Rueda trasera tubular Spinergy X-Aero Carbon 650c

The Spinergy X-Aero Carbon 650c Tubular Rear Wheel is a low-spoke-count aero wheel built around Spinergy's PBO fiber spoke technology, sized for the 650c bikes that were once a staple of triathlon and smaller-frame road setups. Instead of dozens of thin steel spokes, the X-Aero uses just 20 rear spokes molded from PBO composite fiber — a Zylon-type material made from tens of thousands of microscopic strands, rated at roughly three times the strength of stainless steel at half the weight. Spinergy shapes each spoke into a blade profile, which is how a 20-spoke wheel like this one is engineered to cut through the air with the drag of a conventional 32-spoke build.

That spoke reduction is the whole point of the design. Fewer spokes means less material fighting the wind at speed, and the bladed PBO fiber construction adds a degree of shock absorption that round steel spokes don't offer, which takes some of the sting out of rough pavement without the wheel feeling vague underneath you. It's the kind of wheel built for someone who wants a noticeably lighter, more aerodynamic rear wheel without stepping up to a full carbon disc or deep-section race wheel.

The 650c size is worth pausing on. It's a smaller-diameter wheel than the now-standard 700c, and for years it was the go-to choice for triathlon-specific frames and road bikes built for shorter riders, where the smaller wheel allowed for tighter frame geometry and a lower front end. Fewer new bikes are spec'd around 650c today, which makes a wheel like this most useful to riders who already own a 650c-compatible frame and want to upgrade or replace a wheel without hunting down a discontinued size. As a tubular wheel, it pairs with glued-on tubular tires rather than a clincher or tubeless tire — a setup racers have long favored for ride feel and weight, though it does mean budgeting for tubular tires and rim cement separately.

On the drivetrain side, the X-Aero rear wheel is built for Shimano and SRAM 10-speed cassettes, which puts it squarely in the era of bikes it's most likely to serve — a 650c tri or road bike running a 10-speed groupset that needs a lighter, more aerodynamic wheel without a full wheelset replacement. At its regular price of $895, the X-Aero sits with Spinergy's other composite-spoke wheels as a premium aero upgrade. At RA Cycles' current price of $129.99, it's a way to get that PBO fiber spoke design — and the aero and weight advantages that come with it — onto a 650c bike for a fraction of the original cost, whether as a primary wheel or a well-priced spare for a rider who already knows the platform.