By the time you're cycling at 30 kilometers per
hour, as much as 90 percent of the resistive force experienced comes from aerodynamic drag. And it's not until you get down to 12 kilometres per hour when rolling and air resistance are equal. While most bicycle travelers do not cycle at speeds above 20 kilometres per hour, we still ride in
places with headwinds, meaning the air resistance is the equivalent of cycling at much higher speeds.
Another way to frame it, you could cycle further with the same amount of effort, or you could cycle
the same distance, but have more energy left at the end of the day. Today, we're going to take a close
look at some interesting findings in the touring and bikepacking space, to find out how some small
changes might make our lives a little bit easier. But first, some ultra basic fluid mechanics. Feel
free to skip to 2:15 if you just want to see the results. Fluid mechanics is ultra-complex but
if we distil it down to the most basic elements relevant to bicycle touring, we end up with this drag equation. Drag consists of the air density, the speed of the rider, the frontal area of the rider, and the coefficient of drag. For touring, it's the frontal area and the coefficient of drag
- or Cd - that we are looking to optimize. The Cd describes how aerodynamic the shape of the object
is, and it's not a fixed value either. For example, it changes depending on our touring speed,
the surface textures of our bike and gear, and the air density. Here are some approximate
drag coefficients of different objects. And here are some rough drag coefficients of
different riding positions for you to compare. As you can see, without luggage you're probably
about as aerodynamic as a cube. When we multiply the coefficient of drag with the frontal area,
we get the CdA, or amount of drag per unit of area. To reduce our CdA, we can make our shape more
aerodynamic, our frontal area smaller, or both. To get the unified hour record, it is estimated that
a cyclist needs to have a CdA of 0.2, and you need a CdA 10 times less to get the recumbent hour
record. Five years ago, I was interested to find out what would happen if I adjusted the frontal area of my luggage setup. I conducted a test to find out the speed difference between bikepacking
bags, rear panniers, front panniers, and both. With a power meter fitted to my bike so that I could
pedal at exactly 200 watts, I cycled around a velodrome for a full day with different bag setups
so that I could create data that was statistically significant. With a higher than average touring
speed, two large front panniers were 6.4% slower than bickpacking bags, two
large rear panniers were 6.5% slower, and a complete pannier set was 7.9% slower. As
these speeds are much higher than most people travel, I would love to conduct this test again
at a speed between 20 and 25 kilometres per hour and I would also like to try it with a larger volume backpacking handlebar pack. Before we move on to the wind tunnel testing, check this out. This
is the biggest touring bike available overlaid on the smallest. I've just updated my touring and
backpacking bike buyers guides, and as part of the update, I've uploaded the frame geometry of hundreds
of different bikes for you to visualize on the website, Bike Insights. If you haven't already
seen them, my guides teach you everything about bikepacking and touring bikes before allowing you
to compare hundreds of different options available at the back of the book. The best part is that
these guides are updated yearly for free! Wind tunnels are commonly used to accurately compare
the aerodynamic properties of different objects. But one of the issues in the accuracy of the data
is that the wind arrives in a steady-state, whereas wind, when you're out cycling, is often much more turbulent. In addition, there is no ground speed in a wind tunnel, and the rider is locked into place,
which doesn't quite mimic the riding movements outside. A technology that might provide better
data for outside conditions is aero rakes, which are commonly used in Formula One. Back to wind
tunnels - even with the inaccuracies we can still learn information about how different luggage
setups are likely to affect your speed. Francis Cade made a luggage aero testing video and found
a less than 1% reduction in speed when he added two bottles to his fork. With a handlebar
bag attached as well, it reduced his speed by a bit over 2%. Then when he added a bickpacking
seat pack, it actually made him a touch faster, likely because the airflow was separating cleaner
behind his body. And the complete ensemble with panniers made him 3.6% slower, which works out
to be about 9 minutes over 100 kilometers. Specialized has a lot of wind tunnel videos
on their YouTube channel, and there are two interesting results relevant to touring. The first
is with regards to your hand position on a flat handlebar. Most people ride in the grips, but if you
can comfortably move your hands inwards near the stem and flatten your arms, that is worth a 6% gain in speed at 26 kilometres per hour. The second is the difference between baggy and
fitted cycling clothing. The numbers here suggest your choice of clothing is almost as important as
your luggage setup, which makes sense as your body makes up the largest percentage of your frontal
area, and the drag is higher on a flappy surface. Bicycle Quarterly has also tested different
bike and gear setups in a wind tunnel. At 32KPH, they found that the difference
between a fitted rain jacket and a looser fitting rain jacket is an 8% difference in
terms of wind resistance, which according to my estimations is around 2% slower cycling
speeds. And if you want to lift your handlebars 20mm higher, that'll cost you 1.5% from
your baseline speed. Bicycle Quarterly also found a handlebar bag was more aerodynamic than a
saddlebag, and that while a front fender reduced drag, the rear fender increased it - resulting
in no overall drag penalty. Speaking of fenders, an interesting paper came out last year suggesting
that if you fit fenders to your bike, you can make it more aerodynamic. The idea is that the upper
part of the fender shields the forward spinning portion of the wheel, which reduces the turbulence
of the air behind the wheel, and therefore, the drag of the bike. The study suggests that
fenders with specifically 135 degrees of coverage are the sweet spot between a reduction in the drag
coefficient without too big an increase in the frontal area. But any longer, and the larger frontal
area tips this balance. Based on my calculations, the 4.5% reduced Cd would mean that the fenders
could be 0.9 to 1.6% faster between 22 and 36 kilometres per hour. But this study was
conducted using Computational Fluid Dynamics or CFD. In the bike world at least, CFD is considered
more problematic than other forms of aerodynamic testing because it's really hard to account
for things like moving spokes, rotating legs, and turbulent airflow. Some companies have actually
brought out wheel shielding fenders to the market, but unfortunately, there is no independent
data that I could find to verify whether they worked as claimed. Null Winds boasts claims
as big as 20% when you're cycling into a headwind with their fenders, which to me
sounds a bit too good to be true. Birzman also teased an aero fender set which was said
to improve a wheel Cd by almost 4% at 48 kilometers per hour, but this concept never
made it to market. Another interesting example of front wheel shielding is found on the Ceepo
Shadow R time trail bike. Again, there is no data available which suggests to me that while some
aspects of the aerodynamics might be improved, there are likely negative downstream effects. And lastly, we have a study by SQLab who wanted to find out whether there was a performance advantage using their Innerbarends. While riding at 36KPH on a velodrome, they found a 14
watt difference between the Innerbarends and the grips on a flat handlebar. This works out to be a
1.8% difference in speed at the same power output. Okay, so if wind tunnels, CFD and outdoor testing
are all somewhat problematic, what can we take home from this? We really just have to go
back to the theory. Reducing the frontal area of your luggage will help you travel faster, with
the same power output. The more luggage you can jam in line with your bike the better. We're talking
frame packs, seat packs, top tube bags, and even the area under your down tube. Tighter fitting clothes
are always going to be beneficial as the shape itself is more aerodynamic, and the frontal area
is smaller too. If your body is conditioned for it, you can reduce your frontal area by changing your
body position on the bike. Using my KOGA Denham Bars, I can put my hands near my stem, or in my
bullhorns, to change my CdA, allowing me to go noticeably faster. Or alternatively, we could
all just ride aerodynamically-superior recumbent bikes. If you've enjoyed today's bike nerd content
from Oaxaca Mexico, consider subscribing, liking this video, supporting my work on Patreon,
or grabbing a book. I'll catch you next time! This is the first time ever, that I've
had to walk my bike because of the wind!
