There are some fitters and manufacturers that would have us believe that a more forward saddle position relative to the bottom bracket, or a “steep” seat tube angle on your TT/Triathlon bike is the better and faster decision. Put more simply, their argument is “forward is faster”. Well, I’m all for simplicity, so I reckon if I had to boil down my thoughts on the TT/Tri bike positioning topic to a catchy little phrase, it’d be: “faster is faster.”
The logic of these expert fitters and purported knowers of all things fast has a great hook – that is, in the same sense that arguing about moment of inertia for bicycle wheels is a great hook. The argument/story makes sense in both cases, and there is definitely an effect. The question that remains, though, is how much does it matter? In the case of wheel moment of inertia, the answer is “not much”. How’s it shake out for dorkin’ around with saddle fore/aft position?
Supposedly, the art of going fast is all about preserving the angles - the most critical one being hip/torso angle (there is some ambiguity on how this is actually defined, but reference the image below for a stab at it). The argument goes that one must preserve this crucial hip angle in order to preserve pedaling power. When this need for maximum power is balanced with the need for aerodynamic slippery-ness in a TT/Triathlon situation, the eureka solution was proposed: rotate around the bottom bracket (BB).
When one rotates around the BB, all the angles are preserved, and theoretically, the front end (shoulders/back) are lowered. This can be true for certain folks. The question remains, though, is just how much does one realistically have to rotate/move the saddle forward in order to achieve an ideal TT/Tri position. Any guesses? Well, it can’t be more than a few centimeters, right? Let’s find out just how much I’d have to move forward…
First, I took some video of me pedaling on the road bike in a powerful “hoods” position – I’d ride like this if I was doing a long climb or something. I grabbed a frame from this video with my foot in the maximum extended position and digitized some joints, along with an outline of my back/head, as shown below:
In my fancy schmancy CAD program (OK, I lied, it’s not very fancy…) I scaled the image appropriately, and then proceeded to rotate the dots/spline around the BB until my head was below the peak point of my back into what looks like an aero TT position.
As you can see, the green outline/red dots are where I started, and the blue outline/green dots are where I ended up after being rotated around the BB. Looks like a pretty good TT position, doesn’t it… Those accompanying numbers/dimensions are approximately how much I’d have to move the saddle forward and up in order to accomplish this rotation without affecting the magic hip angle. Yes, that would be approximately 25.5cm forward, and 6 cm up. Does this sound reasonable to y’all? For this caveman, it doesn’t really pass the smell test – especially once one considers production TT/Tri bike geometry.
In this new position, one has preserved the hip angle, but at what cost? And is it any more aerodynamic than what could be achieved via other setups? Well, it depends…
It should be noted that the relationship between the powerful pushing muscles of the leg/knee and the pedal spindle have not been preserved. Which is better – preserved hip angle, or preserved knee/spindle relationship? Fact of the matter is that “it depends”.
In my case, I evaluated a forward position (~11cm forward of the road position, and subsequently a tighter hip angle than my hoods position) last year for around 8 weeks. I didn’t go any faster than I did before the test. But why not? Was it because my hip angle changed and I lost power? Well, considering that when I ride in the drops, I look like this (much tighter hip angle, eh?)
I’m gonna have to vote for “not much” of a decrease in power production due to hip angle change – I can put out the same watts in the drops that I can on the hoods (or so says the SRM power meter)!. You might be different, though. Maybe I didn’t get any faster because my aerodynamics didn’t appreciably change. That’s a possibility, especially judging by the interesting stuff I’ve seen in the wind tunnel these past few months. So, is “forward faster”? Not necessarily, but “faster is faster” all the time.
Thank goodness there are tools available out there that let the individual assess these tradeoffs between power and aerodynamics. In the realm of power production, there exists on bike power meters. In the realm of aerodynamics there exists frontal area measurement, field testing, and wind tunnel testing. The maximization of watts produced divided by CxA (a measure of aerodynamics) is what will determine flat TT/Triathlon bike speed. In a nutshell, there are tools that will help guide you along the way to a faster bike fit. Since this is true, you can evaluate for yourself whether or not “faster is faster” – I’m sure we’ll agree on this one, though.
In closing, the next time you are obsessing about whether or not you should move the saddle forward 1-2cm for your TT position, remember the number 25.5 – because that’s how much I’d have to move the saddle forward to do it right. If you ask me, dorkin’ around with a few cm of saddle position is just so much fartin’ in the wind. Do it, don’t do it, knock yourself out. Sooner or later, you’re gonna have to bend over anyways. Don’t take my word for it, though, use the right performance tools for the job and find out for yourself whether or not “faster is faster”!