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I have a set of ZTR Rapid rims that are tubeless compatible, but I never run tubeless tires on them. They have this list of maximum pressures on the side of the rim:

Maximum pressures on the rim

Since the limits are dependent on tire size, I assume that the rim is structurally sound enough to withstand at least the highest pressure listed. And since I've never seen pressure limits of any sort on traditional rims, I assume that it's somehow specific to tubeless tires. But that's an awful lot of assuming...

So my question is twofold: Why the different limits for different size tires? And are they specifically for tubeless, or do they apply to tubed tires as well?

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As for rim strong enough for highest. The force the rim must take is both psi and size. If you have twice as many molecules pushing 1/2 as hard the total force is the same. It is not exactly force on the rim bead but the force on the tire to pull it off the bead.

Here is a reference where they give different pressure for tube versus tubeless. Hutchinson tires information See question 7. I just bought some Pyranha 2 CX tubeless and the pressure on the box is different from the pressure on the tire. Box is clearly the tubeless pressure as it is in the tubeless mounting instructions.

It is a lot about how the and where tire engages rim. On Stans (ZTR) the bead is shallow so you get more tire evolved in the adsorb rocks side. On Stans I would assume they mean max pressure period until you see a different pressure listed for with tubes. Their story is with a more shallow rim you need less pressure. See the diagram in this literature that standard rim with tube engages differently.
Comparison of a standard bicycle rim to a Stan’s BST Rim

How the different rims do UST varies. And how they cross to tube varies. Some have more of a dual type of engagement and some are designed just for UST.

ztr_rim_specifications

Stan’s rims are a tubeless design and care must be taken when using tubes.

If you want to go both ways then don't go Stan's.

Stans has great support - you should try and contact them.

See the two diagrams below. The first is a Stans and the second a Mavic. In these examples the Mavic has a separate groove for UST - a tube tire will be on the outer part of the rim. According to DWGKNZ the Mavic will seat on the outer even tubeless. Still you have different designs and some are designed for tubeless only and some fro both ways.

ZTR ArchMavic CrossMax

I am learning from comments from DWNG.
UST is a tighter standard than I was aware. The bead must have a specific design.
UST tubeless-tire system
There are still variations in the implementation. Some rims will cross over better than others.

  • The bottom picture below shows a profile of a UST rim, but not of a seated tire. UST rims have a design that sits the tire in the inner groove to allow it to be inflated with a hand pump. – DWGKNZ Aug 14 '14 at 21:06
  • @DWGKNZ So you are saying that when that inflates it will seat in the outer. That makes sense. Still I contend they have different designs and some cross over better. I have to admit that is is much easier to seat my Mivac. – paparazzo Aug 14 '14 at 21:10
  • Yep exactly. Other point to note is that UST is a standard that sets rim hook and tire bead design. A rim or tire carrying the UST logo will have to meet the set design standard, it doesn't allow variation. There are other standards emerging such as Bontrager's Tubeless Ready (TLR) and other various shared systems which are a lot more interchangeable with tubeless tyres. UST generally allows for pressures of 35-65 psi. – DWGKNZ Aug 14 '14 at 21:22
  • @DWGKNZ I will update my answer. But I feel like you should go ahead and post an answer. – paparazzo Aug 14 '14 at 21:56
  • The video that shows how a UST seals is here: pinkbike.com/news/To-The-Point-UST-Rims-Tires-2013.html – DWGKNZ Aug 15 '14 at 0:38

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