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Zipp’s new 303-S aero carbon road wheels mark a dramatic new direction for the brand’s best-known model. Whereas the 303 has primarily been focused narrowly on road racing for much of its existence, this latest 303-S is now aimed more at the way more modern drop-bar bikes are being ridden — with rougher roads, wider tires, and less of a focus on traditional forms of competition.
Rim depth remains the same at 45 mm, but the width has ballooned, both inside and out. External width has grown a fairly modest 2 mm to 27 mm at its widest point, but the internal width is now a very healthy 23mm — a leap of 6 mm over its predecessor. Tubeless compatibility is baked in, and Zipp has also adopted a hookless internal profile.
This hookless aspect is critical in a number of ways. On the one hand, it’s easier to manufacture (which helps in the 303-S’s lower cost relative to previous 303 models). However, it’s also more impact resistant, which is especially important given the 303-S’s expanded mission and the lower intended inflation pressures, as well as the far more comprehensive lifetime warranty.
Those lower inflation pressures aren’t just something Zipp will be recommending for ride quality, either; officially, the maximum allowable pressure is now just 72.2 psi, or five bars. Furthermore, Zipp doesn’t plan to publish a list of approved tubeless tires.
“Our line of communication is that all tubeless or tubeless-ready tires are compatible with our new rims, except those from manufacturers who are explicitly prohibiting hookless rims,” explained Zipp global product manager Bastien Donzé. “At this point, there are still several major tire makers who claim they are not compatible with hookless rims. They think that ETRTO [one of the international guidelines governing rim design — Ed.] does not allow hookless, which we don’t believe is correct. Hookless is okay there, as long as tire pressures do not exceed 5 bars / 72.5 psi. Interestingly, all our testing shows that tubeless is most efficient (meaning faster) on wide rims at pressures below 70 psi. I’m running 60 psi in 28mm myself, for instance.
“So for us, the 5 bars max pressure is not a question of safety; it’s a question of performance. In this case, lower pressure truly is faster, especially as the roads become rougher. The challenge we’re facing is that we need to let users know they really shouldn’t run their usual tire pressures on wide rims, or their experience will be terrible, and they won’t benefit from our Total System Efficiency story.”
Aerodynamics is still important — this is Zipp, after all — and the company says the updated shape is now optimized around tires with a 28 mm measured width (which, in many cases, will mean road tires with a 25 mm printed width).
In yet another sign of the changing times, Zipp is offering the 303-S exclusively for use with disc brakes. According to parent company SRAM, OEM sales have shifted almost entirely to disc brakes in the last couple of years, and that trend isn’t likely to reverse itself. Zipp will likely still continue to offer wheels for rim brakes at the upper end, but the #savetherimbrake crowd should consider this yet another nail in the coffin.
The new 303-S rims are laced to Zipp’s 76/176 front/rear hubs with 24 Sapim CX-Sprint bladed stainless steel spokes in a two-cross pattern. Zipp is using brass nipples here, which are admittedly heavier than aluminum ones, but it’s a minor concession given how few spokes are used here. And on the plus side, brass is stronger and more corrosion-resistant than aluminum, too, which is particularly noteworthy given how likely it is that these wheels will be used tubeless.
Buyers have their choice of Shimano HG/SRAM or SRAM XDR freehub bodies. Campagnolo bodies are also available aftermarket, but Center Lock splined rotor interfaces are standard across the board, as are 12×100 mm and 12 x 142 mm thru-axle end caps front and rear.
Claimed weight for the set is 1,525 g (710 g front; 815 g rear), and retail price is US$1,300 / AU$2,229 / £985 / €1,100, including tubeless tape, tubeless valve stems, and rotor lockrings.