount a tyre -- especially that very last bit of bead that usually requires a lot of strength and cursing -- to get over? The rim depth? Width? Some particular shape of the rim, presence of centre channel?


Thanks in advance!
Generally, high side walls with a deep center channel make it easy to seat. The beads drop into the center channel, giving you plenty of slop, until the tube pushes the tire upward and outward against the bead hooks.

To make tubeless tires seal well, they typically have relatively short side-walls, and many have a shallow center depression also. This means there's no where for the tire to drop into to give you clearance needed on the opposite side. Additionally, tubeless beads are frequently stronger than a standard clincher and have less potential stretch. The combination can make for a real beast to get mounted.
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Old 08-03-17, 05:20 AM
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Thanks.


What about the width of the rim -- does it make any difference at all?
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Old 08-03-17, 05:36 AM
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Width should not make a significant difference, except for very narrow rims. Mounting technique actually has a large impact. Especially important is finishing the 2nd bead near the valve stem, rather than across on the opposite side of the wheel.
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Old 08-03-17, 06:10 AM
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The way I read your post, @atwl77, you're talking about the effort it takes to physically push the second bead up over that last part of the rim sidewall, right? I think, in many cases, it's simply the physical diameter of the sidewall's top edge. We know that for any given rim diameter (622mm for example), the bead seat diameter should be somewhat predictable, but the height of the sidewall of the rim above that actual bead seat diameter can vary a little I imagine. Probably not a lot, but it also wouldn't take a lot to have a big impact.

As an example, I own one set of rims that gives great difficulty mounting tires -- the Matrix Vapor rims on a '97 Trek. The width of the rim is more or less in line with other rims I own. But, every tire I've tried to mount on it proves incredibly difficult. And, by "mount", I mean getting the second bead physically over the sidewall. Seating the beads isn't the problem -- it's physically pushing the second bead up and over the sidewall. In contrast, the very same pair of tires mount to Bontrager AT-750s super easy. They just seem to slip over the wheel with seemingly little thumb effort. By the same person (me), using the same technique.

I've chalked this up to the actual outer diameter of the top lip of the sidewall. I never have measured the two wheels to see if there's a measurable difference. I might do that today, out of curiosity. If there is a difference, I suspect the Matrix Vapors have a slightly taller sidewall lip, or at least one with a slightly larger outer diameter than the AT-750s have.
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Old 08-03-17, 10:01 AM
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Originally Posted by hokiefyd View Post
The way I read your post, (edited out because apparently I can't even quote a link yet), you're talking about the effort it takes to physically push the second bead up over that last part of the rim sidewall, right?
Yes, that's exactly it. Would be interesting finding if your measurements agree with your observations.
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Old 08-03-17, 11:53 AM
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Many of the rims/wheels marketed as "tubeless ready" are notoriously hard to mount tires on.

In theory the tire should drop down into the valley, and be easy to mount, but at least with road rims, that isn't really true.

I don't think it is the height of the sidewall, although, it may be slightly different, but rather the placement of the bead seat in effect giving a shallow sidewall as mentioned above.
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Old 08-03-17, 12:14 PM
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There are also rim/tire combinations that are notoriously difficult to mount. I had Specialized Armadillos in 700 x 25 and older Matrix rims and getting that second bead on by hand would have made a nun swear. I'm now running Bontrager AW3 in the same size on Open Pro rims and even when new, the tires mount with only moderate effort. After they've been on the bike a while, they mount easily.

In my experience, kevlar bead folders mount more easily than wire bead tires.
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Old 08-03-17, 12:29 PM
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as in #2, Wolber Super Champion model 58 rims, were a single wall rim with a deep center well between square tube like bead seat shelves..

the drop center did aid tire mounting . these were a good rim in the 80's for touring wheels ..

wide MTB type tires tend to be easier to mount on the rims..

miss matching the ETRTO Standards on rim or tire bead circumference, can always create problems.





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Old 08-03-17, 01:14 PM
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Originally Posted by Myosmith View Post
In my experience, kevlar bead folders mount more easily than wire bead tires.
I tried three different tires on my Matrix Vapor rims, and the set that does have a folding bead was the easiest to mount -- they still required much more prying than they did on my AT-750s (I switched the tires from the 750s to the Vapors), but they were, indeed, easier to mount those than a couple pairs of wire bead tires I had.

Accurately measuring the diameter of the top of the sidewall of the rim will likely be difficult. I could dismount the tires and find the circumference by rolling the hoop, but I don't really care to do that, given how difficult it was to get the tires on the rims. I could try the string circumference method, but I don't think that'd be accurate either. The protrusion of the hub makes an accurate diameter difficult to achieve. I might be able to get a radius from the center of the top of the axle (both hubs use 100mm spacing), but any difference in rim width would affect that.

All I know is, these are "durn tough" to mount tires on! (They actually have a bit of a reputation for that.)
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Old 08-03-17, 02:00 PM
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As tough as it may be to mount tires on tubeless-ready rims, they are a welcome move toward making loosey-goosey "standards" more precise. Some of the issues facing tubeless tires are the same as those faced with the old non-hooked clincher rims -- a deep inner well can allow the bead of a tire to sink too low in one spot, allowing it to rise too high on the other end, leading to a blowoff. To compensate for this possibility, some rim makers made the overall diameter of the rim a few mm larger, which makes tire mounting even more of a fight, and then the tire might not roll very evenly due to the slop. Tubeless-ready rims fix this problem with a shallower mounting area along the sidewall, and by having a more precise location for the bead, the rim diameter does not need to be as large to prevent blowoffs.

As mentioned before, technique has a lot to do with it. While mounting the tire, make sure that the bead is hanging out in the deepest part of the rim well, so that you have more slack to get the last bit of the bead over the rim. You should be able to do it without tools.
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Old 08-04-17, 07:19 AM
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Having 15 wheelsets, gatorskins working as well as anything with southern AZ thorns, arthritis in my hands, needing to carry a Kool Stop tire bead jack with newly tires tires for flats, I would love to see a data base with problematic rims, tires, and rim/tire combinations.
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