Time Trial Races
26 Oct 2005
- Aerodynamics -
Air resistance represents about 90% of the effort that the cyclist develops when pedaling on a flat course at speeds of 30-35 km/h and higher.
The research for the most aerodynamically advantageous position for time trial races is then of the utmost importance.
Trying to reduce the frontal area of the athlete’s body while pedaling usually brings up some extreme positioning, allowing a decrease in aerodynamic resistance up to 35% less than the usual road bicycle position.
Very often though the most aerodynamic position implies also a decrease in pedaling efficiency and an increase in the metabolic cost of the gesture, with a consequent reduction of the average power output of the cyclist under effort.
This power drop can be very relevant (even between 10-20%), and for such reason it ought to be quantified by tests simulating race intensities, either on the road or in the lab.
With specific uphill training while keeping the aero position it is possible to reduce such power loss.
It is opportune then to compromise over “aerodynamic” and biomechanic” efficiency, especially when it comes to stage races, because the cyclist may show signs of muscular exhaustion/uneasiness in the days after the event.
Wind-gallery tests are very useful, but also very expensive and not so easily accessible.
Personally I’ve always used an extremely simple test, absolutely costless, in order to check the aerodynamic advantage of different positions on the bike.
All we need is a 200-300m long descent, steep enough to allow speeds of about 50 km/h without pushing on the pedals, immediately followed by an uphill distance so to slow down and stop the movement of the cyclist in a reasonably short time: the farther the cyclist stops, the more aerodynamically efficient is the position.
Obviously it takes several measurements and try-outs in order to limit the influence of external factors, such as variations in wind speed or temperature, but in the end the results are reliable.
To make it even more realistic, the cyclists should “empty-pedal” (i.e. with a 39x25) during the descent, so to reproduce the kind of turbulences of moving legs.
It is also possible to test special materials, such a wheels, handlebars, tires, helmets etc…
- Rolling resistance -
Often underestimated, rolling resistance is mainly due to compression-deformation of the tires and to ground surface.
It is in inverse proportion with wheels diameter and tires pressure.
The type of tires (clincher or tubulars) and their diameter are also relevant, together with friction due to mechanical parts (hubs, bottom bracket, chain, etc).
Rolling resistance becomes more important in uphill distances, because of low speeds and lateral wheels and tires “stress” typical of off-the-saddle pedaling: such deformations, although minimal, waste a rather remarkable amount of the power developed by the cyclist.
- Cranks and pedaling cadence -
Cranks that are longer than the usual road bike are often used on time trial events: this is generally advantageous in terms of performance for the race itself, but the change in the pedaling style may bring about muscular uneasiness for the successive 2-3 days during a stage race.
My suggestion is to lengthen the cranks not more than 2.5mm, and to timely adapt to the change with specific time trial bike training.
The ideal pedaling cadence varies in accordance with the power developed (see High RPM articles on 53x12.com) and with the kind of muscle fibers of the athlete: a predominance in slow-twitch fibers (type I) will suggest higher cadences (95-105 RPM), while a predominance in fast-twitch fibers (type II) will suggest lower cadences (80-90 RPM).
- Distribution of the Effort -
A prudent start is optimal: keeping a power output that is 5% lower than the usual average wattage developed in such races, for the first 4-5 minutes of effort, allows the cardio-respiratory system to reach the maximum efficiency without and excessive lactic acid accumulation that could be “fatal” for the remaining of the event.
If the cyclist for that kind of time trial usually develops an average power of 300 watts, he should then keep a wattage of approximately 285 for the beginning 4-5 minutes.
Should the course present short climbs or headwind distances, it is advantageous to face such conditions by pushing slightly higher power outputs (between 5-10%) than the average wattage, while reducing them in the most favorable distances, instead of trying to keep a constant power throughout.