Tubeless is slowly but steadily taking over in the road wheel market. While only a small minority of road cyclists use tubeless tyres, virtually every new wheel and rim offering on the market come as tubeless ready or tubeless compatible. Some rims are even certified with a Universal Standard for Tubeless (UST) logo. What it means for you and me is that you don’t need to bother sealing the rim internal holes with tubeless tape and you can simply fit the tyre onto the rim as you would in a car. Mavic use this technologoy for all their MTBike wheels and have a limited range of these rims on offer for builders, although they are all marketed in their mountain bike section. Of course MTB 29er and road 700c are the same 622 mm internal diameter and generally speaking they are interchangeable, although the former are often too wide to accept road tyres having a diameter of less than 30 mm and the latter are typically too narrow to accept large MTB tyres, always exceeding 50 mm in diameter. This would in theory means the two standards are meant for different applications, but with road tyres as well as rims getting increasingly wide, the boundaries are now blurred.
This is certainly the case for the Mavic XM 819, a disc specific, UST rim considered too narrow for modern 29ers and often disregarded by cyclocross fanatics too, who look at Stans Iron Cross or Grail for their hand built wheels. So, does it work with road tubeless tyres?
I did order a heavily discounted 2015 pair of rims and before building them, I had a go at fitting a pair of 25 mm IRC Roadlite and yes, they do indeed fit, although they are quite tight, which also means they jump onto the rim ramps with just a couple of shots of a track pump and loudly click into place. The rims come with their own tubeless valves, which are however incompatible with my Stans injector, so fitting the sealant was a bit of a pain. The fun things about these rims is that you can build them with the tyre on and even at the required pressure if you so wish. They come complete with the FORE threaded cups to insert in the holes, with a drop of Loctite and torqued anticlockwise with the 6 splined 9 mm FORE tool. Mavic advises to use 16 mm nipples with these, but I found the more widely available 14 mm ones to be more than adequate, as the square section clears the cup nicely and leaves plenty of room for the spoke key to work on.
The rims are also drilled with an offset, which means the final tension spread for a disc wheelset is around 70/100 L/R at the rear and 100/70 L/R at the front, much healthier than the typical 100/50 of non offset rims. The arrow in the photo above is misleading, as it does not indicate the rotation direction. The rims are built with the appropriate side visible from the drive side of the bike. So you will read front for the front and rear for the rear rim. Rims + FORE cups for the 29 er size weigh around 500 grams each, so a tad more than other rims, but then you don’t have to fit rim tape, which probably means they end up weighing the same. The ERD is 594 mm, measured with 12 mm nipples, so if you build them with DT swiss 14 mm ones, you need to work out the spoke size you require with the DT calculator or using 590 mm as ERD if you plot them in a calculator with no nipple choice.
And here’s the final result of a 32 H, built 3 cross with Sapim Race for my single speed disc conversion.
And here they are on the bike, taken for a spin. I use a 80 PSI tyre pressure and all seems buttery smooth with no problem at all.