AX-Lightness

Ultra 24T Extralite Hub Tubular Wheelset

When setting out to design the Ultra 24T Tubular Wheelset, AX-Lightness wanted to create the superlative climbing wheel: light, stiff, and safe. With a claimed weight of under 800 grams for the set, they, well, they succeeded. To put that into perspective, the newest iteration of the same wheels Quintana rode to an impossibly dominant victory in a time trial up Monte Grappa weigh 1,170 grams.

As far as climbing wheels go, the rims follow a standard, low rotational mass formula. There are two peculiarities, though. The first is the 21.5 millimeter rim, which is wider than most super-skinny climbers. The extra millimeter of width allows for a more comfortable ride that corners better and produces less rolling resistance. The second is that AX-Lightness opts for a weave instead of the ubiquitous unidirectional fiber. While unidirectional fibers are preferable in situations where a component is bearing a static load, the dynamic load bearing properties of a fabric recommend it for a wheel, which rotates through various angles of load.

The Ultra 24Ts also benefit from AX-Lightness's Seamless Brake Surface, which uses high-pressure autoclaves to combine the wheels' layers with gas, eliminating any imperfections down to the smallest edge. The first curing cycle alone takes two and-a-half hours, which allows time to press out every pocket of air. This means the one-piece brake surface is both seamless and virtually free of imperfections, so there's no shuddering while braking during descents. While it may look like a typical, mass-production rim, the Ultra 24T is nearly perfect on a microscopic scale after its cured.

After curing, the wheels are tempered, which realigns the resin crystals to drastically increase the braking temperatures that they can withstand before the carbon softens and deforms. With this tempering cycle and virtually perfect curing, wheel failures are a thing of the past. The entire process takes almost eight hours — a time that's unheard of in today's industry but that you'll appreciate on long, fast descents.

The wheels' reliability is also boosted by Spoke Reinforcement Technology, which creates the spoke holes during the manufacturing process itself. There is no post-production drilling once the rims come out of the autoclave, so there's no additional structural weakness. As a result, the Ultra 24Ts can bear five tons of nipple resistance — again, these are built to be superlative. The wheels actually require special hubs so that AX-Lightness can tension the spokes to 1300 N, which is how they ship.

As you'd imagine, the hubs have to be something pretty special. AX-Lightness uses Extralite's Ultra Front SPM and Ultra Rear SPX Version 2.0 hubs, which maintain the superlative theme. The over-sized flanges are specially treated to self-align under spoke tensioning so they better handle the stress, and they also increase the spokes' stiffness, and therefore the lateral stiffness of the wheel. An oversized axle results in even less watt-losing flex, and the over-sized bearings complement the rims' low rotational mass by letting them spin up fast and hold momentum longer.

Please note that AX-Lightness recommends a rider weight limit of 220 lbs. (100kg).