Speaker 1: Zipp have just launched their second headline-grabbing wheelset for 2020. This
is an all-new 303 Firecrest Disc Brake Wheelset. When I say all-new, I think it literally is
all new. This represents a big shift for the brand. They're saying, that in comparison
to its predecessor, this wheelset can save you between 10 and 50 watts at 40k's an hour
which admittedly sounds extraordinary, but let's be clear this is not just claims about
aerodynamics. This is about tire dynamics as well. How it works with the wheelset as
a whole. Something Zipp are calling total system efficiency. In this video we're going
to explain exactly what that means and how to get those efficiency savings.
[music] When we first started talking about tire pressure
here on GCN back in 2013, most road riders typically ran between about 90 and 120psi.
Now as the years have gone by those pressures have decreased. Why? Well, tires have got
wider. They've gone from 23s to 25s to 28s and beyond and that's allowed us to run lower
pressure without fear of puncturing and improve our comfort.
However, it's not quite as simple as that because research has shown in recent years
that actually a tire with lower pressure passes on less vibration from the road onto the bike
and into the rider which allows you to roll way, way more efficiently, yes, saving upwards
of 50 watts on really rough roads. A few years back we even unwittingly did a test of our
own on the cobbles of Paris–Roubaix and showed exactly that.
Which bike is faster over Paris–Roubaix, a road bike with 28 mil tires, a gravel/cyclocross
bike with 35-millimeter tires, or a mountain bike with 54-millimeter wide tires? By quite
some margin even though it has the aerodynamics of a bus it was the mountain bike, with the
cyclocross bike 5 seconds behind and a further 5 seconds back to the road bike.
The mountain bike felt slower what with the high-front end and the massive handlebars,
but it went faster, why? Well, suspension, but massive soft tires isolating us from the
vibration and allowing us to roll faster. What's this got to do with the new Zipp wheels
then? Zipp say that their engineers have also had their thinking caps on and have been putting
considerable time and energy into researching efficiency. They've been doing so using an
aero stick which is a device that sits on the front of the bike and can accurately measure
your aerodynamic drag. From that, you can then extrapolate out what proportion of your
total power output must, therefore, be coming from rolling resistance.
They have also modified a rolling road, to make it perhaps the most uncomfortable rolling
road on earth, but one that you would imagine is a remarkably good simulation of Belgium.
It would be like the rolling road Spring Classics Edition. Ultimately, they've backed up those
previous test results and they've done so with some really solid data. It shows, in
a nutshell, that your optimal tire pressure is a balance between rolling efficiency and
damping efficiency. A hardier tire rolls more efficiently because it deflects less and that
deflection costs energy. However, it also transmits more vibration to the bike and to
you, the rider. That vibration also costs energy and a lot more in fact than people
realized. Now if you plot that data on a graph, then
you get a bell-shaped curve. You see that if you have too soft a tire, then you've got
to put out a lot of watts because it's really dragging. Too harder tire and you also need
to put out a lot of watts because it's really draggy, but for different reasons. The exact
position of that optimal point, and indeed the shape of the curve, depends on the rider
weight and also the surface that you're riding on. The rougher the surface, particularly
terrible roads and off-road, the bigger the potential savings you can make. That is where
that carrot of a potential 50-watt saving comes from.
With all of this data, Zipp have designed a wheelset that forces you to run wider, more
efficient, tires. You need to run tubeless tires on here. They've optimized the whole
thing, not only for aerodynamics but also designed it to allow you to run super low
pressures. The first, perhaps the most significant thing is that they've increased the width
of the rim bed to 25 millimeters. The old Firecrest was 21, the 303S that was launched
a few weeks back is 23. This one then, the widest of the lot, at 25. Why the increase
width over the 303S? Well, Zipp say that they recognize that some customers might still
want to run 25-millimeter tires, and so the 303S allows that.
With this one, it's really important to note that that rim bed is so wide, you cannot use
narrower than a 28 on there. You can see when you look at it that actually the shape of
the tire on this rim is very different to normal. You have these much straighter sidewalls
that firstly improve your aerodynamics, but that also, crucially, supposedly, give the
tire more support so that you can run lower pressures than you ordinarily would but still
corner without the bike feeling squirmy. [music]
Now, how low you need to go depends as we've already heard of course on your body weight
and on the surface of the road or trail that you're riding on. Handily Zipp have packaged
up all of their data and put it into an online tire pressure calculator. That takes into
consideration, not just the fundamentals that we've already talked about, but other things
like tire width, rim width even tire type. Anyway for me with this setup so 28 mil wide
tire, it's suggesting that I run at 59.1 psi upfront and 62.9 psi in the rear tire. That's
about 4.0 and 4.3 bar. Were I 10 kilos heavier it would be suggesting about 4 psi more, front
and back, so that would be then about 83 kilos. Ah, 59 again, ah, 60.5, it's hard to get that
0.1. Now at this point, many of you might be thinking
that some wheel brands have been running 25 mil rim beds for a while now and you'd be
right but what gets interesting here is that Zipp say this is about more than just tire
pressure because they're actually designing, they say, compliance and vibration damping
into the rims themselves. Now to her dyed-in-the-wool roady, this might sound a bit weird because
stiff wheels have been considered good wheels for about as long as I can remember, but I'll
whisper it, "Mountain bikers have been onto compliance for a while now, and actually Zipp
focused on it when they designed their 3ZERO Moto Wheels recently." While I hate to admit
it, mountain bikers might actually be able to take the credit for this one.
Now, what does 'compliant' actually mean though? Well, it means that a wheel can deflect energy
away from the bike basically. Rather than passing all the vibration and impacts from
the rim and through the spokes, some of it can dissipate elsewhere. However, as you're
probably familiar with, on frame design by now, the beauty of carbon-fiber means that
you can still design in lateral rigidity so the wheel doesn't feel flexi when riding out
a saddle. Now how do you design a compliant rim? Well,
Zipp say different layout, different resin, basically, everything is different on this
new rim. Not just a new rim but new hubs too. Now just a quick aside here actually, arguably
of as much significance in the redesign is the fact that these wheels have shared a whole
load of weight compared to their predecessor. They're now just 1,355 grams for the pair
which is really, really light. Plus the redesign has also allowed Zipp to refine their production
process, improve the efficiency of it, and then that's reflected in the price. These
are considerably more affordable than their predecessors. They're now just €1,800 for
the pair, plus they also have that lifetime replacement policy that we talked about with
the 303S's, that means that you will get a new pair of wheels if anything happens to
these whilst you're out riding. Now just sticking with that last point there
about something happening to your wheels whilst out riding, I think a lot of us run or ran
higher pressures on our tires for fear of hitting stuff when out on the road like potholes
and things, you either get an impact puncture or worse, if you hit it hard enough, you could
dent or crack your rim. What happens then if you hit a pothole like this one, not exactly
a wheel eater, but still pretty significant, when you're running only 59.1 psi in your
tires. Of course, I'm not going to get a puncture here because I've got no inner tubes, I'm
running this tubeless, but how much support does a 28 mil tire from that wider rim?
Only one way to find out. Jeronimo. Well, I'd still recommend either avoiding it or
bunny-hopping it but I didn't hit the rim which I thought I would have done. Now, one
final point I thought I'd mention, was that when the 303S was launched a couple of weeks
back, it was claimed that it was significantly more efficient even than the old 303 Firecrest.
Now then, how do these two stack-up? the 303S and the new 303 Firecrest? Apparently, this
one is 5 watts more efficient at 40 kilometers per hour. That, I guess, is either a lot or
a little depending on what type of rider you are.
The differences, of course, are that rim width but also the rim profile is different. These
are actually shallower than they ever have been. These are 40 millimeters deep now as
opposed to 45 millimeters deep for the 303S. That is your new 303 Firecrest from Zipp,
but also a whole load of data that adds fuel on that fire of why the tires can be faster,
why they can be more efficient. Perhaps, then all of us should be running 28s and above,
certainly, if we live in the real-world and we're riding on pristine tarmac.
Anyway, make sure you let us know in the comments section that what you think about this. What
width tires do you already use and would you be tempted to drop to super-low pressures
like this? Get involved in the comments section and please, give this video a big thumbs up
if you've liked it. [00:11:20] [END OF AUDIO]