In Depth - Road Bikes vs. Triathlon Bikes

I am constantly asked what the big differences are between road bikes and triathlon bikes. The obvious difference is the fact that one races a triathlon in an aero position, but sometimes we see aerobars on road bikes so what is the real difference? There is a smaller difference between UCI legal time trial bikes and triathlon bikes, though they look very similar. The short answer is, road bikes are designed to have three hand positions, triathlon bikes are designed to have one. Just because a road bike has clip on aerobars, it does not imply that it is a purpose built triathlon bike.

Draft legal triathlons are the one area where a road bike is used with little stub aerobars, but positionally speaking, I call them road bikes. They are designed to be able to do all that a road racing bike does and in fact, bicycle racers use the aero position of a draft legal triathletes all the time.

Time trial bikes that are UCI legal have saddles that are set back further than triathlon bikes. The bike is setup so the rider has to actually ride on the nose of the saddle (on the rivet, as they say) to get the proper balance point for the effort being produced. The harder one pedals, the farther forward their balance point moves.  Since a time trialist is racing at max effort, the most efficient position is in front of the comfortable point on the saddle, so riders just tough it out. They don't have to be comfortable and their events are rarely longer than about an hour so who cares?

Triathlon bikes are designed to be ridden for longer distances and at a submaximal pace. This means that the rider will be putting more weight on the saddle and aerobars because they are not pounding the pedals hard enough to support themselves. As such, the saddle and aerobars are located in the place the rider is the most efficient or most aerodynamic. The reason I distinguish between the two is traditional triathlon positions are very far forward to accommodate a triathlete’s greater hip angle needs and to allow a super aero position.

My problem with this position is twofold. First, the position is not powerful and many triathletes give up more power than is gained by pure aerodynamics. Second, the further forward one is positioned relative to their balance point, the more front loading occurs on the knees and overcompensation by quadriceps occurs. This muscle imbalance is paid for in the transition and the start of the run.

The perfect triathlon position is the one where the rider is as strong and aero as possible, with enough comfort to be able to stay in the aerobars the entire event. This is a biggie. If you have to sit up during a race to rest because the aero position is not sustainable, you have a problem. You will be going slower and you will be more fatigued in the run. Remember, though, power trumps aerodynamics to a point, so your best position may not be where you think it is!

Since the position on the bike and the setup of the bike to support that position are the two defining differences between a road bike and a triathlon bike, what about all the aero tubing on some frames and the round tubes on others? Some frame manufacturers advertise how fast their frames are based on wind tunnel testing, but I think that is a lot of marketing hype for the most part. Here is a critical fact: The part of the time trial or triathlon bike that creates the most drag is the rider! The frame is inside the boundary layer and as such doesn't make as big a contribution to aerodynamics as one might think.

The concept of a boundary layer is a tough one so imagine the air right next to you going the speed you are, and at a certain point away from your body (and the bike) the air is undisturbed. There is a "layer" of air that transitions from no disturbance to actually going your speed, as the layer of air molecules that touch your skin are doing. The stuff in between is the "boundary layer."  In my industrial design career, I remember designing a part that went on a Boeing 777, and I remember learning the boundary layer was 13" thick at the point in question. This means that the 2" part that was sticking out of the fuselage had virtually no real aerodynamic detriment!

What all this means is, a road bike with aero tubing still won't be as fast as a triathlon bike with round tubing, assuming the rider has a good position! What this also means is, the aerobars, fork and front wheel have a huge impact on aerodynamics as they are outside the boundary layer. Some very fast Ironman finishes occur with people riding round tube triathlon bikes, but you can bet they are positioned correctly and have good wheels, aerobars and front fork.

At the end of the day, there is a lot to a good triathlon bike. The first thing, positioning, is the most critical. Second, great wheels are important. Third, having a good set of integrated aerobars that have the shifters at the ends of the aerobars is important. Next, hydration. Frame bottles or aerobar bottles / hydration systems are much better than those behind the saddle. You have to move around to reach back and get those saddle mounted bottles, so that is an area that could yield good results.

Triathletes are in charge of all of the aspects for all three disciplines in the sport. The bike is so critical and yet so overlooked it is not surprising that much bad information travels around the transition area. When you are sitting around the cooler after a race, and someone says that "Brand X" bike won 10 Ironman's, remember, the bike frame didn't win the race. The athlete did, who had the best time in all three legs! I hope this is good food for thought and I am happy to answer any follow on questions that result from this reading.