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!