When tubeless tires first became popular on mountain bikes, it was their resistance to pinch flats (above) that made them popular. Off-road, there are few nails or broken bottles that can cause punctures (and even those usually will be pushed into the soft ground rather than puncture the tire), but rims can bottom out on sharp rocks and other obstacles. So much so, in fact, that top mountain bike racers used to race on tubular tires – because tubular rims make pinch flats less likely. Eliminating tubes did the same, and while you still could ‘burp’ the tire, in general, tubeless allowed running lower pressures with fewer problems.
Many also believed that tubeless tires were faster. It made sense: an inner tube, even a thin one, added a membrane that flexed and absorbed energy. A tire without a tube had to be faster, even if only by a small amount! One big manufacturer advertised their tubeless tires with the slogan “Nothing is always faster than something.”
This turned out to be another myth. Tubeless tires have real advantages, but speed isn’t one of them. To seal the tire, you have to add sealant. Pouring liquid into your tires inevitably slows them down. Old-timers tell stories of how they put water in the inner tubes of their friends’ bikes as a practical joke. The inertia of the water made the bikes impossibly hard to pedal.
The website Bicycle Rolling Resistance (www.bicyclerollingresistance.com) measured tires with and without sealant (above). Testing on a steel drum measures only the hysteretic losses, so ignore that the graph shows higher pressures having less resistance. (That isn’t true on real roads.) But for the effects of sealant inside the tires, it’s the hysteretic losses that are important, so the drum test works in this case.
What you can see is that once you add enough sealant (40 ml) to have actual liquid inside the tire (after the tire casing has become saturated), the energy required to turn the wheel increases significantly.
Our own testing confirms this. We tested the very same tires mounted tubeless with as little sealant as possible – a best-case scenario for tubeless. Then we removed the sealant and installed tubes. The tires rolled at almost the same speed. Even with almost no liquid sealant inside, the tubeless setup rolled only marginally faster.
Riding the tires with that little sealant is inviting trouble. I set up another wheelset the same way, and the tires worked themselves loose from the rim walls when the sealant dried up a week into the experiment. (Supple tires always move slightly on the rim, and sealant is necessary to keep tubeless tires sealed on the rims.) Once you add enough sealant for the tire to work reliably, it will be slower than it was with a lightweight inner tube.
How about making the tires themselves airtight? There are tubless tires that you can run without sealant, but to make these tires airtight, they need thick rubber coatings on their casings. And this makes them less supple, so they are in effect slower than a more supple tire with a lightweight inner tube – as shown by the steel drum test of a Schwalbe Tubeless vs. Standard tire (above, from http://www.bicyclerollingresistance.com).
Most of these differences are small. A tire set up tubeless won’t be faster than a lightweight inner tube, but also not significantly slower. The simple fact is that a tube, especially a lightweight one, is extremely supple and adds very little resistance. The sealant required to run a supple tire tubeless will cancel out the gains from eliminating the tube.
What will be significantly slower on real roads (much more than the drum test above suggest) is an airtight ‘tubeless’ tire, since its stiffer sidewalls don’t absorb vibrations as well, which increases the suspension losses. Better to add a little sealant to a not airtight tire, if you want to run tubeless…
Tubeless tires have their place: They are great for preventing pinch flats, and most of Compass’ wider models, which are intended to be ridden off-pavement, are tubeless-compatible. And yet for most of us, pinch flats aren’t really an issue any longer, even on gravel roads, because we now run wide tires – mostly because they roll faster on rough surfaces, but also because they are less likely to bottom out and pinch-flat.
What about puncture resistance? The sealant inside the tires can seal small punctures. However, in my experience, the hassle of dealing with the setup and maintenance of tubeless tires outweighs the hassle of fixing the occasional flat tire. If you want the simplicity of tubes with the puncture resistance of sealant, simply pour some sealant into your inner tubes – many riders report that this self-seals punctures, too.
In the future, I will run my tires tubeless when I ride across really rough terrain – like our recent passhunting adventure in Japan (above) – but not for my normal riding on paved and gravel roads.
If you’ve been curious about running your tires tubeless, check out the illustrated how-to guide on setting up tires tubeless in the Spring 2018 Bicycle Quarterly. With the right technique, it’s possible to seat the tire even without an air compressor. This makes it easy to set up tubeless tires at home or even when traveling.
- Hysteretic losses due to sealant (www.bicyclerollingresistance.com)
- Test of tubeless vs. standard Schwalbe tire, showing that the airtight tubeless version is slower (www.bicyclerollingresistance.com)
- Other posts in this series:
– Myth 1: Wider tires are slower
– Myth 2: Titanium is lighter than steel
– Myth 3: Fenders slow you down
– Myth 4: Stiffer frames are faster
– Myth 5: An upright position is always more comfortable
– Myth 6: Tread patterns don’t matter on the road
Photo credits: Ryan Hamilton (Photo 1), Westside Bicycle (Photo 2), Natsuko Hirose (Photos 6 and 7).