A Gravaa KAPS (Kinetic Air Pressure System) automatic tyre inflator system for gravel riding has been spotted at Eurobike 2024.The system made headlines in 2023 after it was spotted on pro rider Edoardo Affinis Dwar Doors Vlaanderen road race bike.Now, Gravaa is working with Reserve and DT Swiss to bring complete gravel wheelsets to market. Loek Luijbregts, Gravaa's chief marketing officer, told BikeRadar an MTB-specific version is also in development, alongside an updated road-going system.The system has been updated with smaller, sleeker sprint shifter-style controls and a new mobile app.Were also told that at least two bike brands have bought units from Gravaa, suggesting that the system will appear on OEM bikes in the not-so-distant future.From trial to realisationThe system was first spotted in 2023. - Jack Luke / Our MediaWe saw Team Jumbo-Visma (now Visma Lease-a-Bike) rider Edoardo Affini sporting a prototype Gravaa KAPS hub at the 2023 Dwars Door Vlaanderen spring classics race.This enabled Affini to adjust his tyre pressures on the move, via remote switches on the handlebar.In theory, reducing pressures on rougher terrain for example, up cobbled climbs could increase traction and minimise fatigue. Increasing tyre pressure for tarmac sections of the course would reduce rolling resistance.The system works using a clutch mechanism housed within the KAPS hub. With the clutch engaged, the system pumps up the tyre using the rotational movement of the hub via a tube attached to the spokes. KAPS feeds air to the tyre via a tube. - Jack Luke / Our MediaWhen the clutch is disengaged, Gravaa says the system adds zero watts of friction. In theory, the only penalty will be the weight of the system fitted to the bike.Now spotted at Eurobike 2024 rigged up to a Reserve 40/44 gravel wheelset fitted with 700 x 38c Vittoria Terreno Dry gravel tyres, Gravaa says it's been hard at work to develop a system for gravel.Luijbregts said the gravel version of the KAPS system can inflate a gravel tyre by around 1.2 BAR / 17.5 PSI per kilometre of riding, although the specific test conditions (such as tyre size) werent confirmed.The system can inflate a gravel tyre by around 17.5 psi per kilometre of riding. - Jack Luke / Our MediaAccording to testing, Luijbregts claims riders pay a 2-5 watt penalty as the system engages [to inflate the tyre].Over a 200-mile gravel course (such as Unbound), Gravaa claims a 72kg rider would see a 21w normalised power benefit, and finish 28 minutes faster having carried out an estimated 80-100 tyre pressure changes en route.The system we have spy shots of isnt the finished article. Were told that the system consumers will receive will look very similar, but carry a few changes to help optimise the design.Whats changing?The hubs use special disc brakes produced by Galfer. - Jack Luke / Our MediaThe previous systems hub used seven bolts to mount a disc rotor. The new version is set to use five to save internal space inside the hub. Gravaa says consumer units will also have potted electronics inside, whereby the electronics are set into an epoxy resin. This, its claimed, will improve protection from moisture, dust and temperature fluctuations.Production models will use Classified shifters. - Jack Luke / Our MediaAffini used prototype remote controls when he tested the system 2023. Production models will use Classified shifters, the brand behind the Powershift hub system. Luijbregts also says that Gravaa has been hard at work developing a new app for the KAPS device, designed to make setup easier and to provide greater customisation of the inflation and deflation intervals.Luijbregts suggested high-level and professional riders may prefer to set up the system with smaller jumps in pressure, while others may benefit from larger intervals.The valve is patented. - Jack Luke / Our MediaA new valve has also been developed something Gravaa admits couldnt be achieved without calling in specific expertise. The patented design uses a hydrophobic seal which allows air in and out, but keeps sealant in the tyre and prevents it from congealing around the inlet or entering the KAPS system.Connectivity is also set to spread to Garmin and Wahoo bike computers, opening the theoretical possibility of GPS-driven automatic tyre pressure adjustment although Gravaa says thats not on the cards for now, describing it as an unfair advantage, presumably given the UCIs regulations governing rider controls.Availability in 2024 and 2025The gravel KAPS system is set to be available later this year. - Jack Luke / Our MediaWhile exact timings are unclear, Gravaa says that gravel KAPS is set to be available later in 2024. A road version (like the one Affini tested) should come to market in early 2025.When the gravel system launches, were told that Reserve will be a lead partner of the system on its wheels, while DT Swiss is also set to feature KAPS on one of its wheelsets.Reserve wheelsets with KAPS are set to cost around 4,000, while the DT Swiss wheelset is likely to cost in the region of 3,300-3,400.Theres no word on how much complete bikes with KAPS will cost, but we were informed they would be towards the top end of price ranges.