Really, I can't think of anything more relaxing than driving on little traveled roads paved over rolling hills as they cut through pristine ranch land along the foot of the Rocky Mountains–with a cup of good coffee and some killer tunes. To add to this glorious alone time, the scrub oak along the this road still held some of their fall colors. I felt like I was driving in New England, not south of Denver towards Colorado Springs to visit Carmichael Training Systems' home office and training center.
I made the trip to have coach Lindsay fine tune the fit of the Trek Speed Concept 7.5 they are loaning me for Ironman Cozumel. She used the Retul bike fit system and was able to compare my fitting on my Trek Madone from last April. I will write more on this later, but she was able to dial it in so the crucial comfort and power angles pretty much matched my road bike. The big difference, and what sets a triathlon bike apart from a road bike is how those body angles work with the geometry of the bike.
On a road bike your weight is more evenly distributed over the entire wheelbase which allows it to climb up hills and corner more smoothly. A TT bike's geometry puts you forward and over the top more and rotates your hips so that your back is more parallel to the ground even though your hip angle, the angle of your thigh to your spine, remains the same. This is why it appears people on TT bikes are "laying over" their handle bars and what makes them more aerodynamic. It's critical to keep the hip angle wide enough to generate power and not be crunched over the top tube.
I am not a flexible person–at all. For example on my road bike, my back is 31 degrees angled up from the road which is not terribly aerodynamic. On my TT bike now, with same hip angle, my back angle is now 19 degrees. In other words my back is more parallel to the ground. That is a huge aerodynamic advantage. With my hip angle being the same, in theory, I should be able to generate the same power as on my road bike, but with the increased aerodynamics I should be able to go faster.
The argument has been made that a TT bike saves your hamstrings for the run because it isolates your quads more due the forward position. Coach Lindsay has her doubts how much effect that has on setting up the athlete for a stronger run. What more likely happens is that the athlete uses slightly less energy to go a bit faster than usual and thus has fresher legs for the run.
So why not just ride a TT bike all the time? Well, if I lived in Nebraska and only cycled on farm roads, or if all I cared about was Ironman's I might. But here in the western suburbs of Denver most of my rides involve climbing and varied terrain and my road bike is simply more comfortable and efficient in this mixed environment. Also, a TT bike is very rigid. The rigidity transfers the maximum amount of power to the drive train to move it forward. But, it jars you and can take it's toll over a long distance. A road bike is a bit more flexible and cushions the ride making it more enjoyable to ride on longer distances.
Tomorrow I will take it for a three hour ride and should really feel the difference the fit made!