Time trialing (TT) is a purist form of cycle racing which pits riders against the clock on relatively short, flat courses. Because the essence of success is sustained straight-line speed, TT bikes (and, with some key differences discussed below, triathlon bikes) are primarily made to go fast, with other considerations such as comfort, weight and handling being secondary.
When it comes to going fast, the biggest limiter is wind resistance. Once you go over a certain speed (around 15kph), drag becomes a significant factor and the faster you go, the more drag you have to overcome. TT and tri bikes, therefore, are made with drag reduction in mind, with bike design (including aerodynamic tube profiles and integration of other components) playing a huge role in sustaining speed.
The geometry of a TT/tri bike is designed to help the rider achieve an aerodynamic position to minimize drag.
However, on any bike, the biggest element exposed to the wind and to the effect of drag is you, the rider. Because of this, TT and tri bikes are also designed with a geometry that is very different to ‘normal’ race bikes and which allows the rider to achieve a low, ‘tucked’ position on the bike, exposing the less frontal area to the wind for maximum aero efficiency.
Other geometry differences position the rider further forward so they can engage their leg, back and core muscles more effectively for a sustained effort at speed.
Wheelsets also play a huge role in reducing drag, with deep-rimmed aero wheels or even track-style fully covered disc wheels de rigueur for against-the-clock competition. These can be vulnerable to handling issues in crosswinds, however, so disc wheels are only used on the rear where they will have a minimal effect on steering.
TT/tri bikes such as the Ridley Dean Fast used by Aqua Blue Sport are characterized by features such as aerodynamically-profiled tubes, tri bars and even covered disc wheels.
At the very highest levels of the sport, scientists and designers use extensive wind tunnel testing to optimize bike aerodynamics but even entry-level machines can offer aero gains for newcomers to TT or tri. Read on for an introductory guide to the main characteristics of TT and tri bikes, the differences between the two, and what you need to look for when you are shopping for your bike.
Characteristics and features
Bar extensions enable the rider to minimize their frontal area and reduce drag. Picture: Aqua Blue Sport.
As above, the raison d’être of a TT/tri bike is going fast in a straight line, so in this category, we find a number of features that distinguish them from ‘normal’ racing bikes.
– Aerodynamics: TT/tri bikes are designed to optimize airflow and reduce drag so frames often feature ‘teardrop’ tube profiles that exert an ‘aerofoil’ effect (like the wing of a plane), cutting through the wind with minimum resistance.
Large, teardrop-profiled downtubes are characteristic of this bike type, as are aero-profiled forks and seat posts (or integrated seat masts). Some manufacturers also add drag-reducing touches such as vented forks to improve airflow around the wheels or even dimpled paint jobs which (like the dimples on a golf ball) are claimed to reduce drag and improve stability at speed.
– Geometry: As above, the biggest consideration in drag reduction is the rider, so TT/tri bikes are made to allow you achieve the classic, tucked ‘aero’ position – back flat and low on the bike, elbows and hands together, head down. TT/tri bikes will feature a shorter wheelbase, shorter top tube, lower stack height (stack is the distance from the center of the BB to the top of the head tube) and, instead of ‘standard’ drop bars, special forward-facing tri bars with the gear shifters on the extensions.
The seat tube angle will also be steeper than a standard road bike, positioning you over the bottom bracket and further forward on the bike. This position reduces drag but also opens up the hips and optimizes the engagement of powerful muscle chains in your legs, back and core. However the ‘aero’ TT position, while being efficient in a straight line, does impact bike handling and long-term comfort so a TT bike isn’t suitable for normal racing, or riding in a group.
– Integration: The pursuit of aero gains has seen many manufacturers offer bikes with high levels of component integration. Brakes, for example, are recessed or integrated into forks (or located behind the bottom bracket) and cockpits feature custom integrated stem/bar combinations.
While the extra watts may be valued by elite athletes, component integration does, however, limit the availability of aftermarket parts and may add an unwanted level of complexity to maintenance jobs.
– Stiffness: With TT/tri frames characterized by oversized tubes and massive bottom bracket shell, bikes deliver excellent power transfer ensuring every pedal stroke is translated into forwarding momentum. But all this stiffness does, come at a cost – TT/tri bikes are not generally described as ‘comfortable’.
Some manufacturers tune their carbon layups or use thinner seat stays to take the edge off, but even so, these bikes are generally not designed or intended for longer rides on uneven surfaces. Super-stiff frames and oversized tubing also add mass, so TT/tri bikes generally weigh in up to 2kg heavier than their ‘normal’ race cousins. Once up to speed this extra heft doesn’t matter (aerodynamics plays a much bigger role) but again, this makes these bikes not ideal for general riding or climbing.
TT vs. tri – what’s the difference?
The Cervélo P5x triathlon bike, with its exotic frame design, integrated front end, disc brakes and built-in storage, is a good example of a premium tri-specific bike unencumbered by the necessity to adhere to UCI rules for TT bikes.
The terms ‘TT bike’ and ‘tri bike’ can often come across as interchangeable, used to refer to bikes that place aerodynamics first and foremost. However, there are a few key differences, especially when it comes to racing: both TT and tri bikes are mostly intended for competitive use, but time trials and triathlons are generally governed by different bodies, with different rules.
The Union Cycliste Internationale (UCI), for example, sets out a very specific set of guidelines for any bike that is to be used in a time trial – they must use a ‘double diamond’ frame design, not employ additional aero fairings and adhere to guidelines for positioning of bar extensions and saddle.
The rules of the International Triathlon Union (ITU) are a little more relaxed, so bikes used for long-distance triathlons in particular (Ironman and Half Ironman distances) employ more unusual frame designs to enable riders to achieve a more aggressive position and use features such as aero fairings and integrated hydration/storage.
For long-course racing of this type, nutrition strategy is crucial, so athletes pay a great deal of attention to how much gels/bars/powders they can carry on the bike, and how easy they are to access.
What to look out for
The type of TT/tri bike you need will depend hugely on how much you want to race. As these are specialist machines you should make a realistic assessment of how much you will use it before parting with your hard-earned cash.
If you just want to ride a small local triathlon or evening TT league, for example, you may be able to achieve significant aero gains through upgrading your ‘normal’ race bike with the addition of clip-on tri bars, deep-section aero wheels or even a power meter to help with structured training.
However, this will always be a compromise as the geometry of a ‘normal’ road bike will also leave you positioned further behind the bottom bracket that is ideal for aero racing. If you do decide to go for a dedicated TT/tri bike there are plenty of entry-level and mid-range options.
As above, if you intend competing in both UCI- and ITU sanctioned events make sure you buy a bike that complies with the rules. Finally, for the serious time triallist or long-distance triathlete, a dedicated race weapon is your best option.
For your first foray into TT or tri competition, you might consider upgrading your ‘normal’ race bike with some aero features or investing in a set of aero wheels. A dedicated entry-level TT/tri bike is another option and will typically feature a basic alloy frame, likely lacking the wind tunnel-tested bells and whistles of its more expensive cousins, but with the correct geometry to enable you to achieve the tucked position.
At this level, components are likely to be basic but perfectly usable (11-speed Shimano 105 or SRAM Rival, with a speed-focused gear selection) while corners will often be cut with wheels. Basic, box-rimmed wheels found on entry-level TT/tri bikes will be fine for training, but consider an upgrade to some deep-section racing hoops down the line.
As your budget increases you’ll find a bigger range of TT/tri bikes with carbon frames – often utilizing complex frame profiles to deliver the perfect balance of aerodynamics and stiffness and higher-quality components.
At the upper end of the range, electronic groupsets will make an appearance – these have the advantage of simplifying cable routing, while button-type satellite shifters (also called ‘blip shifters’) are really useful for providing a range of cockpit positioning options. Non-standard integrated components (such as aero stem/bar combinations) will also begin to make an appearance.
At the higher end of the market, you will find electronic shifting, tunnel-tested frame design, increased integration and premium quality deep-section wheels.
Premium TT/tri bikes will use the most exotic materials and latest design innovations to deliver the ultimate in clock-cheating race weaponry. Look for top-end electronic groupsets such as Shimano Dura-Ace Di2 or the almost-wireless SRAM Red eTap, as well as high-quality, deep-section carbon wheelsets which are ready to race.
Long-distance triathlon specialists will also want to consider tri-specific bikes which may employ radical frame designs to achieve an aggressive position and which also come with integrated hydration and storage compartments and even aero fairings.
When it comes to choosing the right TT/tri bike, the most important thing to consider is the fit. Bikes of this type are intended to be ridden in the ‘aero tuck’ position so you will need to find a frame size/geometry that enables you to both achieve this position and sustain it, comfortably, for as long as you need to race.
Pro bikes will be characterized by a short head tube and extremely low stack height that enables racers to adopt a flat-backed and aggressive position, but their ability to do this has been developed over years of training and racing.
If you haven’t got the flexibility of a pro you will need to find a bike with a slightly more upright geometry so you can ride comfortably. Some higher-end TT/tri bikes enable the frame geometry to be tuned so you can dial in the perfect fit, with spacers or extensions that lower/raise the head tube height or cockpit dimensions.