Tuesday, June 16, 2009

Time Trialing

When the weather cooperates, I have been participating in a bi-weekly time trial series organized by Wild Card Cycling teammate Martin. Our race is known locally as the Seymour Time Trial series, which is contested on a 10.85-mile out-and-back course that starts and finishes in Seymour, Illinois. Seymour is a small and somewhat depressed farming community about 8 miles west of Champaign, which means that it doesn't have a lot of traffic. However, it is served from the south by a mostly smooth asphalt road in much better condition than the more prevalent oil-and-chip surfaces I often encounter in training.

The Seymour Time Trial out-and-back course

The time trial, also known as the "race of truth", is the purest form of bicycle racing. Each competitor rides alone on a fixed course, without the ability to draft behind other riders.

Any sort of wind is detrimental to cycling performance, and the stronger the wind, the greater the punishment. One might at first assume that the wind would be a neutral force in a race that starts and ends at the same point. A headwind and tailwind might balance each other. However, a (simplified) examination of the math and physics involved reveals otherwise. For example, in the absence of wind, suppose a given rider might be able to hold 25 mph. The rider will encounter some drag even in calm conditions due to the apparent wind generated by his motion. From fluid dynamics fundamentals, the power required to overcome wind resistance is approximately proportional to the cube of the apparent headwind. (Note that a cyclist almost always faces an apparent headwind or net headwind, or more technically, a yaw angle within 90 degrees of a pure headwind. If the wind is blowing faster that you can ride in a tailwind, get off your bike, crawl in a ditch, and cover your head!) But a given wind that slows the same rider to 20 mph in a headwind would allow him to ride about 30 mph in a tailwind with approximately the same power output. In order to average 25 mph, the rider must spend equal amounts of time at 20 mph and 30 mph. On a course that starts and ends at the same spot, that is not possible. The rider will spend the same amount of distance at each speed, but the time spent at 30 will be much shorter due to the faster speed. Also, for a fixed power output of the rider, as windspeed increases, average rider speed drops faster than linearly.

Our first 2009 running of the Seymour Time Trial was contested in very windy conditions, perhaps 15-20 mph. At least the wind came from the south, dealing riders a headwind on the way out and a tailwind on the way back. If the wind must blow, this is the preferred direction as it allows the rider to fight the headwind in a fresher state and recover into the tailwind. Crosswinds can often be harder that the headwind/tailwind combination because the rider must expend energy just to keep the bike upright and moving straight ahead - energy that is not available for the objective, which is to move down the road as fast as possible. Still, I managed a 24.1 mph average on the first outing and was only 3 seconds slower than my best time from 2008, which I achieved on a calm day. This year, I logged a greater volume and quality of early-season training, mostly from my Wild Card Cycling spring training camp and preparation for an early May triathlon. I was looking forward to taking another shot on a calmer day.

Our next scheduled running of the time trial was stormed out. Winds were very gusty and racing would have been dangerous. Two weeks later (June 16), the forecast looked ominous again. Rains feel early in the day and the hourly forecast at the weather channel called for a possible clearing, but persistent 15-20 mph winds. As it turned out, the winds calmed considerably when the skies cleared, easing to about 7-8 miles per hour. The wind was again out of the south.

I felt pretty good, though a little tired from traveling back from Florida the night before. I was the first rider to start and was passed by the former 40+ state champ about 4 miles into the ride. When he came around, he was mashing a massive gear at maybe 70 rpm into the headwind. He must have been simulating hills or something and not even trying to do his best time, but he still averaged almost 28 mph. I held about 22-24 into the wind and 27-31 with it. The result was an improvement of 1:12 over my best effort of 2008 and an average speed of 25.25 mph. For the moment, I am third on the 2009 Seymour Time Trial leaderboard, but several strong riders were not present during the second running with the more favorable conditions.

Here is a partial ride profile from that running. (Most of the first mile was lost due to a shutdown of my bike computer, and about 200 meters of freewheeling after the finish was also recorded before I shut off the timer. Also, the heart rate readings are a little crazy and distorted into the headwind due to "flapping jersey syndrome".)

The time trial is a form of racing that suits me well. I have a lot of practice from triathlon and occasional commuting to work by bicylce. The bike leg of triathlon, at least in US events, is essentially a time trial. My athletic profile seems to be well-suited to the discipline. The more I ride, the more I learn that I am able to hold a pretty high level of average power, but I don't have much acceleration or top-end speed required to be a good sprinter or criterium racer. Put another way, I have good slow-twitch muscles, but lousy fast-twitch muscles. I'd like to think that I am not a shabby climber, either, but I don't get much practice on hills and haven't really been tested. I did fare better against the competition in the modestly hilly Hillsboro-Roubaix race than in my other mass-start cycling races.

Without the ability for riders to share the load and take turns sitting on the front, aerodynamics are critical in time trialing. I have recently acquired some gear to help me reduce drag and improve my performance in time trials and triathlon. I've been using clip-on aerobars for some time, but have recently added an aero helmet, shoe covers, a wheel cover to convert my standard rear wheel into a "poor-man's disc wheel", and a deep-section carbon tubular Zipp 404 wheelset (which made me poor after I purchased them. I'd like to eventually get a dedicated time trial bike also, but that purchase will have to wait.)

The Giant TCR C1, race ready with new Zipp 404s and aerobars.

The disc on the rear wheel reduces drag significantly, but makes the bike hard to handle in the crosswind. A disc on the front wheel is always a bad idea (except on an indoor track), since even a slight crosswind pushes the steering out of line. So far, I have not had the opportunity to use the new wheels or wheel cover in a timed event, but I should have them at my disposal for my next triathlon. I am pretty optimistic about my prospects, especially if the morning wind is calm.


Ragfield said...

Nice wheels! I'm definitely fearing your time trial prowess this year...

Scott said...

Fear the wheels, Rob! You can definitely hold your own against the rider.