Triathlon Bike vs. Road Bike
July 9, 2007Everybody keeps asking, “should I get a Triathlon Bike or a Road Bike?” Well, here I’ll explain (and show) the differences, and attempt to convey the benefits and drawbacks of one versus the other. In following posts I’ll help you walk through the actual bike buying experience.
There are three major differences between a triathlon bike and a road bike. One difference, the frame geometry, is what actually determines the literal definition of a Triathlon Bike versus a Road Bike. The other two, aero bars and wheel size, are also a part of the whole equation.
The true deliniator between a “Triathlon Bike” and a “Road Bike” is in the frame geometry. The frame is the core of a bicycle and the main part to which all of the other components are fitted. The frame geometry refers to the angles and shapes of the frame’s tubing. An image from a similar article on the Bike Sport Michigan website is helpful in showing this difference:
This standard frame design is referred to as a diamond frame. As you can see, each of these frames is comprised of two triangles sharing a common tube–the seat tube. The angle of the seat tube differentiates a Triathlon Bike from a Road Bike. The image above clearly shows the difference between a standard Road Bike, which typically has a 72°-73° seat tube angle, and a Triathlon Bike, which will have a seat tube angle of 76°-78°.
What effect does the seat tube angle have on a rider? Well, the steeper the seat tube angle, the more effort is exerted by the cyclists hamstrings compared to his or her quadriceps. That means a Road Bike allows you to use your bigger muscles (quadriceps) more and therefore you can exert more power relative to a Triathlon Bike. It also means, when you get off the bike, your quadriceps are more tired. No big deal if you are done for the day. Big deal if you still have to do some running.
To make up for the reduction in power that a steeper seat tube creates, a Triathlon Bike will typically have one or both of the following compensating features: aerobars and smaller wheels.
Aerobars serve two major purposes. First, they put the cyclist in a more aerodynamic position. This drastically reduces wind resistance at higher speeds. Second, they allow the cyclist to ride in a more restful position. Aerobars are almost a necessity for any triathlete. It’s important to note, however, that aerobars can be installed on nearly any type of bike by using clip-ons.
The main difference between built-on and clip-on aerobars is the positioning of the shifters. You will have bar-end shifters on built-on aerobars, as shown in the picture below. Notice the shift levers at the end of the aerobars and the brake levers at the end of the handlebars. This is designed for racing efficiency; you do not have to come out of the aero position to shift. This also means that you cannot brake and shift from the same position. Riding with this style of aerobar is not for beginners. Built-on aerobars now come standard on most mid- to high-end triathlon bikes. 
The following picture depicts clip-on aerobars. As you can see, these mount directly to your existing handlebars and allow you to ride in the same aero position as with built-on aerobars. The main difference you’ll find with clip-ons is that they do not have bar-end shifters. You shift and brake from the standard position on your handlebars.
Learning to ride in the aero position is a bit tricky. You give up quite a bit of control with regard to both maneuverability and functionality (shifting and braking), but the results typically worth the effort.
If you decide to put clip-ons on a standard geometry road bike, you’ll probably need to adjust your seat forward and reduce your stem length. Otherwise, you will be much too stretched out, resulting in reduced power and increased fatigue, and negating any of the benefits of the aero position.
As for wheel size, there was a time when many triathlon bikes came with 650c wheels. These wheels are smaller than standard 700c wheels and supposedly offer faster acceleration, greater climbing ability, and a reduced profile (smaller wheels = less wind resistance). Technically, these benefits are all true. However, as a matter of practicality, there are very few instances in which the benefits of 650c wheels outweigh the drawbacks.
First, if you’re learning something from this post, you’re probably not fine-tuning for the 12th leg of the Tour de France. In other words, you don’t have a different bike, helmet, shoes, sun glasses, etc. for each ride you take. If this is the case, and you have the choice, I suggest sticking to 700c wheels.
So there you have it. You now understand the fundamental differences between triathlon and road bikes. To further your bike knowledge, I’ll leave you with the following bike-frame schematic from Wikipedia:
