J
Jeff Potter (of OutYourBackdoor.com)
Guest
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
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