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CX tubeless: Can it compete with tubulars?

Racers will find a lot to like in the latest tubeless cyclocross setups, but you might not want to ditch your tubulars just yet.

Every fall, the mavens of cycling start fielding the eternal question: what wheels and tires to run for cyclocross? There’s no argument that wheels are the single most effective performance upgrade a rider can make, and tubulars are obviously the clear leader in every perceivable performance category. However, tubulars are a big step up in commitment, and some racers just aren’t up for the hassle. The good news is that tubeless has been doing some serious catching up and might be the ideal choice for those looking for a performance upgrade without the headaches of tubulars.

The adoption of tubeless technology in cyclocross has been very slow. The rest of the wheel-oriented world has popularized tubeless technologies to the point of ubiquity — even the mountain biking world loves tubeless. So why is it such a hard sell for cyclocross?

Simply put, it’s all about volume versus pressure. Mountain bikes can run low pressure because they have the volume to support it. Road tubeless has very little volume, but the pressures are much higher. Cyclocross is right in the middle. ’Cross riders want to run super-low pressures, but there’s not enough volume to absorb stresses on the tire at the rim — stresses that are commonly the cause of burping, which is a tubeless tire’s Achilles heel.

The good news is that tubeless setups have become vastly more reliable and overall performance has improved. The better news is that a lot of the guesswork has been taken out of matching tires with the right wheels for optimal performance; everyone’s playing nicely together now.

Wheels

It has been a long time coming, but tubeless is becoming more standardized. Bead diameters are more consistent and tires are improving, so overall, tubeless is seeing gains in performance and reliability.

Carbon clinchers like Enve’s 50/50, Stan’s Valor, and Bontrager’s Aeolus 3 TLR sport weights approaching that of race tubulars. At 1,340 grams, the Valors were the lightest of the wheels we tested. Also, rims continue to get wider, ranging from an inner-rim width of 19mm on the Ritchey Zeta WCS and the Easton EA90 SL, 19.5mm for the Bontrager hoops, and up to 21mm on the Stan’s and Enve rims. The European Tyre and Rim Technical Organisation (ETRTO) has worked out optimum inner-rim widths for every conceivable tire diameter, and the recommended inner-rim width for a cyclocross tire is 18-22mm. These wider rims offer more stability, casing flexibility, and safety than narrower rims.

There’s a long and boring explanation for all this, but for now look at it this way: Stand with your feet together and get someone to give you a good push from the side; you will fall over, right? Now stand with your feet farther apart, maybe a bit wider than your shoulders, and ask for another shove. The increased stability produced by the wider stance will make you hard to topple. Same goes for tubeless: even in cases of considerable lateral forces or hard cornering at low pressures, if the directional load on the tire is centered between the rim walls, the tire will be far more stable, harder to collapse, and harder to burp.

But in cyclocross, there’s definitely a tipping point at which the rim is too wide for the tire, and past that point, performance will suffer. With some of the repurposed mountain bike wheels (21mm inside), we found a higher propensity for sidewall cuts and decreased suppleness when we used narrower (32mm rated) tires. This happens because the sidewall actually tapers inward from the rim instead of forming a pregnant curve, exposing the sidewall where there’s less tread to protect it. The basic rule here is that whatever the wheel/ tire combination, the tire should scribe a consistent and somewhat bulbous sidewall curve to maximize flexibility, suppleness, and flat resistance. We found the 21mm inner width rims to be a bit too wide for some of the narrower tires like the IRC Serac.

And then there’s the question of how rim width affects the diameter of the tire when mounted. The short answer in the case of cyclocross: not much. Adding 2mm of rim width — say, moving from a 19mm inner-width rim to 21mm — while using the same tire adds 2mm to the circumference of the whole but only adds just over 1mm to the overall diameter once mounted. The bigger issue is how the tire rides when mounted on a wider rim. This variable is the hardest to predict.

Tires

Tubeless tires for ’cross used to be stiff and harsh, with ineffective tread patterns and limited options. We tested a random sampling of tubeless-ready tires and found the Serac range from IRC to be surprisingly good. Intelligent tread designs, supple casings, and excellent tubeless sealing and tire retention make IRC tires a standout option.

More tubeless options are hitting the market this season, including Schwalbe’s X-One variety spotted at Interbike this year. Also, Vittoria offers a 320 tpi, tubular-grade casing design that will be extended to cyclocross tires, while Clement’s MSO will go tubeless in November followed by PDX, MXP, and the new BOS in early 2016. We also enjoyed flat-free riding with Maxxis’ Mud Wrestler, which has a rather versatile tread pattern.

Beyond tires and tread, sealant is another evolving component of tubeless technology. However, as far as we can tell, there isn’t much differentiation between sealants. Stan’s has gone green (as in enviro-friendly), Orange Seal is still orange, and Caffélatex is still bubbly. Many other manufacturers have their own versions that were not included in this review, but sealants are mostly a similar viscosity and most seem to work reasonably well until they get old or dry out in extreme cases. We encountered a small sidewall cut (less than 1/8-inch) in the last couple of days of our review, and although we were able to seal it up in the garage at home, on the road it leaked and spewed sealant until all the sealant was gone. This was quite frustrating, and it cast tubeless’ limitations into sharp relief. The problem of sealant going bad in the tire (separating or congealing, for example) is ever-present and requires a little bit of management on your part.

Weight

When it comes to weight, tubeless comes close to tubulars when you have similar rims. As a comparative experiment, we weighed front wheels with tires or tubulars, rotors and skewers. When framed this way, the Stan’s Valor wheel, ready to ride, was 1,210 grams, and the Enve 50/50 with an IRC Serac tire was 1,310. But a handbuilt tubular Enve XC with DT 240 hub and Clement PDX tubular was 1,100 grams. So the tubeless setups are definitely in the ballpark, but the lightest tubular wheels still have a weight advantage over tubeless.

What happens when you put this all together is pretty impressive. We’re very much used to the performance of tubulars and found the best of the wheels combined with some of the better tires to be smooth, reliable and quite hard to burp, flat, or compromise. We ran low pressures almost on par with those of tubulars without issue and even managed to get grass caught between the rims and tires without the setups failing.

Bottom Line

Despite recent upgrades and improvements, tubeless still has some conspicuous drawbacks. Tubeless can’t approach tubulars when it comes to low tire pressure because at low pressures, tubeless tends to feel squirmy and unstable. Tubeless is also easier to flat by way of cutting a tire, since the rim walls are a lot less forgiving. However, we found that some of the best tubeless rim and tire combinations that we tested made for a smooth and reliable ride similar to that of tubulars.

While you won’t see a tubeless setup on the front row of a Superprestige any time soon, for home mechanics and weekend racers, tubeless is becoming a reliable and convenient race option that is sure to continue to grow and improve.