Update March 15 – Long term update.
This has been in use for the last three months so we are now comfortable giving a long-term update and verdict. The word is it works. There’s no issues running tubeless and it barely loses air even after a week. The seal with the Specialized Purgatory tires is near flawless as the tire just feels so secure on the rim even at low pressure. The wheel is dead-on true and the bearings are even smoother now than brand new.
This validates to us the concept of straight wall rims with no hook bead. And even with a tubeless setup, the tire is on securely and holds air under hard cornering. The key issue we’ve learned is the tubeless seal is really more dependent on the mating between the horizontal part of the rim and the tip of the tire bead itself. This interface needs to be tight and that’s what holds the air in. It’s not really about the bead sidewall the hooked rim walls as we assumed before.
As far as rim strength and durability is concerned, we have not knocked this rim on any rocks so it is hard to judge. But we do believe it will hold up better than a hooked carbon rim simply because the rim wall structure is simpler and better supported.
At $1200 this is an impressive value with light weight, lateral stiffness, tubeless compatibility and the included axle cup adapters for all popular sizes.
Update Dec. 10 – Ride impressions and C-clamp test below.
These wheels arrived today and since we had such a good experience with our last Roval carbon wheels, we had to play with them right away.
The new wheels are wider internally at 23 mm and cheaper at $1200. Tubeless accessories are all included and end caps for different wheel standards are included too. The graphics are a little more neutral and attractive too as the signature Roval red is dropped for subtle white on black branding. Specialized realizes that this wheelset will be popular with other brands so this should go well with any bike brand or color.
Introduction and Description
Mounting the wheels tubeless with Purgatory tires
The wheel build is dialed as the tension for every spoke is recorded. The wheels are perfectly true and the tension is very high and even. DT Revolution spokes are used and the rear hub internals are DT Swiss as well.
And one of the best features of this wheel is many types of end caps are included. 9mm front, 15mm front, 9mm front for cross/road bikes, skewer and 142mm spacing for rear are all included. If one has to go with 20mm front axle, that is not in the kit but available from Specialized as well. These numbers may not make sense to most but trust us with the fact that this is the wheelset that will fit the most bikes. Axle standards are evolving these days and it is a big mess that is making many perfectly good wheelsets obsolete.
We’ve ridden these tubeless twice now in two days. The setup above is a Specialized Epic with tubeless Purgatory tires at 22 psi. Rider weight is 150 lbs and trail conditions were hardpacked, hero dirt singletrack and fire roads. The wheels performed flawlessly as the setup never lost air or burped under hard cornering. The wheels felt laterally stiffer than our 2012 Carbon Control Trail Rovals. Even thought the outside rim diameter is about the same as the previous year, the lack of a hook in the rim gives the wheel higher internal width. It is a bit early to tell but cornering and throwing the bike in and out of corners felt good.
A note about tire pressures:
Specialized does not state a minimum psi for these wheels. That is really a function of rider weight, riding style, terrain and tire fit. Mtbr will venture low into psi testing to see if these hold a tire as good as hook-bead rims. But please use common sense when setting your tire pressure. Start high and lower as you see fit with your riding experience.
So the real question here is do the rim sidewalls with no inner groove perform the job of holding the tire in place? Will they hold a tubeless tire secure and prevent the dreaded ‘tire burp’? A tire burp occurs when a tubeless tire experiences enough lateral force that it folds over and lets air out between the tire and rim interface. This usually is accompanied by a spray of sealant, a burping sound, and the thud of a body hitting the ground.
To expedite our testing and to save our carcass from the pain of crashing, we employed the crude but useful C-clamp test. First we set our tire to 12.5 psi (since low pressure is where burping occurs). Then we tried to yank the tire out of the rim. Nothing happened. We then got a c-clamp and placed it on the tire right above the rim. We tightened the c-clamp and wiggled the clamp and tire in an effort to get the air to leak. Nothing happened. We repeated this process again until the C-clamp was completely tightened with both sidewalls locked together. We wiggled some more to let the air escaped and we could not break the seal.
So this give us quite a bit of confidence with this new rim design and technology. It appears that a good rim, a good tire bead and a tight fit between the two are the crucial elements for a secure tubeless seal. And if tire and rim interface are secure when tubeless, using tubes will be no problem at all.