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Tri bike geometry: weight forward = bad handling?



 
 
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  #1  
Old May 28th 08, 12:33 AM posted to rec.sport.triathlon,rec.bicycles.tech
Phil Holman
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Posts: 5
Default Tri bike geometry: weight forward = bad handling?


"Jeff Potter (of OutYourBackdoor.com)" wrote in
message
...
On May 27, 5:29 pm, "
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


  #2  
Old May 28th 08, 12:47 AM posted to rec.sport.triathlon,rec.bicycles.tech
Tom Kunich
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Posts: 4
Default Tri bike geometry: weight forward = bad handling?

"Phil Holman" [email protected] wrote in message
. ..

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.

  #3  
Old May 28th 08, 05:53 AM posted to rec.sport.triathlon,rec.bicycles.tech
Phil Holman
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Posts: 5
Default Tri bike geometry: weight forward = bad handling?


"Jeff Potter (of OutYourBackdoor.com)" wrote in
message
...
On May 27, 6:47 pm, "Tom Kunich" [email protected] com wrote:
"Phil Holman" [email protected] wrote in message

. ..



[ ]. 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


  #5  
Old May 29th 08, 02:40 AM posted to rec.sport.triathlon,rec.bicycles.tech
Phil Holman
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Posts: 5
Default Tri bike geometry: weight forward = bad handling?


"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


  #6  
Old May 29th 08, 04:10 AM posted to rec.sport.triathlon,rec.bicycles.tech
jim beam
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Posts: 2
Default Tri bike geometry: weight forward = bad handling?

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

  #7  
Old May 29th 08, 09:07 PM posted to rec.sport.triathlon,rec.bicycles.tech
Booker Bense
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Posts: 1
Default Tri bike geometry: weight forward = bad handling?

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


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.


I think "as good as the rules allow" would be closer to the
facts. See Chris Boardman and the superman position.

_ Booker C. Bense
  #9  
Old October 24th 12, 12:37 PM
Triaironman Triaironman is offline
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First recorded activity by FitnessBanter: Oct 2012
Posts: 12
Default

Quote:
Originally Posted by williamthatcher View Post
I believe you should get the one with better handling. The extra bux you spend for the handling will be important when you're in the race already. Handling is always better than speed for me.
I actually prefer to go fast and have a slightly sketchy bike than be slow....althought hat might bite me int he arse someday! Obviously it needs to handle okay as on long downhills you need something that works...TT bikes are renowned for being worse handling than road bikes especially on technical courses but if you are doing middle to long distance triathlons then a TT bike is a must - not only because of the time saved but also because of the different muscles used because you are above or in front of the BB. Having the ST more than 76% or so saves your legs for the run which is so important!
 




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