– Deep section wheels, they look bling, they make a cool swooshing noise but most importantly
they offer a significant aerodynamic benefit over a
standard shallow box section rim. But many people are
worried about riding them in cross winds and for good reason. When they suddenly catch the wind and unexpectedly twist the
handlebars it can feel scary. In some cases downright dangerous. But, just how bad a problem is it? In this video we’re gonna look at deep section wheels verses cross winds. (dramatic music) We’re using some of Zip’s
range of wheels to illustrate this, because they’re one of our sponsors. But also, because they’ve
actually spent huge amounts of resources in tryin to develop wheels that are easier to handle
in really windy conditions. But, many of the points in this video apply to other wheel brands too. One of the reasons why
we’re tackling this subject is because disc brakes
are encouraging people to use carbon wheels more often. If you ride rim brakes
in well, dirty roads like what we have today,
then you can trash you carbon winds quite easily. But, if you remove that, then
there’s no real disincentive not to use carbon wheels all year apart from the initial outlay. With that considered, if your go to wheel is a deep section wheel then you wanna be able
to run it all the time. So, the question is, can you? (upbeat music) Fundamentally, deep section
wheels can feel more unstable because they present a larger
surface area to the wind. Now, this is worse on the
front than it is on the back because the front wheel can turn. ( percussion music) It’s first important to
understand what makes a deep section wheel feel unstable. So, here is some science. As you ride the tire is the leading edge and this splits the air. The rim then controls the airflow helping it to smoothly come together at the trailing edge behind the rim. Now, the idea here is
that this reduces drag but makes you faster for the same effort. Now this tends to work fine when the wind is at naught to one degree’s
of yaw, which means head-on. However, when your
angles start to increase such as in a crosswind,
problems can arise. At higher yaw angles the airflow can suddenly detach from the rim. This causes a sudden drop in pressure and turbulence forming in an area of low-pressure behind the rim effectively sucks it
backwards which is not ideal. And this kind of aerodynamic stall is a similar concept to
that in airplane wings. Except the difference is that, when an airplane wing
stalls it falls out the sky. When a wheel stalls you feel that twitch or the sensation of it catching the wind. This is disconcerting,
potentially dangerous and it slows you down. This isn’t my time trial bike
but use your imagination. In my experience in riding time trials with a deep section front
wheel, whenever I felt instability because of the wind I’d often find myself
coming off my tri bars and subsequently becoming less aero. It doesn’t have to be a big gust either. Little twitches here and
there can momentarily cause you to soft pedal and
in some cases even free wheel. On a windy day these little twitchy events can actually be very frequent and add up to a
significant amount of time. Perhaps the worst thing that can happen is you will get blown
off your bike entirely. Now, admittedly this isn’t
very common but it can happen. Famously Geraint Thomas,
the Tour de France champion, was blown off his bike
in Gent-Wevelgem in 2015. It can also mean that in windy conditions a deep section wheel
isn’t necessarily faster than a shallow one and can
in actual fact be slower. Plus it’s kind of nice
not having the sensation that you’re gonna get blown
off your bike at any moment. Although deep section wheels
can be twitchy in the wind it’s not as bad a problem
as you might think. Now, for reference,
I’m around 70 kilograms and would ride a mid depth
40 to 60 millimeter wheel all year round. Now the reason for this is primarily aero gains because well
I’m all about the aero and need all the help I can get. But also, because it’s manageable. Wheel design has improved so
much over the last few years that they’re much easier to ride than the older V shaped design. Back in the day when deep
sections first started to appear, they had a V section profile. Now this was really good
at naught degrees yaw but not as aerodynamic
at other yaw angles. Yaw being the engineering term
for the angle of the wind. Whoa whoa, what are yo doing? It was only in the 2000’s you can lose the black and
white and the flack cap. (trumpet wah wah wah) In reality when your
riding in the real world, the yaw angle of the
wind is very rarely zero, meaning head-on. It’s often coming from all
different angles all around you and it’s constantly changing. Fortunately wheel designers realize this and started to design rims accordingly. Not all rims are created equal. The next big step in the
evolution of deep sections wheels was the use of wider and
rounded toroidal shape rims. Now in 1996 a patent
co-owned by Head and Zipp allowed for toroidal rim sections which in non-maths geekery
terms, is well, U shaped. Most wheel brands went on
to adopt similar shapes owing to it being more
aerodynamically stable and less prone to crosswinds because it allows the
higher angles of stall. Over the last 20 years or
so the toroidal rim profile has been tweaked and honed to improve it incrementally in the crosswinds. That has led us to these, hyper foils. The idea here is that the multiple bumps or nodes on the 454 but also the 858 allow multiple locations for
high frequency vortex shedding. What on earth is that, I hear you ask. Well. In simple terms, rather than
let the pressure build up and then dump all that
air in one big stall, which would cause a massive twitch, the wheel is said to be constantly dumping smaller amounts of air
in sort of micro-stalls. Now according to Zipp this
makes the wheel much easier to handle yet still
retaining the equivalent straight line speed. The theory is that you can ride more deep wheels more of the time. Interesting. Should you get a pair of deep section rims and if so, what depth should you go for. Well ultimately it
comes down to your needs and what you want them for. We’re not for one second suggesting that you have to get a
pair of deep’s either. There’s nothing wrong with a standard aluminum box section rim. But, you can rest assured that with advancements in design,
deep section wheels have become a lot easier and
safer to handle in crosswinds when you can run them,
potentially, all year round. However, we should still point out, they can still be more of a handful, although much improved,
than a shallow rim. If I was selecting a wheel for time trials then I’d go for a deep 70
to 80 millimeter front wheel on, well, all but the windiest of days. However, if I was only gonna own one set of deep section wheels,
then I’d go for a mid-depth around 40 to 50 millimeters. This is because this is a
depth I know that I feel comfortable riding pretty
much all of the time and if it was too windy
to ride that kind of wheel I feel that, well, it would
be too windy to ride full stop irrespective of the wheels you are riding. It’s also a really versatile depth whereas something like the 858, although it’s very fast, is
a little more specialized. There is a caveat though. Now while I’m comfortable
riding a 303 or a 404 depth wheel in most conditions, smaller lighter riders can
suffer in crosswinds more. So if your diminutive
you may want to consider getting a shallower wheel
especially at the front. At the front you have
less weight over the wheel to stop it twitching. Also, if you happen to live
in the windiest place on earth then well, plan on riding lots there, then you may also want
to get shallower wheels. Incidentally the windiest
place on earth is, well it’s Mt. Everest, I fact checked it. Hope you found this video
useful and informative. If you have, give it a thumbs up. If you’d like to watch another video I highly recommend this one where Si see’s just how fast aero wheels can be. It’s down here.