RCX Ultralight

RCX Ultralight Rims

The RCX Ultralight series wheels are some of the lightest carbon road wheelsets on the consumer market. Each model has been individually UCI certified. One of the primary reasons for the lightweight construction is our advanced carbon layup. Our lightweight rims offer extremely low inertia, significantly improving acceleration. RCX Ultralight wheels have been tested to be 13% more compliant than GCX Ultralight wheels, offering a more comfortable ride.They are raced by our sponsored UCI pro cycling teams, Victoire Hiroshima and Citymesh - Customm and will be ridden in 9 UCI WorldTour races in 2026.

The rims feature 21mm inner widths and 31mm outer widths, which make them aerodynamically and structurally optimized for 28c tires. As a result, they outperform wider rims in terms of optimal rolling resistance, grip, comfort, and handling. The rims have modern u-shaped profiles, giving them improved stability when descending and in crosswinds.

In order to compensate for the additional weight of the valve on tubeless and inner tube setups, we have added carbon fiber to the rim directly opposite of it in order to balance the wheel, creating a smoother ride.

Despite their light weight, RCX Ultralight series wheels can withstand 2.5x theUCI Vertical Impact Test standard.Tubeless tape comes pre-installed. Tubeless valves and two spare carbon spokes are included in the box.

Decals are laser engraved, giving the wheels a unique look while saving additional weight. Learn more about laser engraving here.

See here for more information on the difference between Ultralight, Light, and Team version wheels.See why we chose 21mm inner widths.

Rim Profiles

Precision Ratchet Hubs

At Particle, we try to avoid marketing trends and tech that don’t offer real world performance gains. For this reason, we have chosen to use the gold standard of hub design, the star ratchet. We now offer two different hubs, the SR1 and the AR1.

AR1 hubs are used on our base configuration. They come with 36T, 45T, and 54T ratchet options as well as the choice between S&S ceramic or steel bearings. We recommend 36T ratchets for lower rolling resistance and improved longevity.

SR1 hubs use aerospace aluminum alloy, lower friction ratchets, and TPI ceramic bearings with tighter tolerances and better sealing than those from S&S, allowing for longer lifespans. SR1 hubs comes with 36T ratchets only and are only available with 4th gen carbon spokes.

Both hubs have 0.005mm and 0.003mm machining tolerances respectively, making them the most precise hubs available, lowering rolling resistance and improving bearing longevity. They use labyrinth seals and double layer contamination barriers, protecting bearings and ratchets from the elements.

Servicing is simple, as no tools are required. Star ratchets are also simple to clean and replace.

Carbon Spokes

In order to push the limits of what a performance wheelset can be, RCX Ultralight wheels come with both 3rd generation (AR1 hubs only) and 4th generation spokes replaceable carbon spokes. 3rd gen and 4th gen spokes weigh just 3.5 and 2.1 grams respectively including nipples. Our 5.2mm 3rd gen spokes offer the best when it comes to aerodynamics and lateral stiffness, while our 3.2mm 4th gen carbon spokes are the lightest spokes commercially available and offer a comfortable ride similar to steel spokes. Both spokes are less than 1mm thick. We have tested our wheels with 3rd gen carbon spokes to be 14% stiffer than those equipped with 4th gen ones. 4th gen spokes achieve such a low weight due to titanium spoke heads and threads as well as a new profile.

The hubs we have chosen have closed flanges, ensuring there is no risk of our spokes popping out, which is a concern on some carbon spoke wheelsets. Spokes are mechanically secured so they do not twist, ensuring they always stay in the most aerodynamic orientation. Our 4th gen carbon spokes offer significantly better compliance, giving you extra comfort with a weight reduction of 55 grams.

Our carbon spokes have been thoroughly tested and can survive more than 4000 newtons of tension, as opposed to steel spokes, which break under loads of between 2600-3200 newtons. We even provide spare spokes in the box.

Steel and Ceramic Bearing Options

The RCX Ultralight series comes with either S&S or TPI bearings depending on the hub. Each front hub uses large 6803 bearings, improving durability, increasing longevity, and reducing rolling resistance. Each rear hub uses two 15267 bearings, and each freehub uses two 6802 bearings. Our bearings use mixed contact seals to protect them from contamination, improving longevity, while offering low rolling resistance.

SR1 and AR1 hubs comes both come with steel and ceramic options.

*Warning: Ceramic bearings by nature are more fragile and easily damaged if you accidentally ride into a pothole or off a curb.

For more information about steel vs ceramic bearings, please see this article.