Flat versus Climbing TTs
The 2013 time trial stage of the Tour of California comes to mind. Put yourself in the shoes of a member of that thrashed peleton, readying yourself for the effort, still unsure of the right choice of equipment. Once in motion however the air becomes your ally and once in full flight mode the power comes smoothly as you breeze swiftly along a flat road at speed. But then all bets are off.
Jens Voigt during the time trial in California this year.
As you begin climbing near end of the race, the grade forces you into a compromised stance that does not suit your biomechanical ability to “leverage power.” Your speed drops precipitously as you reposition your weight on this otherwise perfect TT bike. As you change your muscle recruitment patterns, you begin compromising key force vectors that otherwise provide smooth transfer of energy on the flats.
Climbing is the most challenging part of any time trial testing protocol, and therefore a prime consideration as we move forward with our testing. Some of the TOC riders when faced with such demanding options actually chose to dismount and jump on their waiting road bikes. Was this the best solution? Possibly not. But if testing of aero equipment had been done in advance on such varied similar conditions, this issue would not have been a debate and times might have been more predictable which is another way of saying “faster.”
Practical Aero Testing
In our last article, we introduced you to the principles of testing and provided a protocol that can be applied to any parameter you wish to test. Now let’s apply those principles and the protocol to the aerodynamic test case, and along the way, we will highlight practical issues to help you with the choices and preparation.
First, we need to define the goal of the test and what we have to work with. What components do you want to test? Is it the effect of a new position, new set of wheels, or new handlebars?
The relevant parameters for this test are:
The primary parameters are average power, average speed, wind speed, wind direction, course length, course profile, elapsed time, bike setup (including tire pressure and other weather conditions.
The controlled parameters are:
Average power (or average speed), course length, course profile, bike setup (tire pressure and NO CHANGES in the set up)
The parameters we can vary:
Bike position, wheels, handlebars.
The variables that can’t be controlled:
While we can’t control the weather, wind speed and wind direction need to be monitored. The effects of small variations can be minimized by averaging the results of multiple tests.
Say that you want to test a new position. First, identify a course for testing that is long enough to have a steady effort but not so long that a constant speed can’t be maintained. To test only aerodynamic performance, look for a flat course about 1 km without obstacles. Second, decide if you will ride at a constant power or a constant speed. If you select a constant power, you will be looking for the change in the average speed. If you select a constant speed, you will look for changes in average power. Whichever you select, use the power level or speed you are targeting for your event.
Next, determine the baseline. Using your original position, or original wheels, perform the test 5 to 10 times. The number of repetitions can be reduced if the results for each repetition is similar. If the results are not similar, determine if the weather conditions are varying too much or if additional repetitions can be used to average out the variations. Consider increasing the number of repetitions. If you are using an out and back course, record the outbound results separately from the inbound results. It is important to record the data for each repetition, so having an assistant to time and log the data is advisable, but not essential if you are well organized.
After the baseline test is completed, make the adjustments to the bike and repeat the tests. Again record the data for each rep.
Once the data has been collected, calculate the average values for the parameter measured. For example, if the test was done at a constant speed, calculate the average power for the baseline tests and the average power for the modified setup. Subtract the average of the baseline tests from the average of the modified setup, remember if you are using an out and back course, keep these separate. The result of the two can be averaged. In this case, A DECREASE IN THE AVERAGE POWER (a negative number) INDICATES AN IMPROVEMENT IN AERODYNAMICS.
You may be asking, can I really test aero without a wind tunnel? The answer is yes. Of course tunnels have advantages, and if you can afford the testing which is hundreds of dollars per hour, it should yield results. However, the simple field test can give you very good results and quite possibly better replicate the actual real world conditions on the road.
Some things to consider about aero testing versus what you may encounter in your time trial. In the field test, there is no control of the wind direction. If your TT course has a predictable wind direction, you can do your aero testing on a course with a similar wind direction. However, the results only apply to the wind direction tested. Wind tunnels can control the yaw angle (direction of the wind) over a limited range. In this case, if the prevailing winds fall into those angles, you could apply the data. However, if the wind direction is different from what was tested all bets are off.
Don’t get caught up in testing only aero dynamics. For example, the optimum aerodynamic position may hinder torque to the pedals on a climbing section, or compromise a low back. It is important to test for power efficiency versus your baseline. If the TT course has a steep climb, like the TOC, a similar grade should be tested. The goal is to find the best trade off between aerodynamic efficiency and power efficiency for the course you will be riding. Often times this means slight tweaks in the mechanical set up. In future installments we will address the biomechanical set up as well, covering the critical points few fitters ever delve. We will address the idiosyncrasies of bodies and the varied therapies and mobility exercises that arrest muscular impingements and address inflexibilities that cost us that all important power.
John Howard is one of the pioneers and true legends of American bike racing with palmares including: 3-time Olympian, Ironman world champion, bicycle landspeed record, USA Cycling Hall of Fame, and elite and masters national champion. John is also an active cycling coach and the author of Mastering Cycling. Check out more information about John and his coaching at www.fittesystem.com and www.johnhowardsports.com.
Doug Dunn is a level 1 FiTTE practitioner with a deep interest in how to meld the rider with the bike. He is a long time competitive cyclist and electrical engineer with an extensive background in the development of test protocols.