Let's first consider the physical differences between triathlon bikes and road bikes and how those differences effect a rider. The obvious difference in appearance between the two bikes is their cockpits, but the more important distinction is found within the geometries of the frames.
A triathlon bike has a steeper seat tube angle - that is - the seat tube is closer to vertical than a road bike's. This steeper geometry places the rider's hips over the crankset which engages their quadriceps more for increased power. Additionally, this distribution of muscle use makes the transition to the run much easier. With the rider's torso also in more forward position, their upper body weight becomes supported by their skeletal rather than muscular system, staving off fatigue. Despite a rather aggressive looking position, the rider is comfortable and aerodynamic, increasing their efficiency.
A road bike with its' more traditional bicycle geometry puts the rider in a better position for climbing, sprinting, cornering and riding in a group. With less of the rider's weight over the front wheel, the bike handles in a more predictable manner. Equipped with drop handlebars and integrated brake/shift levers, a road bike can give a rider more confidence with their hands on the brakes at all times while still offering multiple positions on the handle bars. Road bikes tend to weigh less too. A road bike offers versatility and comfort for a variety of uses, from recreational riding and commuting to many types of racing.
So, which bike is better? More importantly — which bike is most appropriate for you? Decide what type of riding you want to do and what expectations you have regarding the performance of your bike. Here are a few questions to answer:
By now, you can see where this is going... If you answered yes to the first two questions, specifically - if you want to complete a triathlon in the fastest time you are capable of - we're going to recommend a triathlon bike. Based on our experiences, most riders will be approximately 2+ mph faster on a tri bike than on a road bike. If you answered yes to the last two questions, the versatility of a road bike will most likely be your best solution.
The geometry of a triathlon bike makes it much easier to be comfortable and powerful while in a very aerodynamic position. Notice how David Thompson's pelvis is almost directly over the bottom bracket, which allows for a much more open hip angle despite his low aerodynamic position up front.
This is Claire Bootsma on her road bike. She's seated further back in relation to the bottom bracket (her hips are positioned between the bottom bracket and hub of the rear wheel) which makes for a more efficient transfer of energy while climbing, pedaling at a higher cadence and generally makes the bike easier to handle over a variety of terrain.