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Longtitudinal saddle position



 
 
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  #1  
Old March 17th 04, 07:30 PM
DavidR
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Default Longtitudinal saddle position

I am trying to buy a replacement stem for a friend that has changed his
drops for butterflies and agonising over the correct size. It is on a Galaxy
which has a 110mm stem. The butterfly shape takes it +70 -100 mm from the
stem.

St John's Street has 150mm and 175mm stems. I am worried about getting a
150 in case it is still too short. My inclination is to go for the 175 and
move the saddle forward if it is too long .

My friend then showed me all the books that that say the saddle should be
set so that there is a plumb line between knee and pedal. Eh? All I have
ever done is move the saddle so that I sit on it properly.

I have gone and checked my bikes. I have a tourer with the saddle fully back
and according to the plumb it is about 30mm too far forward. My mtb has a
longer frame so the saddle is slightly further forward with consequent
different relationship with the BB.

I also have a road bike. Now, this has a much steeper frame and I have the
saddle fully forward (I am getting a shorter stem for this one) which puts
it about 80mm nearer the BB compared to the tourer.

Firstly, what can others suggest about the choice of stem for these
butterflies. Secondly, do others put much score on the business of
longitudinal position?


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  #2  
Old March 18th 04, 05:51 AM
Pete Biggs
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Default Longtitudinal saddle position

DavidR wrote:
I am trying to buy a replacement stem for a friend that has changed
his drops for butterflies and agonising over the correct size. It is
on a Galaxy which has a 110mm stem. The butterfly shape takes it +70
-100 mm from the stem.

St John's Street has 150mm and 175mm stems. I am worried about
getting a 150 in case it is still too short.


I don't have experience of butterfly bars but I wouldn't expect such a
long stem to be required, necessarily, despite the bars having a negative
reach, as a more upright position is bound to be desired. Stems longer
than 140mm are unusual on any kind of bike with any kind of bars. You
have to start worrying about flex and strength once you get beyond that.

In any case, you might want to consider the double-articulated Look
ErgoStem. Expensive and heavy but extremely versatile. Reach goes up to
160mm (when rise is zero). A shim will be required for 25.4 bars.

My inclination is to go
for the 175 and move the saddle forward if it is too long .

My friend then showed me all the books that that say the saddle
should be set so that there is a plumb line between knee and pedal.


That's rubbish. Search the web for "The myth of KOPS", etc. However, it
is important that the saddle should be set for comfortable seating and
pedalling (that's usually back a bit, whatever the stem is), not adjusted
to correct reach to the bars. That's what the top tube, stem and bars are
for.

~PB


  #3  
Old March 18th 04, 10:45 AM
McBain_v1
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Default Longtitudinal saddle position

Davidr wrote:
My friend then showed me all the books that that say the saddle should
be set so that there is a plumb line between knee and pedal. Eh? All I
have ever done is move the saddle so that I sit on it properly. ...do
others put much score on the business of longitudinal position?



Yeah, I'd second what Pete Biggs wrote about the KOPS (Knee Over Peda
Spindle) business. Lots of people advocate this as being critical t
effective cycling performance, but I'd take comfort any day

Saddle position is important from a comfort point of view. There ar
lots of bizarre formulae out there that will dictate how you "should
set up your bike. I doubt you'd get a consistent answer if you trie
each and every one of them

As for a 175mm stem - that seems overlong to me for a roadbike frame.
only use a 130mm quill stem (just cannot bring myself to give up my 631
steel frame), but I haven't seen may stems that go beyond the 140m
length on the Ahead designs


-


  #4  
Old March 18th 04, 05:53 PM
iarocu
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Default Longtitudinal saddle position

"DavidR" wrote in message ...
snipped
My friend then showed me all the books that that say the saddle should be
set so that there is a plumb line between knee and pedal. Eh? All I have
ever done is move the saddle so that I sit on it properly.

I have gone and checked my bikes. I have a tourer with the saddle fully back
and according to the plumb it is about 30mm too far forward. My mtb has a
longer frame so the saddle is slightly further forward with consequent
different relationship with the BB.



http://www.peterwhitecycles.com/fitting.htm
The above article bike fitting by Peter White, a USA cycle dealer is
the best I,ve seen on bike fit. The section on fore/aft saddle
position is pasted below.
" Fore-Aft Saddle Position

Now we get to what I think is the most important part of fitting a
bicycle, the fore-aft position of the saddle. Once you get this right,
everything else is easy. This position is determined more by how you
intend to use your bike than by anything else. If you look at a
typical bike, the saddle is behind the crank center, or bottom
bracket. There's a frame tube (the seat tube) running from the cranks
to the saddle, and it's at an angle. That angle partly determines the
fore-aft position of the saddle relative to the cranks and pedals.
That fore-aft position determines how your body is balanced on the
bicycle. Your balance determines how comfortable you are, and how
efficiently you can pedal the bike.

Stand up straight in front of a mirror and turn to the side. Look at
yourself in the mirror. When standing straight your head, hands, seat
and feet are all fairly close to being in line with each other. Now
bend over at the waist. Notice that not only has your head moved to a
position ahead of your feet, but your rear end has moved behind your
feet. If this were not the case, you would fall forward. Your seat
moves back when you bend at the waist to keep you in balance.

Your torso needs to be leaning forward for two reasons; power output
and aerodynamics. With an upright torso, you can't use the gluteus
muscles to good effect. Also, you can't effectively pull up on the
handlebar from an upright position. An upright torso is also very poor
aerodynamically. When cycling on level ground, the majority of your
effort goes against wind resistance. The easier it is for your body to
move through the air, the less work you'll have to do. With your torso
closer to horizontal, you present less frontal surface to the air and
don't have to work as hard to maintain a given speed.

Obviously, the most aerodynamically efficient position may not be the
most pleasant position to be in for several hours on a cross country
tour. So there's a tradeoff. As you move to a more horizontal
position, the saddle needs to be positioned further to the rear to
maintain your body's balance, just as your rear end moves to the rear
as you bend over while standing. It so happens that racers are more
inclined to use a horizontal torso position than tourers, and racers
are more concerned with having the handlebars further forward to make
climbing and sprinting out of the saddle more effective."

cheers Iain
  #5  
Old March 18th 04, 06:54 PM
Zog The Undeniable
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Default Longtitudinal saddle position

DavidR wrote:

I am trying to buy a replacement stem for a friend that has changed his
drops for butterflies and agonising over the correct size. It is on a Galaxy
which has a 110mm stem. The butterfly shape takes it +70 -100 mm from the
stem.

St John's Street has 150mm and 175mm stems. I am worried about getting a
150 in case it is still too short. My inclination is to go for the 175 and
move the saddle forward if it is too long .

My friend then showed me all the books that that say the saddle should be
set so that there is a plumb line between knee and pedal. Eh? All I have
ever done is move the saddle so that I sit on it properly.


This has more or less been shown to be balderdash. Basically move it
until the pedalling action feels right. If you're constantly pushing
your bum back to try and get a bit more power on the flat (you'll always
have to do this uphill), the seat needs to go back.

Then, and only then, go and buy the right length stem!
  #6  
Old March 18th 04, 09:14 PM
DavidR
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Default Longtitudinal saddle position


"Pete Biggs" wrote
DavidR wrote:
I am trying to buy a replacement stem for a friend that has changed
his drops for butterflies and agonising over the correct size. It is
on a Galaxy which has a 110mm stem. The butterfly shape takes it +70
-100 mm from the stem.

St John's Street has 150mm and 175mm stems. I am worried about
getting a 150 in case it is still too short.


I don't have experience of butterfly bars but I wouldn't expect such a
long stem to be required, necessarily, despite the bars having a negative
reach, as a more upright position is bound to be desired.
Stems longer
than 140mm are unusual on any kind of bike with any kind of bars. You
have to start worrying about flex and strength once you get beyond that.


A butterfly has over 800mm of pipe. I doubt stem flex would get much look
in!


My inclination is to go
for the 175 and move the saddle forward if it is too long .

My friend then showed me all the books that that say the saddle
should be set so that there is a plumb line between knee and pedal.


That's rubbish. Search the web for "The myth of KOPS", etc.


Before I read this I had exactly the same thoughts (that is, the rotation
around the BB being independant of gravity).

However, it
is important that the saddle should be set for comfortable seating and
pedalling (that's usually back a bit, whatever the stem is), not adjusted
to correct reach to the bars. That's what the top tube, stem and bars are
for.


The thing is that it is the saddle that is adjustable. You can have
the frame in any length as long as it is 560mm. Stems are expensive. If stem
length is changed it seems worth getting a big difference and making the
fine adjustment with the saddle. I see the 150 stem as leaving no room for
error (although the extra height will make up some of the difference). If
the 175 is too long, the saddle only needs to move by 20mm.

I haven't been talked out of the longer stem yet but I am still very
undecided.




  #7  
Old March 19th 04, 08:51 AM
Pete Biggs
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Default Longtitudinal saddle position

DavidR wrote:

The thing is that it is the saddle that is adjustable.


It is adjustable but you should adjust it only for the correct
reason........

You can have
the frame in any length as long as it is 560mm. Stems are expensive.


Decent quality stems can be bought for less than 15 and some money can be
recouped from any unsuitable ones by selling them on (might even find a
friendly bike shop that would lend some or try fitting various stems in
the shop). Alternatively, there are adjustable stems, which are indeed
expensive but at least provide lots of scope and therefore peace of mind.

If stem length is changed it seems worth getting a big difference and
making the fine adjustment with the saddle.


That would be a big mistake. Saddle longitudinal position has more
important effects than the reach to the bars. Even a small difference in
saddle position will affect saddle comfort and pedalling efficiency,
regardless of handlebar stem. It's about angle of legs to pedals and tilt
of pelvis, etc.

A 10mm difference in stem length is quite significant. You've got to be
very careful when making changes bigger than this, although I understand
the difficulty when changing to a different type of bars. There's similar
trouble when building a new bike with a different size/shape frame from
what one is used to. That's why I suggest considering an adjustable
stem - even if it would eventually be replaced with an ordinary one -
you'd at least be able to experiment and discover what extension and rise
works.

With a fixed stem though, when it comes to the final adjustment, careful
fine tuning of the height can make the bars feel comfortable for whatever
reach you have when reach is within 5 to 10mm of "correct". It's better
to do this than adjust the saddle, IMO.

I know it's all a lot of trouble (been there done that) but it's worth it
in the end.

I see the 150 stem as
leaving no room for error (although the extra height will make up
some of the difference). If the 175 is too long, the saddle only
needs to move by 20mm.


ONLY!!!! Even 2 to 5mm makes a difference to pedalling position, let
alone 20.

~PB


  #8  
Old March 19th 04, 09:16 AM
Richard Goodman
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Default Longtitudinal saddle position

"Pete Biggs" wrote in message
...
snip

I see the 150 stem as
leaving no room for error (although the extra height will make up
some of the difference). If the 175 is too long, the saddle only
needs to move by 20mm.


ONLY!!!! Even 2 to 5mm makes a difference to pedalling position, let
alone 20.


Well, Pete, all I can say is you must very much in tune with your
innerself - no, sorry, _outer_ self - I had a pair of butterfly bars and
played around with saddle position, stem length, bar angle etc - and
although some positions were more comfortable than others and I eventually
settled on a particular arrangement, I can't honestly say that I noticed a
difference of as little as 2 - 5mm in any setting as offering a significant
benefit in terms of comfort or pedalling ability. I have certainly not
noticed lateral adjustment of the saddle by those sort of distances making
any difference. In terms of the bars, I found whatever change meant a trade
off of one thing against another, getting the 'right' position was mainly
just a balancing act and highly subjective, and, at the margins, impossible
to say whether one setting was really better than another. In the end I
just gave up trying to find the optimal setting (and gave up with the bars
as well).

Rich


  #9  
Old March 19th 04, 10:34 AM
Just zis Guy, you know?
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Default Longtitudinal saddle position

On Thu, 18 Mar 2004 21:14:16 -0000, "DavidR"
wrote in message :

That's rubbish. Search the web for "The myth of KOPS", etc.


AASHTA: url:http://www.sheldonbrown.com/kops.html

--
Guy
===
May contain traces of irony. Contents liable to settle after posting.
http://www.chapmancentral.co.uk

88% of helmet statistics are made up, 65% of them at Washington University
  #10  
Old March 19th 04, 11:22 AM
Pete Biggs
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Default Longtitudinal saddle position

Richard Goodman wrote:

I see the 150 stem as
leaving no room for error (although the extra height will make up
some of the difference). If the 175 is too long, the saddle only
needs to move by 20mm.


ONLY!!!! Even 2 to 5mm makes a difference to pedalling position,
let alone 20.


Perhaps I should have inserted a "can" in there.

Well, Pete, all I can say is you must very much in tune with your
innerself - no, sorry, _outer_ self - I had a pair of butterfly
bars and played around with saddle position, stem length, bar angle
etc - and although some positions were more comfortable than others
and I eventually settled on a particular arrangement, I can't
honestly say that I noticed a difference of as little as 2 - 5mm in
any setting as offering a significant benefit in terms of comfort or
pedalling ability. I have certainly not noticed lateral adjustment
of the saddle by those sort of distances making any difference. In
terms of the bars, I found whatever change meant a trade off of one
thing against another, getting the 'right' position was mainly just a
balancing act and highly subjective, and, at the margins, impossible
to say whether one setting was really better than another. In the
end I just gave up trying to find the optimal setting (and gave up
with the bars as well).


I appreciate that different people are sensitive to different amounts of
variation (although the amounts can lessen as one becomes closer to the
ideal position*) but I think the principle is still good: set saddle so
it's right for pedalling then worry about reach to bars afterwards. In
the OP's case, the compensation required could end up even more than the
quoted 20mm (and I think 20mm is dodgy enough).

Personally, I was experimenting just the other day with a new saddle and
found 5mm adjustments made a significant difference to how comfortable my
outer self felt! And I've previously experimented with simultanous stem
and saddle settings: saddle forwards 10mm with stem longer by 10mm does
not feel the same as saddle and stem back by 10mm.

Another factor that we've forgotten to mention is steering and handling.
Things can get weird when the stem is extremely long: sluggish steering
and pedalling whilst standing may become awkward.

* If you're way out to start with, with any factor (saddle
height/reach/whatever), then yes 5 or even 10mm might not even be
noticeable at all, but when you've settled on what feels like an almost
perfect position and have become used to it, even a 2mm difference can
result in either an improvement or discomfort... in my experience anyway.

~PB


 




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