Time trialling (TT) is seen by some as the purest form of cycle racing. Just you and your bike competing against the clock. Unlike other disciplines of bike racing, there is no interaction with other competitors on the course, unless you catch the person in front, and so traditional race tactics are not used. There’s no riders to hide behind, no team mates to help you out (unless it’s a team time trial), and no psychological trickery from your opponents during the race. Despite the simplicity, TTs can be one of the most gruelling disciplines of cycling and is partly why time triallers refer to themselves as “specialists”. However for some the specialism of TT may be rather alien. Of course most cyclists understand the basics of aerodynamics, but those that ride time trials take these theories to the next level.
With 90% of a time trialist’s energy going towards overcoming wind resistance, aerodynamics are very important. When you hear the word aerodynamics you may think of an aeroplane soaring through the clouds, however, aeroplane aerodynamics concentrate more on powering through the air due to the large engines, cycling aerodynamics looks on the other hand to slip through the air, enabling riders to use power more efficiently, bending the air as minimally as possible.
The trick is to make the air flow more smoothly around the rider and his equipment without compromising rider comfort too significantly.
One of the most important aspects of time trialling for a rider is to reduce the frontal area exposed to air flow. This is done through the adoption of a crouching position with the arms being brought close together. To achieve this position, riders will often use bar extensions. UCI guidelines stipulate that bar extensions have to be flat, although you will find some tri athletes prefer a style of bar that is raised up. A flat back is also ideally required as this also reduces the wind flow. This can often be painful so riders will often have a slightly curved back as a compromise.
Riders also want to make sure they can open up their hip area to exert as much power as possible. Being too low can affect the rider’s pedal stroke and limit the power output. Riders will often sit very far forward on the saddle in order to create enough space to open up their hip angle and utilise the most important leg muscles used while riding in order to generate optimal power.
Below are two examples of time trialling positions at opposite ends of the scale. On the right is Bradley Wiggins demonstrating a near perfect TT position. Flat back, head looking up and minimal frontal exposure. Compare this to Andy Schleck on the left who has come under much scrutiny over his position during TT races over the last few years. As you can see Andy if sitting far more upright, increasing the frontal area exposed, which in turn increase the amount of Watts needed to power himself forward.
Helmets are probably the most noticeable thing about a time trial rider for those new to the sport. Conventional road race helmets will be covered in vents, however this is no good for the aerodynamics of the rider and so the surface of the TT helmet is smooth and solid with few vents. A tear drop style has proved very popular in recent years with this shape creating the least drag when tested in wind tunnels around the world.
There are however some variations of this classic TT helmet shape, most notably is the helmet worn by Team Europcar. These helmets feature technology inspired by the profile of a golf ball. Curves, dimples and diverts are often used to break up air the air qualities and makes them re-attach at the back of the rider/bike. This technique can sometimes be seen on bike frames and jersey sleeves.
To reduce the effects of drag, many riders opt for aerodynamic friendly clothing such as the skinsuit. The skinsuit is a staple part of any specialist’s wardrobe. A one-piece item of clothing, the snug cut of a skinsuit fits like a second skin with no loose sections to flap in the wind. Even seams are designed to be as flat possible and reduce bunching and wrinkling that would affect the air flow. Skin suits rarely have any pockets due to the short length of time trials. Despite the apparent tight fit of a skinsuit, they need to be comfortable and are often flexible enough to move with the rider through the pedalling motion.
Other items of clothing worn when time trialling will also follow many of these principles. Shoes covers are another very important piece of clothing, smoothing the air flow over the straps and buckles of your shoes.
The wheel of a TT bike is also a very crucial aspect. Rim depth is something that is very important when it comes to wheel aerodynamics. Unlike other parts on a TT bike, the wheels on a bike rotate and the front wheel has to move laterally in order to steer which can affect aerodynamics. This means a slightly different rule to static parts on the bike. Handling can be dramatically effected by the depth of a rim, this is why you will rarely see a full disc front wheel. A rim depth of around 45-60mm will usually hit a sweet spot for aerodynamics versus handling.
Disc wheels may offer the largest aerodynamic advantage, however, a severe impairment of a disc is the issue of steering in a crosswind. This makes them suitable for use as a rear wheel, but not so practical on the front. The main manufacturers of disc wheels to look out for are Zipp, Reynolds and Fast Forward.
On the front riders often use a deep section rim or a tri spoke option. In order to reduce the drag of a wheel that features spokes, the basic rule is the fewer the spoke count the more aerodynamic the wheel, however reducing the spoke count can significantly reduce the strength of the wheel, and a wheel that is unable to support the weight of a rider isn’t particularly useful.
The spinning action of a wheel can also effect aerodynamics. As the front wheel spins it pulls up air to the rear of the wheel. This can be affected by the tread of the tyre. This air is usually dispensed just below the fork crown at two o’ clock if you think of a wheel as a clock face. If the front wheel is too close to the tyre, air doesn’t have time to dispense cleanly which can increase the amounts of watts needed to push the wheel through the air.
Rear mounted front breaks have seen a huge surge in popularity recently, however, some experts believe placing the break in this position can actually work as a disadvantage as this is where all the air from the front wheel ends up and can affect the air flow.
Frame shape is often to used to free up air movement between the riders legs and over the riders arms so that when the air reaches the back of the rider there are no added Watts or extra drag.
Some frames may appear to have larger and longer tube diameters than normal road bikes, this is again to reduce aerodynamics. Tubes will often taper out to allow air a longer time to attach and flow off more smoothly towards the back. A continual gain of width allows the air to be directed to areas where it will not increase the Watts needed to push the bike through the air.
Oval shaped tubing is often used to influence air flow. Designers of time trial frames stray away from short sharp angles, rather seeking a gradual angle that air can flow over and eject out the back efficiently.
Carbon lends itself perfectly for shaping and building the perfect shapes to create an aero effective frame. Road shock abortion expends energy and Carbon can soak this up very effectively as well.
I mentioned about rider position before, but aero bars are a crucial part of the bike that help position the rider into a comfortable aerodynamic position. Some riders may think that the lower you rider the quicker your go. In terms of drag this may be the case up to a certain point, however, too much drop prevents you from comfortably looking forward and there is no point powering round a TT course if you can’t see where you’re going.
The compromise that riders need to search for is between aero position and comfort. Riders can make themselves scientifically as aerodynamic as possible, but discomfort can prevent you from exerting enough power to make this aero position an advantage. A sustainable position needs to be found in order to make the most of the power and aerodynamics that you’re producing.
So there you have it. A quick look at the science behind time trialling. Hopefully this gives you a little insight into the world of the specialist and gives you a little coffee shop knowledge to impress on your next ride. Still unconvinced all this focus on aerodynamics is necessary? Take a look at the table below which outlines the time saved over a 40km ride.