Before I’ve even slotted them into a bike, the first test of any tubeless wheelset is how easy and hassle-free it is to get the tyres seated and inflated.
My experience with tubeless tyre fitting, in general, is it can still sometimes be a bit hit and miss, depending on even the tiniest variations in tolerances. Some rim/tyre combos just go straight up, others need a lot more persuasion.
But having set the Zipp 303 S wheels up with a variety of both road and gravel tyres – starting with Zipp’s own offerings in both cases but also competitor brands such as Michelin, WTB and Vittoria – every time tyre fitting and inflation was a cinch.
I didn’t even need to turn on the air compressor. A standard track pump was fine, each time.
I rode the Zipp 303 S wheels both on and off road and they performed admirably across both disciplines, but in terms of performance attributes it was easier to examine those and try to quantify any gains on the tarmac, so this is where I shall focus my thoughts.
In ‘road mode’ Zipp’s own Tangente R28 tubeless tyres were my preferred option, as the profile the tyre had once inflated clearly made the best of the rim dimensions (as Zipp had based its own testing around this tyre width), in terms of appearing perfectly rounded and with the sought-after parallel sidewalls and almost seamless transition from tyre to rim.
Checking with a Vernier calliper revealed a 28mm tyre measured just under 30.7mm inflated to 55psi, so clearly the rim’s 23mm internal width was having a significant widening effect on the overall tyre volume, as Zipp promised.
This was the pressure I was using whilst testing these wheels (on the road), as per Zipp’s own recommendations for my body weight (66kg) with 28mm tyres. The recommendation is actually 53/57 psi, but I split the difference.
That’s not far off half the pressure I would have been using just a few years ago, and even a good 20psi lower than what I have regularly been using recently.
I don’t have a wind tunnel or test lab in my garage at home but I do have over 20 years of elite level racing under my belt from which I have years of performance data based on my most regularly ridden training routes, for which I know intimately every single crease in the tarmac.
As such I can fairly accurately tell, quite quickly, what kind of shape I’m in based on riding these routes, and keeping track of a number of key data. From that I am able to form fairly informed conclusions about the likely extent to which certain equipment might be having any causal effect on my performance – for better or worse.
So here’s the thing. I know, thanks to the current lockdown, and an increase in the number of turbo sessions I’ve been doing lately, that my power numbers aren’t great during the time I’ve been testing the Zipp 303 S wheels.
Yet every ride I did on the 303 S – on a standard road bike (not aero) – I was coming back with impressively fast ride times, indeed times measurable in minutes, not seconds, quicker than I’d done in a good while.
I trawled my ride data thoroughly. Yes, some days I might have put it down to having favourable winds for certain portions of the routes and others just very little or no wind at all but there was nothing, beyond using these wheels and with tyres at such low pressures, that stood out to convince me as to why I might be faster, despite my legs putting out less oomph.
I’m not going to get into the point about wider tyres having less rolling resistance. That point I think now is well-established and beyond doubt, but there’s more to this than that alone.
What is clear, then, is there is no reason to suggest that Zipp is leading us up the garden path with this whole super-low tyre pressure thing. Far from. Never did I feel like the tyres at 55psi were squidgy and draggy.
The sizeable drop in tyre pressure was almost imperceptible – speed wise – which was a pleasant surprise, although that said there were a few moments when attacking a steep incline out of the saddle I could definitely sense the front tyre bouncing a little, but that didn’t seem to have any negative impact on my climbing speed.
I did however notice that considerable amount more comfort the wide/soft tyres delivered throughout my rides. And speed and comfort aren’t mutually exclusive attributes. One clearly influences the other.
And, herein lies the secret. I think. We can certainly hypothesise that wider, softer tyres act as a suspension system isolating us from so much more of the bumps and road buzz, reducing considerable amounts of wasted muscular energy that is used to stabilise our bodies against the constant pounding forces.
At the same time one could also speculate that if we are able to ride more smoothly, our power delivery could be more efficient too. And those factors cannot be undervalued.
Certainly the latter is far easier to judge and/or measure, so the jury’s still out on the former at this time, as the evidence is somewhat equivocal, but it definitely stacks up as a convincing argument.
So, such low tyre pressures might seem counterintuitive to delivering speed, but the evidence I have from my tests suggests that not to be the case at all.
With the 303 S’s modern rim shape, low weight, and a previously unheard of (for road) 55psi in tubeless 28mm tyres, I can say, the result is these wheels are undeniably fast. Believe the hype. It works. For under a grand, too.
I can’t really fault the 303 S: This wheelset has looks and performance attributes well beyond its price tag.
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