In the world of bicycle racing, triathlon bikes are a different breed. Below we highlight a few things you need to know about triathlon bikes if you’re a beginner or in the market for your first bike.
What Defines a Triathlon Bike?
Virtually synonymous with time trial bikes, or TT bikes, the geometry of triathlon bikes has distinct characteristics in frame design and rider positioning. Most notable is a steeper seat tube angle that puts athletes in a more aggressive and aerodynamic position.
It’s also common for the saddle height on triathlon bikes to be positioned slightly higher, which promotes a horizontal, low-drag position while also widening the athlete’s hip angle. While a triathlon bike can be hugely beneficial for aerodynamics, it can also promote biomechanical efficiencies that optimize running off the bike.
The technology behind triathlon bikes is constantly evolving. Today’s best triathlon bike brands continue to push the limits with research and development, making bikes lighter, faster, more aero, and more comfortable for triathletes.
As a result, world records seem to be broken every couple of years. On the fastest Ironman courses, the best bike splits can exceed an average speed of 27 mph / 44 kph. It’s also more common to witness sub-8-hour Ironman finishes – which are largely based on a fast and economical bike split.
One of the many beauties of triathlon is that beginner and amateur athletes have the same access to high-end bicycle technology as professional triathletes.
Road Bike vs Triathlon Bike: What’s the Difference?
There are several pros and cons to using a triathlon bike vs road bike. The choice between a triathlon or time trial bike over a road bike depends on an athlete’s riding preferences (i.e. group rides vs individual time trialing), biomechanical needs (saddle and arm positioning, hip angle, comfort), and overall race goals (time trials and triathlon-specific events or a wide range of road riding).
Most beginner cyclists and triathletes are often best suited for a road bike for triathlon. Unlike triathlon bikes that are designed for straight-line speed, road bikes provide greater handling, balance, and fitting capabilities. And with minor position adjustments and the integration of aero bars, you can turn just about any road bike into an aerodynamic time trial machine.
Compared to road bikes, the geometry of standard triathlon bikes is the most significant difference, which is apparent in frame design and aerodynamic positioning (see the graphic below). Tri bikes are characterized by having a steeper seat tube angle (STA), which puts riders in a more aggressive and aerodynamic position.
For instance, the STA on most triathlon bikes exceeds 78 degrees, while on road bikes the STA is closer 72 degrees. In addition to a more aggressive STA, it’s also common for tri bikes to have a higher-positioned saddle. This position enables athletes to achieve a more horizontal and aerodynamic position while also widening the athlete’s hip angle, which can have biomechanical efficiencies when getting off the bike to run.
What’s the Difference Between a Triathlon Bike and TT Bike?
The difference between triathlon bikes and time trial bikes is largely based on subtle differences in seat tube angle, fit, and whether the bike must adhere to the International Cycling Union (UCI) regulations.
Keep in mind, triathlon bikes and TT bikes are so similar that they’re often treated as the same. In fact, some manufacturers offer a triathlon model and a TT model of the bike, just a different build.
UCI regulations defining time trial bikes are often considered the primary difference between triathlon bikes and TT bikes. A TT bike, which is made specifically for time trials versus multisport races, must have the tip of the saddle nose within 5cm/1.97inches from the center of the bottom bracket.
Because triathlon bikes naturally have a steeper seat tube angle, thereby minimizing the saddle nose-to-bottom bracket distance, this rule is rarely a disadvantage or limitation. Both function just fine on most bike trainers.
What’s Special About Triathlon Bikes?
Based on the differences mentioned above, seat tube angle and fit are what makes triathlon bike designs special. Like TT bikes, the geometry of triathlon bikes allows a larger seat tube angle. As seat tube angle increases, this puts the cyclist in a position of less drag, greater aerodynamics, and wider hip angle
An in-depth study, that looked at several performance markers points to many reasons why TT and triathlon bikes have many benefits. The first and perhaps most obvious finding was that increasing seat tube angle positions the cyclist in a more forward inclination, thereby reducing drag and improving aerodynamics.
A more kinematic analysis of the study identified greater hip extension and ankle plantarflexion at a steeper seat tube angle. As the hip angle increases the length of bi-articulated muscles crossing the hip (Biceps Femoris, Rectus Femoris, Semitendinosus, and Semimembranosus), the level of output can be optimized for power and endurance.
Additional research on hip orientation suggests that increasing hip angle improves power from these muscles – widely known as the primary quads and hamstrings.
At a wider seat tube and hip angle, kinematic relationships in the force-velocity and length-tension of these powerful muscle groups are enhanced.
Ultimately, TT bikes can yield biomechanical gains in power, strength, and efficiency, especially for triathlon. Further research has demonstrated that a steeper seat tube angle reduces fatigue associated with transitioning from cycling to running.
In summary, triathlon bikes not only improve aerodynamics, but they help optimize key muscle groups like the Biceps Femoris (or hamstrings) to enable more efficient running of the bike.
Why Do Triathlon Bikes Look Different?
As mentioned above, triathlon bikes have a steeper seat tube compared to road bikes. This widened angle opens the hips to sit forward which puts less tension on the cyclist’s quadriceps and hamstrings. This angle on triathlon bikes often exceeds 78 degrees, while on road bikes it’s more like 72 degrees.
In addition to a steeper seat tube angle, triathlon bikes often look different due to their unique frame designs. Triathlon bikes and time trial bikes typically have very narrow, thin, and tapered frames and forks.
This popular frame design delivers aerodynamic advantages that are magnified at higher speeds. Among these considerations is the yaw angle, which is the angle between a rider’s direction of motion and the relative wind direction vector. The relative wind vector takes into account both the rider’s speed and the ambient wind direction, so higher-speed TT/triathlon bikes can benefit from a very narrow, tapered frame design.
