In keeping with current bike trends, Zipp has created a 650b version of the 303 Firecrest wheelset, which is naturally tubeless-ready and for disc brakes only.
The emergence of road-plus and gravel bikes, with tyre widths from 28mm to 50mm, has increased the need for smaller-diameter wheels. That’s because a high-volume tyre on a 650b wheel has roughly the same overall diameter as a 700c wheel, but offers incredible grip, comfort and versatility.
Smaller-diameter wheels fitted to an appropriately scaled bike are helpful for shorter or younger riders too, permitting equivalent handling and performance to a larger machine.
Designed for tyres sized 28mm and larger, the 303 650b rims have a new carbon-fibre layup and are 21mm wide internally with ridges that lock a tubeless tyre’s bead in place so it remains secure at low pressures.
They’re 45mm tall, with the blunt-nosed shape measuring 28.9mm at their widest point externally. Zipp’s ABLC (Aerodynamic Boundary Layer Control) dimple pattern is moulded in to the rim all the way to the tyre for improved aerodynamics, especially at yaw angles of 10 to 20 degrees that, Zipp says, you face over 50 percent of the time.
I weighed my pair, including the factory-installed tubeless rim tape and valves, plus thru-axle end caps, at 1,525g, which is good for reasonably deep tubeless wheels.
Also included are exchangeable end caps for 15mm front, and 12mm front and rear, as well as quick-release skewers and a valve tool. The 77D and 177D hubs feature 17mm axles, and come with a standard freehub body, but will also accept SRAM’s XDR driver body for 10-42 cassettes. They’re built with 24 Sapim CX-Sprint straight-pull spokes, have external nipples and a rider weight limit of 250lbs/113kg.
My first experience of the 303 650b wheelset came at the Roc D’Azur’s new Gravel Roc race, using many of the same tracks as the mountain-bike event in the coastal hills near Frejus in the south of France.
With 47mm wide, almost slick tyres fitted, and nearly 3hrs of dusty, rocky trails, heaps of climbing and even a beach on the course, the Zipps took a sound thrashing and didn’t miss a beat.
More recently they’ve proved their mettle on British singletrack and gravel, with 2.1in Maxxis Aspen tyres, which seated very easily and remained secure throughout, even when running at 20psi.
Repeated accelerations out of corners and short, sharp climbs tested the stiff, small wheels’ credentials, and they performed superbly well, their low mass really helping slow-speed getaways.
Their extra depth is ideal on sustained high-speed sections and keeps the spokes shorter for a taut feel. The 303 650b Firecrest wheelset is responsive, fast, reliable, light and robust, and more than capable of taking you anywhere in style. But sadly, it’s not cheap.
Zipp 303 Firecrest 650b tubeless disc wheel specifications
Width (internal): 21mm
No. spokes: 24
Spokes: Sapim CX-Sprint straight-pull
Price Front: £1,071 / $1,150 / AU$1,655
Price Rear: £1,249 / $1,350 / AU$1,944