Tri bike geometry: weight forward = bad handling?

andresmuro@aol.com

On May 27, 3:29 pm, "joseph.santanie...@gmail.com"
<joseph.santanie...@gmail.com> wrote:
> On May 27, 6:47 pm, "Jeff Potter (of OutYourBackdoor.com)"
>
>
>
> <Jeff...@hotmail.com> wrote:
> > I'm curious about tri bike geometry.
>
> > It seems that putting an aerobar on a regular road bike ends up
> > putting more rider weight forward. This likely changes bike handling
> > quite a bit.
>
> > When I ride with an aerobar I move my seat up a half inch and forward
> > an inch. I also tilt the nose down. --This also indicates that my
> > weight has moved forward.
>
> > So how do tri-specific bikes deal with this?
>
> > Do they change the bike geometry to move the rider rearward for a
> > given wheelbase to make up for the forward-weight? (How do they do
> > that? Shorter stays, curved seat-tube, LONGER top tube, shorter stem?)
> > I see that at least the Cervelo offers a steeper seat-tube---which
> > would put rider weight more forward unless other changes offset it.
>
> > (What is the ideal weight ratio on the wheels anyway? I recall that
> > it's 50-50 but who knows.)
>
> > Weight ratio and C of G would also affect how a bike responds to
> > braking. --It would seem that aerobars put weight forward AND raise
> > the CoG causing a bike that would do an endo if braked hard.
>
> > Also, does the front geometry change? I would think that if a position
> > had more weight forward that one might want a low-trail fork. Long-
> > trail is often associated with fork-flop which is increased with added
> > weight on the front-end. --This means that small changes in body
> > position on an aerobar would cause a bike to wobble going down the
> > road. But long-trail is also associated with race bikes. While low-
> > trail is known mostly in French long distance touring circles---for
> > bikes with loaded handlebar bags, especially.
>
> > Do tri-bikes have longer wheelbase? --They don't have fast handling
> > needs.
>
> > Here's a webpage for the geometry of a Cervelo:http://www.cervelo.com/bikes.aspx?bike=P2C2008#G
>
> > Offhand, it looks like they don't do much special for geometry other
> > than throwing rider weight forward. It looks like they have a slack
> > head-tube angle---which would really increase fork flop with a long-
> > trail fork
>
> > Just wondering...
>
> > --JP
> > allbikemag.com
> > outyourbackdoor.com
>
> I have recently switched from a road bike frame kitted out as a TT
> bike to a real TT bike frame. The front-center (bb to front axle) is
> much longer (12cm maybe?) on th eTT frame and the handling is MUCh
> better. I'm on the big side, so I think perhaps using a road bike with
> a forward aero position was extra sub-optimal in terms of weight
> distribution.
>
> Joseph

I have ridden both road bikes (with saddle forward) and TT bikes and
they both handle fine to me. For me personaly, I prefer a Tri bike set
up as a road bike, than a traditional road bike. My regular road bike
has a 76 degree seat angle. It is the best improvement that I could
have ever done to my riding. I used to always get a sore lower back
after riding more than two hours hard. Since I moved to a steep angled
road bike, I have never had sore lower backs and I can ride for hours
non-stop. In fact, I can also comfortably ride on aerobars for hours
on end with no bother to my back.

I have both a road and tri bike, and use them both interchangeably. If
I'll be doing lots of hills or riding with a big group, I'll stick to
my roadie. For long flat rides or rides with a smaller group of people
I use the tri bike. They are both equally as comfortable and handle
just a nice. The tri bike is of course faster because of the
aerobars.

The advantage of the tri bike geometry is that when your knee comes
up, your hamstring muscles is not in as steep an angle with respect to
your lower back. So, they are not pulling against your lower back as
much. If you ride about two hours or less, this is no big deal.
However, If you like to be on your bike for over three hours, this is
a blessing.

Another thing I found about aerobars is that being being the lowest
possible is not necessarily the best strategy. You want to reach a
compromise between low and narrow. If you try to go to low, your
handling worsens, it is hard to breath, and can be very painful. If
you bring your arms together, you have much better control pf your
bike and you gain a lot in terms of aerodynamics. My aerobar position
in no lower than when I grab the drops on my roadbike. However, my
shoulders are tucked in and my elbows come pretty close together. You
need to develop good shoulder flexibility to do this. But, once you
manage that you'll have great control over you bike.

Andres