Hi Jose,
>
> Seat tube angle determines how effectively long a cantilever the
> seatpost acts as; with steel seatposts, it's possible to see these flex
> with weight. The steeper the seat tube angle (ie the closer to
> vertical), the less flex possible for the seatposts. How much this is a
> factor with Al posts, I'm unsure.
>
Ahhhh... The flexible seatpost widget made famous by the Moots Ti
Laidback post, a rather expensive piece of placebo effective toy.
Sure, a thing like this would bend a little since the thing has quite a
bit of setback, but you need to set it back a lot and have it stuck all
the way out to have any noticeable effect.
And seat tube angle "DOES NOT" determine how effective long this action
does.. A seat tube angle determines how "LOW or HIGH" you as a rider
can ride your bike.. Problem with a normal 73-74 degrees road bike is
that, to get super low and as super flat as your back can get, you need
to move your saddle very forward. This does 2 bad things.
1, You're moving more of your weight to the front (road bike design was
supposed to distribute equal weight between front and back), so
steering stability will be compromised.
2, Increase hip angle and steep back curvature which will cause a
number of very nasty side effects, and not to mention pain.. Now, very
few people can ride in this very very low and steep geometry. I
can't..
To correct these problems, the seat tube angle need to be steepened to
correct problem number 2, plus the chainstays need to be shortened to
bring the rear wheel closer to the butt of the rider to correct problem
number 1. So if you choose a steep tube angled bike, you will have
very short chainstays.
>
> I don't see what this has to do with comfort. If you fix the seat tube
> angle, the rest of the geometry will have to conform to place the rider
> in the best position and fit possible. The terms "tri" or "classic
> road" fronts don't make sense, since there aren't set values for these.
>
In a muscle-supported posture, we are mostly concerned about the proper
hip and shoulder angles.
Shoulder angles should be around 90 degrees more or less, very relaxed
as it should be and the hip angle should also be around 90 degrees or
less. This is a very good aero well balanced riding position.
Changing the seat tube angle essentially "corrects" the offset created
by the displacement of the saddle. Rule of thumb is this.. Want to go
lower on the bars, you move forward. Want to higher on the bars, you
move backwards. If you don't do this, hip angle will either be way too
steep (you'll break your back doing that) or way too shallow (riding
like a newbie).
> > A regular road bike is made with a proven geometry that is made to do
> > well in everything.
>
> Proven geometry for whom? The variations in frame dimensions available
> among different brands of bicycles puts this claim to the test, as well
> as the popularity of custom frames.
>
More than hundreds of years of fine tuning, the diamond shaped road
bike is a proven geometry. Any changes made by any manufacturer from
the basic design are made specific for the application it was meant to
serve.
A word about custom frames..
Custom frames are nice, but they are popular not because they solve the
fitting problem (few do), they are so because you can customize them to
whatever you want the bike to be. Great if you have lots of moolah!
Not so great if you don't..
Seriously, we have SO MANY frame selections that I doubt any bike
fitter would have any problems fitting anyone.. The problem is with
brand recognition. Now, if all the frames are painted white or black,
we wouldn't need custom frames. In reality however, people want to own
good brands. It's reality and I think that's fair.
People try to own a piece of brand name, be it Seven, Colnago,
Marinoni, Trek Project One, and on and on and on. Nothing wrong with
that, except it projects a sort of illusion to others that if none of
these bikes fit you, go custom.
> Huh? The rider's geometry can't be changed! Your arms, torso and legs
> are going to be that way unless you're still growing.
>
Read my explanation about hip angle and seat tube angle again which
deals with riding geometry.
>
> Except that drop bars actually make you change your position, depending
> on which part of the bar you're holding on to. Many people claim that
> it's this ability to choose hand holds and posture which makes drop bars
> attractive for them.
>
Change your hip angle and butt to saddle position -- yes. Position --
no, because any 3 positions you place your hands on the drop bar
shouldn't make any drastic changes to the upper body shoulder angle,
assuming the bike is professionally fitted and the width of the
handlebar matches the shoulder's width of the rider. Hands on the
hoods should be your neutral position. So, when you go to the drops,
your hip angle steepens but still manageable and you need to bend your
neck up more, but nothing should drastically change on your upper body.
As you move your hands towards the flat portion of the drop bars,
you'll scoot your butt back a bit since the flat portion are further
back than the hoods, closer to the rider. This position, however, is
great for climbing. In fact, the further backward you sit on the
saddle, the more power you can leverage on the pedals.
David.
