The Zipp 303 road wheels just got a massive overhaul. They’re wider, with a new hookless rim. They’re aerodynamically optimized for 28mm tires, and designed to let you run lower air pressure. Separately, these are all good things.
Add it up, and Zipp says you’ll have a faster wheel no matter how rough the surface. Here’s how it all comes together…
How the Zipp 303 got here
The 303 series has long been Zipp’s all ’rounder, being tasked with everything from the classics on cobbles, smooth fondos, cyclocross races, and more recently gravel bikes. The mid-depth 45mm rims hit the sweet spot in aerodynamics and weight for most types of riding.
It’s been a while since they’ve been updated. The 303 got a tubeless version in 2016, which was a little late compared to some other wheel makers.
Now, they’re getting a major update to modernize the profile for wider tires, optimized for tubeless and disc brakes.
What’s new about the Zipp 303 rims?
A lot. They’re still 45mm deep, but that’s about the only carry over feature. These wheels have a new construction that helped bring the price down. Retail is now just $1,300 for the pair.
The rim is 2mm wider externally, pushing it out to 27mm. The important measurement is internal. By getting rid of the bead hooks, they increased inside width by 7mm. The new Zipp 303 S internal rim width is 23mm.
The new, wider rim profile is optimized for 700x28mm wide tires. And it’s optimized in several ways. First, aerodynamics. They say by removing the bead hooks, and not having to worry about a brake track, they could really smooth the transition from the tire to the rim.
And the wider rim better matches a wider tire’s frontal profile. Combined, it smooths the air flow and reduces drag when running wider tires.. But aerodynamics is only one quarter of the story…
Whatcha gonna do with all that space?
It’s one thing to just make a rim wider and say you can run wider tires on it. But Zipp had a lot of reasons to make the change. Besides helping to keep them relevant, it was really about making their pro riders faster on the cobbles and rough classics.
Their design and feature set had to evolve as gravel and all-road bikes have become more popular. It used to be all about aerodynamics, with a focus on wind tunnel testing, 40k TT performance and just plain beating the wind. Now, they have a four-pronged approach where efficiency equals speed, not just aerodynamics
For them, efficiency means beating wind, gravity, rolling resistance and vibration losses.
We covered wind. And gravity simply means reducing weight. The new 303 S wheels are 155g lighter at the rims (77.5g per rim) than the 302 Disc Brake wheelset they replace.
Rolling resistance and vibration reduction go hand in hand, so we’ll cover them together. By opening up space inside, and making the rims tubeless specific, they allow you to do two things: Run wider tires that are properly spread out on the rim, and run them at lower pressures.
This means that a wider rim that pushes the tire wider will create a wider, but shorter, contact patch with the ground. The effect is that there’s less “tire sag”, which is how much of your tire sidewall is compressed where it meets the ground.
A wider tire won’t sag as much, so there’s not as much sidewall deformation, which means less friction and resistance. The result is improved rolling resistance efficiency. It also “looks” like it has more grip because of the fatter patch, but, technically, the actual contact patch size would the be the same…and they don’t measure for that.
Good, Good, Good…bye, Vibrations
Vibration Losses is a new metric for Zipp, and they had to build new testing equipment to measure it. They started by testing on cobbles, and the pros broke every prototype. But it was the beginning of making something that could stand up to any type of terrain.
The idea is to measure whole body vibration, then reduce it. With the current 2020 Zipp 303 wheels’ 21mm internal width, you have a narrower tire volume with higher pressure and rough terrain would transmit basically everything to the rider. As if to state the obvious, spreading that same tire size out and reducing the pressure reduces how much of that vibration makes it to the rider. Thus there’s less power lost to vibration, the more comfortable the rider is, and the faster they can go.
How d’ya like them Apples to Apples?
This is important: The comparisons in contact patch and sidewall compression above are based on using the same size tire at the same tire pressure. They’re to illustrate the benefits of a wider rim when you want to run lower tire pressure. Trying to run lower pressures on a narrower rim won’t get the same results because they’re less volume to cushion the ride.
You’ll always have a tradeoff between support and reducing vibration and rolling resistance. Within a logical range, lower tire pressures will reduce both and help you ride faster. But the tire’s sidewall will compress more as you lower the pressure, eventually feeling squirmy and losing it’s ability to cushion against bumps.
Zipp says the chart above is their recommended starting points, then it’s up to you to play around with different pressures.
What’s the max tire pressure? Rider weight limits?
Max tire pressure is 72.5psi (5bar), and that’s with Tubeless or Tubeless-Ready tires ONLY. You can run tubes inside if you need to, but they say you need to run tubeless/TR tires because those tires have the stiffer bead necessary to work on a hookless rim design.
Rider weight limit is the same as all their other wheels: 250lbs (115kg).
They recommend a minimum tire size of 700×25, and maximum of 700×55. There is no 650B size offered in this wheelset.
2021 Zipp 303 S Specs, Pricing & Other Trivia
Technically, this wheelset is the successor to the 302 Disc Brake wheelset. And it’s 155g lighter than the 302 Disc, with the weight savings coming almost exclusively from the rims! That means a lot less rotational weight, despite the wider rims, and at a lower cost. Not bad, eh? They use Zipp’s 76/176 hubs with Center Lock brake interface and include the rotor lock ring.
Notice anything different? The graphics are a new logo and look for Zipp. We first saw this logo on their 3Zero MOTO Mountain bike wheels, and you’ll now see it moving across their road line, too. They’re permanent, meaning they’re not decals, which makes them a bit sleeker and saves a few grams.
Zipp 303 S actual weights
The wheels come pre-taped for tubeless, and weights without valve stems are 717g front and 828g rear (1,545g total…right on target). Add two valve stems and the rotor lock rings and you gain 27g (13.5g per wheel).
Notice anything missing? Dimples. Which, along with the lower price point and lack of a Firecrest or NSW icon, suggests that there’s more to come with this new, wider rim profile. Stay tuned…
