Easy Speed - Cobb Cycling

Easy Speed
So, you’ve decided to take the plunge and join a couple of your buddies and do a triathlon. This will be
fun, a whole lot of work but the rewards will be great. As with most new hobbies and particularly one that
will affect you both physically and emotionally, learning more about the sport should make it more fun. This
is not quite the same as joining in on a bike club group ride, not much like showing up to meet a couple of
buddies for a Sunday morning run, triathlons are an individual sport where you race against the clock. As the
years roll by, you generally won’t remember who was in your age group at a certain race but you will
remember your race time for the different courses. I started my triathlon racing in the early 1980’s and still
race today. It’s a fun, long term hobby.
As your riding improves and you begin to develop a higher level of fitness, it’s almost normal to look at
the other riders and think to yourself, “I can take him this season” and set that as a goal. The cycling part of
triathlon is certainly the area where you can lose the race. It’s easy to use up so much energy that you can’t
run or at least not as well as you had hoped to. More training miles will always help but smarter equipment
choices can play a big role in the outcome. In November 2009, I was conducting some wind tunnel test for
several Elite racers. I decided to spend a few test runs gathering some base line data for the new racers
coming into the sport.
As you read through the issues of Triathlete magazine or other magazines about the sport, you see
references to “wind tunnel tested” or “wind tunnel developed” for many different products. To add to this,
there are many advertisements that quote “Worlds Fastest” for their products. Often two or three different
brands make this claim for their products and this can easily be confusing for the new racers in our sport. So,
how do you separate out the hype from what things can really help you compete and have more fun? During
testing at a wind tunnel, the rider and the bike are basically inside a large tube that has air pulled through it.
As the air blows over the rider, the sensors that are mounted under the floor of the wind tunnel that the bike
mounts to, “flex” from the air pressure going over the rider. The “flex” that the sensors feel is converted to
“Drag” or pressure on the object. To help make a rider go faster, modifications to rider position and
equipment simply try to reduce the drag that a rider has when air goes over him.
These are pictures showing the mounts that riders never get to see under the floor. The bike attaches to these
stands. The “balance” is a huge steel platform under the stands and this is what measures the “flex” or drag.
Another tool for testing at the wind tunnel is to the use of smoke to help visualize how the air is going over
the rider.
While testing with smoke makes for great photo opportunities, smoke
doesn’t give you any hard numbers, only ideas and directions to pursue
when looking for more speed. I thought that a quick tour of a wind
tunnel might help you better understand the mechanics of the testing.
Why go to a wind tunnel and do all of this testing anyway you might
ask. The answer is that to make educated guesses and to find a
consistent path of improvement, you must be in a controlled
environment. Testing outdoors has too many variables such as
changing wind directions, temperature and air density to be a quickly
repeatable test situation. Wind tunnel time is expensive, $500.00 $1000.00 per hour but it’s the only way to truly quantify the end results.
Many times you will go to your local bike shop and ask how to improve your cycling. The answer is
usually to get a new bike and new wheels followed by the one always good advice to “ride more.” But let’s
say that you just got your bike and and spent your equipment budget for the year but would still like to go a
little faster. What is the separation of truth from marketing hype? What will really give you the best “bang
for the buck?” I test and develop products for many different companies. Most of these products are for
future years and used to set directions for the companies. I often take Pro and Elite level cyclists to the tunnel
to tune their positions and look for that last bit of speed. So it’s easy to forget about the base of our sport new riders just entering into competitions. Recently I had a local rider come and join me for a round of wind
tunnel testing He brought his road bike and standard cycling gear. I felt this would be fairly typical of what a
new racer would experience so we gathered some test information including power [watts] numbers to use as
a base line. My goal with this article is to clearly show how much difference just a few simple changes can
potentially make for you. Then you can decide the value of time vs. dollars.
These three pictures relate to the graphs below. In the first picture the rider is on a standard road bike using a
standard road helmet. In the second picture, the same position but we swapped for an aero helmet. In the
third picture, we had the rider lean forward to simulate using aerobars while using the aero helmet.
On the above graph, the top line is our base line road bike rider. The numbers represent “pounds of drag.”
This is often expressed also as “drag in grams” or “CdA” for coefficient of drag times area. Confused? The
bottom line for the racer, is that the lines are always the same. The time savings or gains are always the same
and lower numbers are always better numbers. At the bottom is the term “yaw.” This represents the cross
wind effect that all cyclists experience on the road. Studying how things are affected by crosswinds is very
important. We deal with them on every ride and it is quite often the case that two similar test objects will
react very differently at various crosswind angles. You can recognize this as bike stability or your bike
feeling “twitchy”. Now, I’m going to add some real world numbers as to the effect of the changes we made.
I’m going to use two examples of rider power and show the effect over two distances: the classic 40kilometer, Olympic triathlon distance, and the 180k “Ironman” distance. Rider power obviously affects the
time potential for a rider. We can easily measure rider power now where just a very few years ago very few
riders knew their numbers. Training with power is a very useful tool but it will not overcome bad
aerodynamics. It takes a large increase in power to offset bad aerodynamics.
40K DISTANCE
Weight
75 kg
75 kg
75 kg
Watts
165
165
165
Drag
8.21
7.91
6.35
1 hour 17 minutes 16 seconds
1 hour 16 minutes 24 seconds
1 hour 11 minutes 33 seconds
75 kg
75 kg
75 kg
220
220
220
8.21
7.91
6.35
1 hour 9 minutes 11 seconds
1 hour 8 minutes 23 seconds
1 hour 3 minutes 56 seconds
Watts
165
165
165
IRONMAN DISTANCE
Drag
8.21
5 hours 47 minutes 40 seconds
7.91
5 hours 43 minutes 48 seconds
6.35
5 hours 21 minutes 56 seconds
Weight
75 kg
75 kg
75 kg
40 K Time
1:17:16
1:16:24
1:11:33
1:09:11
1:08:23
1:03:56
180 K Time
5:47:40
5:43:48
5:21:56
(I did not put in 180k times at 220 watts, for new riders it is very unlikely that you could sustain that power
level for a five to six hour ride.) (in italics)
As you examine the above numbers you can see that there are some large time gains to be made by using
aero bars and choosing a more aerodynamic helmet. There are small differences in aero helmets but
generally, they all are measurably better than a standard road helmet. Using aerobars is very essential to
better time-trialing performance. Installing aero bars but being able to use them because of rider discomfort
is a very common, but unfortunate situation. The latest and greatest bike doesn’t necessarily mean it’s the
best bike for you. Rider comfort, which enables you to ride for long periods of time on the aerobars, is
essential. For a small investment of $100.00 to $300.00 you can make a significant improvement in your
cycling equipment. These changes along with good bike positioning will help lead you to a better cycling
position which will also help you run faster off the bike. Important considerations for aerobars are their
adjustability and general comfort. Bars that are not adjustable fore/aft should be avoided until you have
established your correct position on your race bike.
I’m going to do some further wind-tunnel testing in February 2010 regarding clothing and number
placement. It is easy to get wrapped up in the high-end equipment world and forget the basics. I plan to
show how clothing choices are important and whether that race number flopping around on your back is
good or bad.