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by James Huang
February 12, 2020
Photography by James Huang
One of the biggest draws of modern high-performance clincher road tires is their low rolling resistance as compared to traditional tubulars. Whereas the latter has a gooey glue layer in between the rim and tire that sucks up precious watts, the former is more directly connected to the rim. The latest crop of high-performance tubeless tires is often considered to be better yet (fitment hassles aside), since there’s no rubber inner tube migrating around inside the casing, and liquid latex sealant that can help repair small punctures on the go.
That free speed — and the convenient self-healing — of tubeless tires are big reasons why tubeless is slowing gaining favor amongst the pro teams, such as Deceuninck-Quick Step, Bora-Hansgrohe, UAE-Emirates, and EF (along with, perhaps, some pressure from equipment sponsors). But as a recent study conducted by UK performance consultant AeroCoach LTD reminds us, the demarcation between tubeless and tube-type clinchers isn’t quite as clear-cut.
AeroCoach measured the rolling resistance of a variety of premium tube-type and tubeless tires, mostly focusing on models aimed at time trial racing, which typically prioritize low rolling resistance more than general-purpose racing tires. Included in the test group were several sizes and styles of the Vittoria Corsa Speed, Michelin Power TT, Specialized S-Works Turbo Cotton and S-Works RapidAir, the Schwalbe TT, Pirelli’s P Zero TT, and Continental’s latest GP5000 family.
Continental’s new GP5000 TL tubeless road tire finished roughly mid-pack in this test in terms of rolling resistance.
All of the tires were tested using the well-known and proven roller protocol, and latex tubes were used for all of the tube-type models.
“Our roller tests are run in combination and validated with outdoor velodrome testing (tarmac) as well as being able to use the Alphamantis system indoors if we want to,” said AeroCoach director Dr. Xavier Disley. “For this TT set of tires, we actually went one further and tested the tires in the wind tunnel, as well as roller testing, and then last Friday, we went to the velodrome and did a combined test to see how everything matched up in the real world.”
For the most part, AeroCoach’s findings were as expected: wider tires exhibit lower rolling resistance than narrower ones for a given pressure, and tires with thinner and more flexible casings are faster than tires with more robust reinforcement.
The top tire overall was Vittoria’s paper-thin 25mm-wide Corsa Speed – a tire that can be run with tubes or tubeless – followed closely behind by the 23mm-wide version of the same tire.
AeroCoach’s test data isn’t exactly comprehensive in terms of how many tires are covered, but the results are still quite interesting. Photo: AeroCoach LTD.
Slotting into third place was Michelin’s tube-type, 25mm-wide Power TT, while Pirelli’s tube-type P Zero TT came in fourth. Next in line were the tubeless 25mm-wide Schwalbe TT TLE and tube-type, 24mm-wide Specialized S-Works Turbo Cotton.
Continental’s new 25mm-wide tubeless GP5000 TL required more than seven additional watts per pair to maintain the 45 km/h target speed, however, while the 26mm-wide Specialized S-Works RapidAir soaked up another five watts of rider effort on top of that.
The Schwalbe’s Pro One is widely recognized as one of the fastest-rolling tubeless clinchers on the market, but it wasn’t included in AeroCoach’s test matrix.
Occupying the lanterne rouge position was Continental’s workhorse 23mm-wide tube-type GP4000, which, according to AeroCoach’s testing, required almost 12.5 watts more effort to maintain 45 km/h than the 25mm-wide tubeless Vittoria Corsa Speed. If you’re not well-versed in how significant that difference might be, rest assured that it’s quite a lot when it comes to going fast.
Overall, the biggest takeaway from AeroCoach’s latest round of testing seems to be that casing flexibility is the most important single determinant when it comes to rolling efficiency. However, it’s also interesting that AeroCoach found no difference in rolling resistance between a tubeless-ready tire that is set up tubeless with a latex-based liquid sealant, and one that has a high-performance latex inner tube installed.
Currently, tubeless tires offer a lot of benefits in cycling disciplines like mountain biking, gravel, and cyclocross. All of those are typically conducted in environments where flats – especially pinch flats – are more common than on the tarmac, and riders in all of those situations can greatly benefit from being able to run lower pressures than inner tubes would practically provide.
However, the argument for tubeless on the road has never been nearly as clear-cut. Road riders don’t generally need (or want) to go that low, there aren’t as many obstacles on the ground to contend with, and the quality of fitment is far more variable given the frustrating disparity in tubeless-compatible rim and tire dimensions. As a result, most road riders still stick with tubes (and usually butyl ones at that) for pragmatic reasons.
Alternatively, latex tubes like the ones AeroCoach used for testing here are a fair bit more expensive than even ultralight butyl tubes, and the more porous material doesn’t retain air as well long-term, either. However, there’s also plenty of testing data available that proves they’re substantially faster. AeroCoach pegs the difference at a substantial seven watts per pair, and dollar for dollar, they’re among the best performance values available. There’s a fair bit of anecdotal evidence that latex tubes are also more resistant to puncture and pinch flats than butyl, too.
Taken in total, the argument for tubeless, at least on the road, starts to feel pretty shaky.
Before you run out to replace your current tires with Vittoria Corsa Speeds, though, there are a number of caveats to keep in mind – and even AeroCoach is quick to point out that efficiency isn’t everything.
Consider, for example, the fact that Specialized-sponsored riders in the WorldTour have been dabbling with that company’s S-Works RapidAir tubeless tires, instead of the S-Works Turbo Cotton tube-type clinchers that AeroCoach’s data suggests are substantially more efficient. Is that the result of sponsor pressure to push the tubeless message, or the team’s bona fide desire to run something with sealant inside? That’s hard to say from here, but keep in mind that tubulars are still the norm, and they’ve already been proven to be slower than many high-performance clinchers, tube-type or otherwise.
Specialized’s new RapidAir tires have been making inroads in the pro ranks, despite the fact that the company has faster tires in its repertoire.
As you’d expect, all of the time trial-focused tires (including the Vittoria Corsa Speed) that did well in AeroCoach’s testing prioritize low rolling resistance above all else, including puncture resistance, grip, and durability. They’re made to go fast for short distances on good surfaces, and that’s about it. None of them are claimed by their manufacturers to be suitable for everyday use, or even for general road racing on routes that haven’t been recently cleaned.
So, as always, the need for speed needs to be weighed against other performance requirements such as traction, durability, and puncture protection – after all, what good is a fast tire if you have to repair it on the side of the road during a race? Pick your poison carefully.