Does Gravaa Wheels on the Fly Tire Pressure Adjustment Work?

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You will have undoubtedly seen that the living legend of the sport, Marianne Vos, took yet another world championship title a few weeks back at the UCI Gravel World Championships in Belgium — a nice way to round out the year for one of the greats. Well, round out the “summer season” at least, before she changes disciplines and goes all ‘cross.

The gravel worlds course, as it has over the past three years, had the internet cycling community in a froth again. Was it gravel? Is it gravel? What is gravel? You know, the usual arguments — sorry, “friendly debates” — that occur. The course took in everything from bike trails, pavé on narrow, steep streets, farm tracks, a loop-the-loop bike lane through a major train station, clonking draggy Belgie concrete roads with the tire-width Death Valley running down the center (you’ll know what I mean if you’ve gotten to race there) and of course a touch of gravel. Shall we call it a multi-terrain race, as opposed to pure gravel? Still, what is gravel (answers on a postcard to…)?

The race came down to the wire; Vos outsprinted Lotte Kopecky for the win, and one factor that may have come into that final sprint win could very well have been the wheelset that Vos was rolling on. The all-new, production-ready Gravaa wheelset.

If you’re unaware of what Gravaa is or what the brand offers, that’s quite understandable. It’s a small company out of Eindhoven, Netherlands that over the past seven years has been working towards a wheelset that offers self-inflating and deflating capabilities on the fly. Two years ago, the tech was seen in action under the Jumbo-Visma team at the spring classics, with Wout van Aert using the wheels to get second place at Paris Roubaix. Back then, the wheels were in prototype form, and in the two intervening years, the Gravaa engineers have been beavering away to bring the product to market.

The system, dubbed KAPS (Kinetic Air Pressure System), is built into the front and rear hubs. The system uses kinetic pumps inside the hubs that are driven by the rotation of the wheels to allow inflation and deflation. Two satellite sifters are located on the bars to control this. One button push either pumps the tire to its pre-established PSI percentage or deflates it by the same amount.

You program the set-up through the Gravaa phone app; for example, on my test bike, I had it programmed to inflate or deflate by 0.5 bar on each button push. It’s all highly customizable, so if you want to deflate by 0.5 and inflate by 1 bar, it’s possible. Depending on the tire size, there are limits to how hard and soft you can go.

For the set-up I used (Reserve 40/44GR wheels with Vittoria Terreno Dry 38mm tubeless tires), I could go from a minimum of 1.4 bar to a max of 3.4 bar. Your desired and current tire pressure, front and rear, is read out on your GPS head unit. Deflation is pretty much immediate, with inflation only being able to rise by 0.8 bar per kilometer; this is down to the pump using the kinetic energy. So, the faster you go, the quicker you will achieve your desired pressure. If this sounds all a little complicated, trust me, it isn’t! For someone who actually explains it better, hit the play button as I chat with Loek Luijbregts, chief marketing officer at Gravaa.

The whole set-up adds a claimed 450g to a conventional wheelset, with two wheelsets being available at launch. Gravaa has partnered with Reserve to offer the 40/44GR wheels with the Gravaa system for €3,898 and with DT Swiss for the GCR500 wheels that will retail for €4,398.

I got to test the wheels back when the cycling-mad Belgians hosted the 2024 UCI Gravel World Championships. So how did they handle?

Let’s cut to the chase; the short ride around part of the UCI Gravel World Championships finishing circuit didn’t give me a good enough taste of what the system is truly capable of. I only had it for over an hour, and in that time, it was more of a learning curve than a true test of its capabilities. But it certainly seems to offer what it’s supposed to: on-the-fly tire pressure management. And it’s noticeable. If you hit a trail and it’s way worse than you had planned, you’ll be able to get to the lower pressure without too much of a worry. On the flip side, inflation speeds are noticeably slower, and getting a noticeably higher pressure takes time, but it certainly achieves its aimed pressure.

Ok, I’ll start with a negative. It’s not a big one, but I feel the shifter buttons could do with some work. They are lacking in tactile feedback. You can feel a click and movement, but the clicky positive feel isn’t on par compared to Shimano satellite shifters or SRAM’s blip buttons. The buttons that Gravaa is using are actually the same as what Classified Power shift hubs are controlled by, both being brands from northern Europe and being close to one another, which has resulted in them sharing a bit of tech. They work nicely enough, though. You know you’ve pressed them, but they’re a touch springy in feel. I’d love to be able to use Shimano’s or SRAM’s satellite shifters instead, but neither are known generally to partner with others outside of their own ecosystem. But we can live in hope; if I’m honest, it’s purely a nitpick. Nothing too major and something I’m sure if used for a more extended period would be adapted to easily and unnoticed in the long run.

Aside from the performance of the inflation system, the wheelset, in my case, the Reserve 40/45GR, as a whole, does not lack anything in performance when compared to a standard set of gravel wheels. Sure, they’re heavier, but that didn’t really affect the ride I had, as it was mainly on flat or short, sharp climbs. And that four watts of reduced drag, pah, that’s impossible to notice.

The price is €3,898, which is a large wedge of cash to put down on a set of wheels. But I feel it’s a relatively fair price for the system. It’s roughly an extra €1,000 on top of what that standard wheelset costs. Currently, the two options are either the Reserve 40/44 GR at €3,898 (€2,799 if you were to buy them without a Gravaa system installed) or €4,398 for the DT Swiss GRC500 (€2,911 for the standard wheels). The price will be expensive in many eyes, but I’d argue that it’s bringing something to the scene that hasn’t been done before. Yes, Scope tried this a few years back but ended up abandoning it, as Gravaa has persisted and now has a product ready for the masses.

Not to knock one down to raise the other up, but when compared to a pair of uber-luxurious Lightweight Schwarz ED that retail at €4,620, which, let’s be honest, is an insane price to pay for a set of wheels, the Gravaa system seems somewhat reasonably priced. I’ll add that I am sure the Pfadfinder Evo are lovely, like many Lightweights goodies, but that’s bank balance-busting prices.

Luckily the price is a damn sight more accessible than when the wheels were still in development. Gravaa claims that the version that WVA used two years ago in Roubaix would have cost in the region of €20,000. Gravaa also readily admit the new system doesn’t perform quite as well as that prototype set, but to bring the product down from a bespoke one-off item to a product that thankfully costs a fifth of the prototype price there’s going to be a few changes that needed to be made understandably. Whatever the changes were, the system works, and those changes don’t scream out at you. Basically, it doesn’t feel like any major corners were cut to hit the consumer price.

Who’s it for? Well, obviously, it’s for those that gravel, that goes without saying. But is it just for those that race? It’s aimed to bring a competitive edge, especially if we go by their first gravel victory. So it certainly leans heavily in that direction. And it’s where, I guess, we will see this most in use. I don’t think it’s a product idea for all riders; the learning curve may be steep enough to put some people off. Adding another dimension to your bike’s mechanics to think about when riding and racing won’t be for those who want purity when out on the bike. In the time I rode it, I certainly didn’t get things right about when and where to inflate and deflate, knowing how long it would take or how often I could. You’re not going to get the best experience or use out of this product on your first ride or even your first few rides (unless you’re Vos).

Is Gravaa on to something here? Or is it a product that will go the same way as L-shaped cranks, chainstay-mounted rim brakes or those zip-off tires? Personally, I think it’s a fresh idea, and it definitely brings something new to the gravel world. It’s not a rehash of an old idea (as far as I’m aware) or a change to an existing product purely for marketing purposes.

Gravaa is bringing something genuinely new and innovative to the market. And for the most part, it works well enough to be something I want to test further rather than dismiss it as a fad or gimmick. I had a few teething issues with the first bike I used it on, and hopefully they’ll be ironed out by now. It’s a product that, though expensive, does promise to offer noticeable real-world performance gains for its price. Yes, €3,800 is a lot of money, but compare that to the glut of items that provide watt-saving gains at exorbitant prices, such as ceramic oversized pullies at €700+ or aero socks that you can drop up to €1,000 on, and it seems a fair price.

I don’t expect to see it on casual gravel riders’ bikes any time soon, but I can see it being adopted over the next few years by those who race seriously. Marginal gains were once a buzzword in road cycling, and it’s coming for gravel, and Gravaa offers a dose of it.