New Mavic Open Pro

[Samuel D]

Is the 87 PSI (6 bar) a universal limit or just the worst-case scenario (28 mm tyres or whatever)? If Mavic doesn’t say so, I’d treat it as the worst-case scenario. Nothing else makes sense to me.

Regarding the decrease in spoke tension when inflating the tyre: what spokes were used? Perhaps there’s a case to use especially thin spokes with this rim (e.g. 1.6 mm).

[Brucey]

there is a sticker on the rim that just gives a maximum tyre pressure. Maybe the previous arrangement (which had a max pressure that varied with tyre width on the sticker) just confused people; it should have done, they shipped thousands of rims with a misprint....

The spokes were 14/15g DB ones. I have little doubt that the problem would have been worse with PG spokes.

I recently built a front wheel with a comparable rim, and a 'normal' amount of tension (in DB spokes), and for the first time ever, in over 35 years of building wheels, the nipples started to back out in service. I didn't check the spoke tension with an inflated tyre; in future I shall do so with any unknown rim.

cheers

[The utility cyclist]

Directly from Mavic
6 bar for tubeless
7 bar for tyres/tubes = 101 psi, more than enough for most and the wider rim (minimum recommended tyre is 25mm, max 47mm) will stretch a 25mm tyre closer to 27mm anyway. If you need a higher PSI than 101 with a 25mm/psuedo 27mm then maybe you need a wider tyre for the job or indeed are looking at the wrong rim if needing really high pressures on a narrow rim/tyre.

[Samuel D]

I will grant those pressures are “more than enough for most”, but they still limit a lot of people. I only weigh 65 kg and I’d hit those limits on a rear wheel with 23 mm tyres or 25 mm tubeless tyres.

However, if those limits are supposed to apply even to massive 47 mm tyres, I’d simply ignore them with narrow tyres.

Then again, maybe this is the first rim in existence with a tyre pressure limited by collapse of spoke tension!

EDIT: just checked the Mavic website for this rim. The specifications say “Recommended tyre widths: 28 to 47 mm”. With at least a 28 mm tyre, the pressures become a good deal less restrictive.

[Brucey]

I wonder if the pressure limit is at least as much as anything low because the UST rim has only a very small crotchet (hook bead), such that at higher pressures, tyres are at risk of simply blowing off. Utility cyclist's Mavic info suggests that (as you might expect) with an inner tube, pressing the tyre beads into the hook reliably, the allowable tyre pressure is a bit higher.

The reduction in spoke tension is higher than normal with rims of this shape I think because the braking surfaces rotate slightly and this helps the curved sides of the main hollow section straighten, allowing the spoke bed diameter to move inwards slightly. Quite small variations in the rim design might greatly reduce or even combat this effect. For example Da Vinci have made rims (V22 and V23) that are slightly different in external shape, and have additional webs inside. These rims are heavier but are suitable for tandem use.

This is the archetype rim section



which suffers from pressure-driven tension reduction more than I'd like and this




is the V22 design ('new' about 15 years ago I think) and the current V23 rim, which I'd expect to be better in this respect.

cheers

[The utility cyclist]

I will grant those pressures are “more than enough for most”, but they still limit a lot of people. I only weigh 65 kg and I’d hit those limits on a rear wheel with 23 mm tyres or 25 mm tubeless tyres.

However, if those limits are supposed to apply even to massive 47 mm tyres, I’d simply ignore them with narrow tyres.

Then again, maybe this is the first rim in existence with a tyre pressure limited by collapse of spoke tension!

EDIT: just checked the Mavic website for this rim. The specifications say “Recommended tyre widths: 28 to 47 mm”. With at least a 28 mm tyre, the pressures become a good deal less restrictive.

I weigh 102kg, one of my clincher sets I have a true 26mm rear and a 25mm front on my carbon bike when I'm not using tubs. These are at 105/90, god knows why you'd want to have tyre pressures that high on normal roads, 90/75 with a 23mm tyre would be more in line with a usual set up for your weight + a std road bike and even fitting 23mm on the wider OP would mean an even lower tyre pressure still.
As I said though if the pressures are too low then clearly this isn't the rim for you.
I would absolutely disagree with your premise that a "lot of people" would be limited by the max tyre pressures, in fact I'd say hardly anyone at all except those wishing to go touring/loaded on really narrow tyres (which these rims aren't designed for anyway) and then for a lot of people these aren't touring rims and virtually no-one wants to tour/be heavily laden on 23mm tyres with all due respect to your own choices.

[The utility cyclist]

Brucey, max pressure for tubeless is a safety thing, there's been a lot of instances of tyres simply blowing off at high pressures that a tubed tyre wouldn't.

[Brucey]

Brucey, max pressure for tubeless is a safety thing, there's been a lot of instances of tyres simply blowing off at high pressures that a tubed tyre wouldn't.

Sure. What I find a bit confusing is that Mavic have chosen to implement the UST standard (which is presumably meant to be OK with tubed tyres too) without much of a rim lip/crotchet/hook, so that even tubed tyres are not much better off at high pressures. Would it really have compromised tubeless performance if the hook had been bigger, I wonder?

cheers

[Gattonero]

Is the 87 PSI (6 bar) a universal limit or just the worst-case scenario (28 mm tyres or whatever)? If Mavic doesn’t say so, I’d treat it as the worst-case scenario. Nothing else makes sense to me.

It's not a rim to fit <23mm tyres, so with 25mm you're pretty good with 87-90psi. Why going for higher pressure negating those benefits of a wider tyre?

[Gattonero]

I wonder if the pressure limit is at least as much as anything low because the UST rim has only a very small crotchet (hook bead), such that at higher pressures, tyres are at risk of simply blowing off----

Nonsense.
Other Tubeless-compatible wheels with similar small hook are rated to higher pressures (i.e. Campagnolo "two-way" wheels) and tyres don't blow off.
It works by using not only the hook, but the whole area and radius of the tyre bead.

[Brucey]

well it is a few months down the line and folk have been building up and riding on these rims.

I was somewhat alarmed when I measured the braking surface thickness on a pair of non-exalith rim brake rims; I got thickness measurements of 1.0-something mm, which I'd normally associate with a rim brake rim that is worn out, not new. If the exalith model maybe this thickness is adequate, but I'd expect a non-exalith rim to have some wear life in it rather than virtually none.

A chap I know has been running a pair of these rims (with ~28mm tyres) for the last nine months or so on his 'road bike' which is used for audax and fast runs, mainly in good weather. He went for fewer spokes than I would have (with that rim) and uncharacteristically he did break a few spokes in the rear wheel, mostly at the nipple end. The chap that built the wheelset for him stress-relieves wheels by leaning on the rim, and was of the view that he had 'gone easy on it' because it would otherwise be liable to collapse the wheel.

The rider had previously used a rim that was 2mm narrower internally and 50-70g heavier, same number of spokes. Over two years he had very little trouble with that wheel by comparison; IIRC it may have become evident that the NDS nipples were in need of threadlock but that was about it. I am wondering if the breakages with the Mavic rim were perhaps because the NDS spokes were going completely slack at times, and even buckling in compression, which bends the spoke near the nipple.

Because of the breakages the wheel was due to be rebuilt with new spokes, and there was a plan to try a different stress-relief method on the wheel just in case it wasn't the buckling thing. However the whole plan was put on hold when it was noticed that the rear rim had, despite local thickening, cracked longitudinally near several of the spoke holes, despite summer use only (no road salt which definitely causes cracking in some rims). The wheel (which needs to be used pronto) was rebuilt with the same type of rim that had been used previously.

So not exactly a stellar first outing with these rims, then. The inevitable question is if the spoke tension was too high. I suspect it was over Mavic's recommendation (which is pretty low IIRC) on the DS, but not by too much; a failure in summer use is not encouraging almost regardless of tension.

[ BTW re the rim design and tyre retention; 'nonsense' as per the above post is not a useful comment. The idea that friction alone is a reliable method of tubeless tyre retention is not a sensible one; UST tyres have thicker, stiffer and heavier beads than non-tubeless tyres and it is these beads that keep the tyres on the rim. Because the rim seal can be anywhere (the tyre lip or the rim lip) when running tubeless there may be no real tyre retention benefit from either friction or the hook bead. Manufacturers of such rims therefore routinely allow higher pressures to be used when tubes are fitted; the hook bead (and simple friction to some extent) will definitely help retain the tyre when a tube is used whereas with tubeless fitment it is not guaranteed that the tyre is held on by anything other than the bead and the tubeless fitment is inherently less secure.]

cheers

[Cugel]

It's a pity there will be no 36. But maybe the exalith finish will be used with other rims. I find Open Pro a bit dent prone anyway.

Paying a lot more for something (caramic/tungsten carbide/exalith) that greatly extends rim life can pay off. It has for me. My wife is riding on Open Pro Ceramics that must have done at least 8000miles and show no sign of wear yet. My own tungsten carbide impregnated CSS rims date from the times of King Tut and the braking surface is still completely flat. Both had braking issues, now resolved, but the CSS have so far triple normal life, and the Ceramics look like they are going to last very well. I'd be willing to pay double for a rim that held out a realistic hope of exceptional durability.

I have a pair of wheels built with Mavic ceramic rims and 36-hole Shimano 600 hubs that are sealed with rubber caps. I got them some time in the 1980s and stopped using them around 2007. They must have done tens of thousands of miles, including some racing miles. Apart from a very small flake of ceramic fallen off where I banged the rim on a sharp edge. they still brake superbly in the wet and dry using ordinary brake blocks - which they do tend to eat and which do require rim cleaning from time to time to take off brake block deposit.

Another poster mentions that long use of ceramic and other such braking surfaces will eventually smooth them. This must be so but I have to say that these venerable ceramic rims still brake much better than any of the standard alloy rims I have, especially in the wet. I use them very occasionally in an old bike (their narrow rims are not really made for the wider tyres I now prefer). The advent of these new exalith rims will, if no bugbears emerge, tempt me once more to buy a pair of handbuilt wheels, perhaps with matching super-resilient hubs, in the hope that they will perform as well as these old ceramic-rim wheels.

Cugel

[The utility cyclist]

I bought a ksyrium pro exalith, i'll measure the rim thickness out of interest.

[peetee]

Rapid wear characteristics are not confined to Open Pro rims. I have seen the same issue on A119 rims. I would expect them to be made of inferior material being a budget choice but their predecessors the MA2 certainly lasted longer.
Still happy with my Wolber GTX choice though.

[mig]

i wonder how much real world, practical testing is done on a new design on rim? how many different ways they may be built up, different tyres used, different spokes and how many miles they are ridden before they go on sale.