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Faster is Faster.
5/31/2005
Words and images by: Kraig Willett
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?
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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.
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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 CdA (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”!
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