Tri bike geometry: weight forward = bad handling?

On Wed, 28 May 2008 08:12:55 +0100,
wrote:



When I say my TT frame bike is better handling, I mean it is more
stable and just feels more balanced. It isn't nimble or anything, but
I do feel better riding fast with it for example down hill. And around
turns. So I can stay in the aero bars through more stuff than I was
comfortable doing with ethe road bike frame.

That makes sense. I never understood the old-tme fad for short wheelbase
TT bikes, and vaguely remember a quote about short skis and Richard Nixon
that seems fitting "... they will not take you exactly where you want to
go and their speed is only in diverting movements, not on velocity."

(Yikes. --Nothing I wrote suggests a desire for TT bikes that are like
crit bikes. , stable and steady would be fine. --I doubt that
torsional stiffness is the culprit behind most bad TT handling. --
Remove aerobars...good one, Ryan! ...Not a TT rider, I gather.)

So, does anyone here have a sense (based on knowledge and experience)
for how changing the design of a TT frame might affect handling? I
suggest changes that lower the CoG and move it rearward. Also changes
that might improve handling---and ability to ride a straight line when
in aerobars. I wonder what those changes might be? Any thoughts
(based on knowledge/experience, that is) on fork trail in this regard?

I'm wondering if short stays, lower BB (lower saddle), curved/steep
ST, long TT, short stem, handlebar with elbow rests as low as comfy,
and a low-trail fork might add up up to something interesting...
Anyone ever see a bike like that?

To keep it simpler: Anyone know of a low-trail TT bike?

Anyone know of a curved/steep ST TT bike with long TT?

--JP
allbikemag.com

Tri as we might, we go off track.

The OP started by asking about a tri bike, one for triathlons.
Different optimization than for a TT, a time trial. The positioning on
the tri bike is not only aero, with fine handling be damned-- as rules
are that you are near nobody's wheel-- but, most importantly that you
save the muscles you'll need for running.

Harry Travis
USA

On May 28, 8:32 am, "Jeff Potter (of OutYourBackdoor.com)"
wrote:
(Yikes. --Nothing I wrote suggests a desire for TT bikes that are like
crit bikes. , stable and steady would be fine. --I doubt that
torsional stiffness is the culprit behind most bad TT handling. --
Remove aerobars...good one, Ryan! ...Not a TT rider, I gather.)

So, does anyone here have a sense (based on knowledge and experience)
for how changing the design of a TT frame might affect handling? I
suggest changes that lower the CoG and move it rearward. Also changes
that might improve handling---and ability to ride a straight line when
in aerobars. I wonder what those changes might be? Any thoughts
(based on knowledge/experience, that is) on fork trail in this regard?

I'm wondering if short stays, lower BB (lower saddle), curved/steep
ST, long TT, short stem, handlebar with elbow rests as low as comfy,
and a low-trail fork might add up up to something interesting...
Anyone ever see a bike like that?

To keep it simpler: Anyone know of a low-trail TT bike?

Anyone know of a curved/steep ST TT bike with long TT?

On May 28, 2:32*pm, "Jeff Potter (of OutYourBackdoor.com)"
wrote:
(Yikes. --Nothing I wrote suggests a desire for TT bikes that are like
crit bikes. , stable and steady would be fine. --I doubt that
torsional stiffness is the culprit behind most bad TT handling. * --
Remove aerobars...good one, Ryan! ...Not a TT rider, I gather.)

So, does anyone here have a sense (based on knowledge and experience)
for how changing the design of a TT frame might affect handling? I
suggest changes that lower the CoG and move it rearward. Also changes
that might improve handling---and ability to ride a straight line when
in aerobars. I wonder what those changes might be? *Any thoughts
(based on knowledge/experience, that is) on fork trail in this regard?

I'm wondering if short stays, lower BB (lower saddle), curved/steep
ST, long TT, short stem, handlebar with elbow rests as low as comfy,
and a low-trail fork might add up up to something interesting...
Anyone ever see a bike like that?

To keep it simpler: Anyone know of a low-trail TT bike?

Anyone know of a curved/steep ST TT bike with long TT?

--JP
allbikemag.com

I wouldn't want to monkey with trail on a TT bike. Those bikes can see
a wide range of speeds, and I'd like my handling to be neutral to
avoid unpleasant surprises.

I think fore-aft weight balance is important. That's why bikes with
steep seat-tubes need the head tube moved forward at least a
corresponding amount. This increases the front-center which keeps the
weight balance reasonable.

You want the steep seat-tube to be able to get the seat forward, so
you can have a flat back without having to overdo the hip angle. Then
you want the top-tube to be long enough to put the front wheel out
where it needs to be. A short-ish stem decreases the tiller effect on
steering and maybe makes it feel more stable.

I have a $139 TT frame from leaderbikeusa.com that I have zero
problems riding in a straight line. It has a top-tube about the same
length as my road bike, but since the seat-tube is much steeper, the
front end is much further forward. I run a short 6cm stem, while I use
a 12 on my road bike.

Joseph

On May 28, 4:36 pm, "
wrote:
[ ]
I wouldn't want to monkey with trail on a TT bike. Those bikes can see
a wide range of speeds, and I'd like my handling to be neutral to
avoid unpleasant surprises.

The thing is, to have "neutral" handling with a bike that has a
forward position might require a low trail fork. The common race bike
has a long trail fork which makes a bike sensitive to front-end weight
shifts as might happen often when riding on aerobars.

I have a $139 TT frame from leaderbikeusa.com that I have zero
problems riding in a straight line. It has a top-tube about the same
length as my road bike, but since the seat-tube is much steeper, the
front end is much further forward. I run a short 6cm stem, while I use
a 12 on my road bike.

Sounds like a good start!

I'm no fork-trail expert but I think it's part of the equation to give
a stable bike. Different-use bikes need different trails but my
impression is that modern race-bike trail is somewhat of an ignored
issue. Kind of one size fits all.

--JP
allbikemag.com

On May 28, 4:19 pm, "
wrote:
Tri as we might, we go off track.

The OP started by asking about a tri bike, one for triathlons.
Different optimization than for a TT, a time trial. The positioning on
the tri bike is not only aero, with fine handling be damned-- as rules
are that you are near nobody's wheel-- but, most importantly that you
save the muscles you'll need for running.

I think they have similar issues, but you're right, a tri bike has a
more open position. It also has to handle better as tri's are on more
diverse courses than typical TT's, which are often out'n'back.

--JP
allbikemag.com

"Jeff Potter (of OutYourBackdoor.com)" wrote in
message
...
(Yikes. --Nothing I wrote suggests a desire for TT bikes that are like
crit bikes. , stable and steady would be fine. --I doubt that
torsional stiffness is the culprit behind most bad TT handling. --
Remove aerobars...good one, Ryan! ...Not a TT rider, I gather.)

So, does anyone here have a sense (based on knowledge and experience)
for how changing the design of a TT frame might affect handling? I
suggest changes that lower the CoG and move it rearward. Also changes
that might improve handling---and ability to ride a straight line when
in aerobars. I wonder what those changes might be? Any thoughts
(based on knowledge/experience, that is) on fork trail in this regard?

I'm wondering if short stays, lower BB (lower saddle), curved/steep
ST, long TT, short stem, handlebar with elbow rests as low as comfy,
and a low-trail fork might add up up to something interesting...
Anyone ever see a bike like that?

To keep it simpler: Anyone know of a low-trail TT bike?

Anyone know of a curved/steep ST TT bike with long TT?

You seem to have have conflicting requirements....ride a straight line
and low-trail for one.

Phil H

On May 28, 8:40 pm, "Phil Holman" piholmanc@yourservice wrote:
"Jeff Potter (of OutYourBackdoor.com)" wrote in
...



(Yikes. --Nothing I wrote suggests a desire for TT bikes that are like
crit bikes. , stable and steady would be fine. --I doubt that
torsional stiffness is the culprit behind most bad TT handling. --
Remove aerobars...good one, Ryan! ...Not a TT rider, I gather.)

So, does anyone here have a sense (based on knowledge and experience)
for how changing the design of a TT frame might affect handling? I
suggest changes that lower the CoG and move it rearward. Also changes
that might improve handling---and ability to ride a straight line when
in aerobars. I wonder what those changes might be? Any thoughts
(based on knowledge/experience, that is) on fork trail in this regard?

I'm wondering if short stays, lower BB (lower saddle), curved/steep
ST, long TT, short stem, handlebar with elbow rests as low as comfy,
and a low-trail fork might add up up to something interesting...
Anyone ever see a bike like that?

To keep it simpler: Anyone know of a low-trail TT bike?

Anyone know of a curved/steep ST TT bike with long TT?

You seem to have have conflicting requirements....ride a straight line
and low-trail for one.

Phil H

Are you familiar with how trail affects handling? of bikes with
different uses?,

Low trail is known to make a front-weighted bike easy to ride straight
with, for instance. Low trail was used by the French for bikes with
front handlebar bags or loaded front-ends, like newspaper bikes with
loaded baskets. So it makes me wonder if TT/tri bikes would benefit as
well. Who knows? It would take experience to inform us. Has anyone
here ridden a low-trail bike with aerobars?

--JP
allbikemag.com

Jeff Potter (of WhatYourBackdoor???.com) wrote:
On May 28, 4:36 pm, "
wrote:
[ ]
I wouldn't want to monkey with trail on a TT bike. Those bikes can see
a wide range of speeds, and I'd like my handling to be neutral to
avoid unpleasant surprises.

The thing is, to have "neutral" handling with a bike that has a
forward position might require a low trail fork. The common race bike
has a long trail fork which makes a bike sensitive to front-end weight
shifts as might happen often when riding on aerobars.

I have a $139 TT frame from leaderbikeusa.com that I have zero
problems riding in a straight line. It has a top-tube about the same
length as my road bike, but since the seat-tube is much steeper, the
front end is much further forward. I run a short 6cm stem, while I use
a 12 on my road bike.

Sounds like a good start!

I'm no fork-trail expert but I think it's part of the equation to give
a stable bike. Different-use bikes need different trails but my
impression is that modern race-bike trail is somewhat of an ignored
issue.

like the stability benefits of greater torsional stiffness afforded by
bigger diameter tubes?



Kind of one size fits all.

--JP
allbikemag.com

In article
,
"Jeff Potter (of OutYourBackdoor.com)" wrote:

(Yikes. --Nothing I wrote suggests a desire for TT bikes that are like
crit bikes. , stable and steady would be fine. --I doubt that
torsional stiffness is the culprit behind most bad TT handling. --
Remove aerobars...good one, Ryan! ...Not a TT rider, I gather.)

Am so. Just really bad at it:

http://escapevelocity.bc.ca/2008/warpspeedresults

I seem to spend a lot of time making self-indulgent points in newsgroups
and then explaining my tortured logic later, but here it is:

Aero bars involve, ideally, a position that has exchanges sensible
positioning with good control for one that has optimal aerodynamics.

Further requesting that said aero position offer stable handling is
trying to make a bakfiets out of a sow's ear.

In my experience, TT bikes are good enough. They're probably close to
being as good as possible, given the number of professionals with an
incentive to make them better.

So, does anyone here have a sense (based on knowledge and experience)
for how changing the design of a TT frame might affect handling? I
suggest changes that lower the CoG and move it rearward. Also changes
that might improve handling---and ability to ride a straight line when
in aerobars. I wonder what those changes might be? Any thoughts
(based on knowledge/experience, that is) on fork trail in this regard?

I'm wondering if short stays, lower BB (lower saddle), curved/steep
ST, long TT, short stem, handlebar with elbow rests as low as comfy,
and a low-trail fork might add up up to something interesting...
Anyone ever see a bike like that?

That sounds like a formula for adding as much weight to the bars as
possible. That doesn't seem like a great plan. There are (as you
elsewhere note) bikes designed to accommodate large amounts of weight on
front racks, but that's rarely the best plan.

To keep it simpler: Anyone know of a low-trail TT bike?

Anyone know of a curved/steep ST TT bike with long TT?

http://velospace.org/node/10599

--
Ryan Cousineau http://www.wiredcola.com/
"In other newsgroups, they killfile trolls."
"In rec.bicycles.racing, we coach them."