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Forget about fancy tube shapes and integrated aerobars. The biggest difference between a road bike and a triathlon bike is the rider’s position. Because road bikes are ridden in a group of cyclists they are designed for stability and comfort. Triathlon bikes, however, have to go fast without the shelter of other cyclists so they are designed for aerodynamics.
Written by: Aaron Hersh
Road racers instinctively scoot forward onto the nose of the saddle when they need to crouch for a sprint or big solo effort because this small positional change allows them to comfortably duck from the wind. A couple cycling industry pioneers realized back in the 80’s that this aerodynamic and powerful position occasionally used by road racers is also useful for triathletes.
Why not use a road frame?
Power and aerodynamic drag determine a cyclist’s speed when riding alone on a flat road. Deep-dish wheels and teardrop shaped frames reduce wind drag slightly, but the rider – not the bike – creates the majority of aerodynamic drag. If a cyclist tries to crouch low on a road bike the angle between their legs and torso gets more acute, which makes it difficult to produce power. A triathlon frame allows the rider to sit comfortably in a more aerodynamic position by lowering their shoulders and orienting their torso so it is nearly horizontal.
Triathlon bikes have a steeper effective seat tube angle than road bikes. This moves the rider further forward relative to the cranks and allows the rider to get low in the front without discomfort in the hips. Tweak the geometry in a few more places to accommodate a lower position and improve stability, slap an aerobar under the rider’s elbow and you have a tri bike.
It took many years for this design to be universally accepted, but nearly all triathlon frames are now built with these changes. Triathlon bike fit is a complicated issue and this brief synopsis is only the most basic description of what makes tri bikes different from road bikes.
Since then, triathlon frames have benefited from improved tube shapes, integrated cable routing and many other technological advances, but a well-fitting triathlon frame is still the biggest equipment upgrade a new triathlete can make.