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Could adjustable air pressure systems work for mountain biking?

New hub-based system holds promise for cross country racing

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Keen gear-watchers spotted something interesting on Jumbo-Visma bikes Wednesday at Dwars door Vlaanderen.  What the WorldTour road team is testing could have a big impact in mountain biking, as unexpected as that might seem. Especially on the cross country side of the sport.

What happened and what is the system?

What’s the big deal? Well, Jumbo-Visma’s rider Edoardo Affini was spotted using an adjustable tire pressure system at a major road race. The idea is that riders can lower their tire pressure for rough, cobbled sections and then add pressure again for faster rolling tires on smooth sections of road.

The hub-based system is created by the Dutch brand Gravaa. It allows riders to automatically adjust tire pressure, without stopping or getting off of the bike, via a bar-mounted remote that connects wirelessly with the hubs.

The tires can be inflated or deflated at the push of a button. Gravaa’s KAPS (Kinetic Air Pressure System) requires no motors and, since inflating is powered by the bike’s motion, it is not limited in how many times it can add or remove air from the tire chamber.

Currently, Gravaa’s app will let you set custom pressure settings. You can also display current pressure on your existing cycling computer as a data field.

Haley Smith at Leadville 100. Not pictured: extended sections of smooth doubletrack and pavement. Photo: Wil Matthews

Why is that a big deal?

Inflatable tire pressure systems are not new. The idea has floated around in various stages of development for nearly ten years, if not longer. Start-ups like WhiteCrow and AirWinder either never went anywhere, weren’t practical for high-performance use or, simply, weren’t even trying to be.

But, if Jumbo-Visma is confident enough in the Gravaa system that it doesn’t consider running it at a race like Dwars door Vlaanderen, this is the furthest any company has advanced the idea. And the first time it’s reliable and sleek enough to be used in professional racing.

It is a big deal on road because Gravaa is claiming very impressive, double-digit power gains if its system is used on cobble roads as featured the upcoming Paris Roubaix. But the same principal could make Gravaa’s concept hugely important in mountain biking.

Luca Braidot and Alan Hatherly’s thrilling, and paved, sprint at the 2022 Lenzerheide World Cup XCO. Photo: Bartek Wolinski / Red Bull Content Pool

Could this work for mountain biking?

If this works, and can be applied to mountain biking, it’d be a big deal. Especially for cross country racers, though fat bikers would also have great use for it.

Think about marathon races like Leadville or stage races. These require racers to try to optimize tire pressure for crucial sections of paved roads or double track, where higher pressures offer better rolling speed, as well as decisive sections of technical singletrack where lower pressures are essential for traction. With the ability to adjust tire pressure without having to step off the bike, riders could choose the correct tire pressure all the time instead of compromising on a middle ground that works for both.

The system could also help if you burp a tire or get a slow-leak flat, depending on how fast air is escaping the tire.

Even World Cup cross country racers could potentially benefit enough to make this system worth looking at for pro riders. In 2022, the Lenzerheide, Switzerland cross country World Cup features a long, uphill drag to the finish line. That race was decided in a thrilling sprint (after some last-lap drama in the woods just before). If Gravaa’s system actually delivers the 20-60W power gains the brand claims, it could be enough to influence a sprint. It would definitely save energy on the same section of road on the other 6-7 laps of the race.

Gravaa’s XC-28 wheelset. Yes, that’s seven rotor bolts you’re seeing. Photo: Gravaa.

What’s the next step?

Gravaa clearly knows this could be a big deal for mountain biking. The brand already has an XC wheel up for pre-order. Gravaa’s started real-world testing of the system,  sending riders to the Gravel Migration Race recently in Kenya. Both the gravel and XC wheels looked like they were being tested there, based on photos. Gravel isn’t mountain biking, but it is an important step off road.

Gravaa’s XC-28 wheelset is heavier than most XC race wheels but, at a 1,990g claimed-weight, not totally unreasonable. It also uses a relatively modern 30-mm internal width. The proprietary hubs, which doesn’t look much bigger than Race Face’s Vault hubs, do require some compromises though. Gravaa’s created its own 7-bolt disc mount that only works with one of Gravaa’s own rotors. It does work with SRAM, Shimano and even Campagnolo freehubs.

Realistically, the next test will be on the road. With Tour of Flanders and Paris Roubaix both looming on the road calendar, and the latter specifically targetted by Gravaa, we’ll get a good sense of what Jumbo-Visma riders and mechanics think of the system based on whether or not we see it there.

But for any early adopters that already see advantages in the system, Gravaa does have the XC-28 wheelset up for pre-order. Committing early will get you the discounted price of €2,929.00. If you want to wait for more proof the system will work off-road, full retail is currently set at a staggering €3,255.00. That’s roughly $4,800 in Canadian dollars at the current exchange rate.