Tri bike geometry: weight forward = bad handling? - Triathlon Week

05-27-2008, 10:28 PM

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:
[Only registered and activated users can see links. ]

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

05-27-2008, 10:28 PM

On May 27, 6:47*pm, "Jeff Potter (of OutYourBackdoor.com)"
<[Only registered and activated users can see links. ]> 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:[Only registered and activated users can see links. ]
>
> 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

05-27-2008, 10:28 PM

On May 27, 5:29 pm, "[Only registered and activated users can see links. ]"
<[Only registered and activated users can see links. ]> wrote:

> 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.

Ah! Interesting. So...Cervelo notes that their steeper ST gives a
shorter TT. Hmmm, that would make for a shorter front end, I would
think. It sounds like your new TT bike has a longer TT---which
indicates that the designer of your bike is pushing your weight ratio
rearward where it belongs---for someone on aerobars. So it would seem.
Let's see what the experts have to say here...

JP

05-27-2008, 10:28 PM

"Jeff Potter (of OutYourBackdoor.com)" <[Only registered and activated users can see links. ]> wrote in
message
news:[Only registered and activated users can see links. ]...
> On May 27, 5:29 pm, "[Only registered and activated users can see links. ]"
> <[Only registered and activated users can see links. ]> wrote:
>
>> 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.
>
> Ah! Interesting. So...Cervelo notes that their steeper ST gives a
> shorter TT. Hmmm, that would make for a shorter front end, I would
> think. It sounds like your new TT bike has a longer TT---which
> indicates that the designer of your bike is pushing your weight ratio
> rearward where it belongs---for someone on aerobars. So it would seem.
> Let's see what the experts have to say here...
>
IMO frame priorities are to get the seat forward and over the BB and to
be as aero as possible (lower on the front). Weight distribution and
thus handling are minor considerations in a TT because, for the most
part, you're riding on your own. Just as well because riding on the
aerobars far overshadows an other handling characteristic.

Phil H

05-27-2008, 10:28 PM

"Phil Holman" <piholmanc@yourservice> wrote in message
news:[Only registered and activated users can see links. ]. ..
>
> IMO frame priorities are to get the seat forward and over the BB and to be
> as aero as possible (lower on the front). Weight distribution and thus
> handling are minor considerations in a TT because, for the most part,
> you're riding on your own. Just as well because riding on the aerobars far
> overshadows an other handling characteristic.

I think that handling per se' isn't much of a problem on a TT bike. The
reason that Tri-bikes have a forward seat tube is because runners don't bend
at the waist as easily as riders. When you shove the runner/rider forward on
a Tri-bike the front wheel weight STILL doesn't get an overload. It just
feels different and isn't negative as such.

Small people on small bikes that mount 700c wheels are simply stuck not
being able to get very aero. Larger riders can always use short head tube
bikes and get low enough.

Frontal area, coefficient of friction and rolling resistance are the
important items and handling isn't that much of a problem - once you get
used to the way a particular bike handles you can modify your style to it.

05-27-2008, 10:28 PM

On May 27, 6:47 pm, "Tom Kunich" <cyclintom@yahoo. com> wrote:
> "Phil Holman" <piholmanc@yourservice> wrote in message
>
> news:[Only registered and activated users can see links. ]. ..
>
>
>
> > [ ]. Weight distribution and thus
> > handling are minor considerations in a TT because, for the most part,
> > you're riding on your own. Just as well because riding on the aerobars far
> > overshadows an other handling characteristic.
>
> I think that handling per se' isn't much of a problem on a TT bike. [ ]

I'm not convinced. I suggest looking into this further. People who
spend big bux on bix should get great handling no matter what position
they're in. That's how I'd sell my pricey bikes anyway if I was
buildin' 'em. There's probably a way to have an aero/forward position
while still having great handling. Handling is CRITICAL ALWAYS in my
view. Emergencies come up ALL THE TIME on race courses. Courses are
tricky. "Stuff" happens while out training. ZERO excuse for not having
a great-handling bike. Anyway, if you wanted a great handling aerobar
bike, what would you do?

--JP

05-27-2008, 10:28 PM

Jeff Potter (of OutYourBackdoor.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:
> [Only registered and activated users can see links. ]
>
> 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
>
>

is this frame of yours steel? does it have standard diameter tubes?

if so, consider moving to an aluminum frame with big tube diameter - the
better torsional stiffness makes for a much more stable ride.

05-27-2008, 10:28 PM

"Jeff Potter (of OutYourBackdoor.com)" <[Only registered and activated users can see links. ]> wrote in
message
news:[Only registered and activated users can see links. ]...
> On May 27, 6:47 pm, "Tom Kunich" <cyclintom@yahoo. com> wrote:
>> "Phil Holman" <piholmanc@yourservice> wrote in message
>>
>> news:[Only registered and activated users can see links. ]. ..
>>
>>
>>
>> > [ ]. Weight distribution and thus
>> > handling are minor considerations in a TT because, for the most
>> > part,
>> > you're riding on your own. Just as well because riding on the
>> > aerobars far
>> > overshadows an other handling characteristic.
>>
>> I think that handling per se' isn't much of a problem on a TT bike.
>> [ ]
>
> I'm not convinced. I suggest looking into this further. People who
> spend big bux on bix should get great handling no matter what position
> they're in.

Define "great handling" for a TT bike?

>That's how I'd sell my pricey bikes anyway if I was
> buildin' 'em. There's probably a way to have an aero/forward position
> while still having great handling. Handling is CRITICAL ALWAYS in my
> view. Emergencies come up ALL THE TIME on race courses. Courses are
> tricky. "Stuff" happens while out training. ZERO excuse for not having
> a great-handling bike. Anyway, if you wanted a great handling aerobar
> bike, what would you do?

Sounds like you want a TT bike that handles like a crit or mass start
track bike. Good luck with that.

Phil H

05-28-2008, 10:53 PM

On May 28, 2:22*am, "Jeff Potter (of OutYourBackdoor.com)"
<[Only registered and activated users can see links. ]> wrote:
> On May 27, 6:47 pm, "Tom Kunich" <cyclintom@yahoo. com> wrote:
>
> > "Phil Holman" <piholmanc@yourservice> wrote in message
>
> >news:[Only registered and activated users can see links. ] ...
>
> > > [ *]. Weight distribution and thus
> > > handling are minor considerations in a TT because, for the most part,
> > > you're riding on your own. Just as well because riding on the aerobarsfar
> > > overshadows an other handling characteristic.
>
> > I think that handling per se' isn't much of a problem on a TT bike. [ *]
>
> I'm not convinced. I suggest looking into this further. People who
> spend big bux on bix should get great handling no matter what position
> they're in. That's how I'd sell my pricey bikes anyway if I was
> buildin' 'em. There's probably a way to have an aero/forward position
> while still having great handling. Handling is CRITICAL ALWAYS in my
> view. Emergencies come up ALL THE TIME on race courses. Courses are
> tricky. "Stuff" happens while out training. ZERO excuse for not having
> a great-handling bike. Anyway, if you wanted a great handling aerobar
> bike, what would you do?
>
> --JP

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.

Joseph

05-28-2008, 10:54 PM

On Wed, 28 May 2008 08:12:55 +0100, [Only registered and activated users can see links. ]
<[Only registered and activated users can see links. ]> 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."

05-28-2008, 10:54 PM

In article
<[Only registered and activated users can see links. ]>,
"Jeff Potter (of OutYourBackdoor.com)" <[Only registered and activated users can see links. ]> wrote:

> On May 27, 6:47 pm, "Tom Kunich" <cyclintom@yahoo. com> wrote:
> > "Phil Holman" <piholmanc@yourservice> wrote in message
> >
> > news:[Only registered and activated users can see links. ]. ..
> >
> >
> >
> > > [ ]. Weight distribution and thus
> > > handling are minor considerations in a TT because, for the most part,
> > > you're riding on your own. Just as well because riding on the aerobars far
> > > overshadows an other handling characteristic.
> >
> > I think that handling per se' isn't much of a problem on a TT bike. [ ]
>
> I'm not convinced. I suggest looking into this further. People who
> spend big bux on bix should get great handling no matter what position
> they're in. That's how I'd sell my pricey bikes anyway if I was
> buildin' 'em. There's probably a way to have an aero/forward position
> while still having great handling. Handling is CRITICAL ALWAYS in my
> view. Emergencies come up ALL THE TIME on race courses. Courses are
> tricky. "Stuff" happens while out training. ZERO excuse for not having
> a great-handling bike. Anyway, if you wanted a great handling aerobar
> bike, what would you do?

Remove the aerobars.

--
Ryan Cousineau [Only registered and activated users can see links. ] [Only registered and activated users can see links. ]
"In other newsgroups, they killfile trolls."
"In rec.bicycles.racing, we coach them."

05-28-2008, 10:54 PM

(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

05-28-2008, 10:54 PM

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)"
<[Only registered and activated users can see links. ]> 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?
>

05-28-2008, 10:54 PM

On May 28, 2:32*pm, "Jeff Potter (of OutYourBackdoor.com)"
<[Only registered and activated users can see links. ]> 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

05-28-2008, 10:54 PM

On May 28, 4:19 pm, "[Only registered and activated users can see links. ]" <[Only registered and activated users can see links. ]>
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