Mathematician required

Pete Biggs p@honeydewbiggs{remove_melon}.tc said:

Many fanx!

Fanx? What's that?

Remind me how head tube angle is measured. Stem angle is angle from the
vertical?

Arthur

--
Arthur Clune PGP/GPG Key: http://www.clune.org/pubkey.txt
The struggle of people against power is the struggle
of memory against forgetting - Milan Kundera

I said:

Assuming a 73 degree head angle, how much reach would be lost if I
lowered a 73 degree stem to get the same handlebar height as I did
from a 76 degree stem with the same extension?

ps. This is with the stems pointing upwards, ie. +17 deg and +14 deg,

Pete Biggs said:

Assuming a 73 degree head angle, how much reach would be lost if I lowered
a 73 degree stem to get the same handlebar height as I did from a 76
degree stem with the same extension?

I'm not all sure I understand what you mean, but I reckon that a 73deg
stem will have to be raised to give the same height, and the reach will
decrease by 1.5% of the length of the extension.

Mike

Mike Causer said:

Quoted message said:

Assuming a 73 degree head angle, how much reach would be lost if I
lowered a 73 degree stem to get the same handlebar height as I did
from a 76 degree stem with the same extension?

I'm not all sure I understand what you mean,

I'm wodering what the effect on reach would be if I replaced a 76deg stem
with a 73deg stem, setting the new stem up so handlebar height would be
same as before.

I should have included: Extension of both stems is 90mm.

Quoted message said:

but I reckon that a 73deg
stem will have to be raised to give the same height, and the reach
will decrease by 1.5% of the length of the extension.

Thanks Mike. So that'll be 1.35mm in my case? (Not as much as I feared).

~PB

Arthur Clune said:

Pete Biggs p@honeydewbiggs{remove_melon}.tc said:

Many fanx!

Fanx? What's that?

Norf London (or text) for "thanks". :-)

Quoted message said:

Remind me how head tube angle is measured. Stem angle is angle from
the vertical?

I better leave that to someone else to explain, if they would be so kind.
Frankly, I'm not too good with angles, hence my question.

~PB

Pete Biggs said:

Mike Causer said:

Quoted message said:

Assuming a 73 degree head angle, how much reach would be lost if I
lowered a 73 degree stem to get the same handlebar height as I did
from a 76 degree stem with the same extension?

Ooh loads. (a.k.a. no 'kin idea.)

Sorry geez. (East London 'mate'😉 :-)

--
Mark
_____________________________________________

Deja Moo - The feeling that you've heard this bull before

"Pete Biggs" <p@honeydewbiggs{remove_melon}.tc> wrote in message
news:[email hidden]...

Quoted message said:

Assuming a 73 degree head angle, how much reach would be lost if I lowered
a 73 degree stem to get the same handlebar height as I did from a 76
degree stem with the same extension?

Many fanx!

Assuming i understand your question; AND -

Assuming that the extension is 90 mm in length, and that this is installed
in a stem at 73deg, ie 17 deg from vertical, the handlebar centre point will
be
90 x cos17
= 90 x 0.9563
= 86.06 mm above the stem centre line

and 90 * sin17
= 90 * 0.2924
=26.3 mm behind the stem centre line

Assuming that you then want the same handle bar height at a stem angle of 76
deg - ie 14 deg from vertical - then the handlebar centre point will be
86.06 * tan14
=86.06 * 0.2493
=21.46 mm behind the centre line

You will have to reach (26.3 - 21.46) = 4.84 mm further forward.

You could move your saddle forward a bit, but I'm apprehensive that this
would lead to a supplementary question about the angle of your leg pushing
the pedals down .....

Numbers are rounded.

Once again, a bus driver comes to the aid of the freeloaders. Can't you use
Excel????

:o)

--
IanH

In article <[email hidden]>, ian henden

Quoted message said:

Once again, a bus driver comes to the aid of the freeloaders.
Can't you use Excel????

It's actually easier to get some thin bits of wood and a few panel
pins - you can then physically see what you might end up with - and
you have room for improvement/change.

--
A T (Sandy) Morton
on the Bicycle Island
In the Global Village
http://www.millport.net

ian henden said:

You will have to reach (26.3 - 21.46) = 4.84 mm further forward.

You could move your saddle forward a bit, but I'm apprehensive that this
would lead to a supplementary question about the angle of your leg pushing
the pedals down .....

Numbers are rounded.

Once again, a bus driver comes to the aid of the freeloaders. Can't you use
Excel????

You make a minor error and end up with the wrong answer.

What we do not know is the angle of the head tube. Typically on a road
bike the stem will have an angle of about 72-78 degrees which is about
the same angle the head tube makes. This leaves the stem extension
horizontal. Any change in angle from horizontal with the same nominal
extension will result in a shortening of the distance one has to reach.

So the critical question is: what is the angle of the head tube? then a
correct answer can be determined.

...d

David Martin said:

What we do not know is the angle of the head tube. Typically on a road
bike the stem will have an angle of about 72-78 degrees which is about
the same angle the head tube makes. This leaves the stem extension
horizontal. Any change in angle from horizontal with the same nominal
extension will result in a shortening of the distance one has to
reach.

So the critical question is: what is the angle of the head tube? then
a correct answer can be determined.

I stated head angle in my first post: 73 degrees.

~PB

ian henden said:

Quoted message said:

Assuming a 73 degree head angle, how much reach would be lost if I
lowered a 73 degree stem to get the same handlebar height as I did
from a 76 degree stem with the same extension?

Many fanx!

Assuming i understand your question; AND -

Assuming that the extension is 90 mm in length, and that this is
installed in a stem at 73deg, ie 17 deg from vertical, the handlebar
centre point will be
90 x cos17
= 90 x 0.9563
= 86.06 mm above the stem centre line

and 90 * sin17
= 90 * 0.2924
=26.3 mm behind the stem centre line

Assuming that you then want the same handle bar height at a stem
angle of 76 deg - ie 14 deg from vertical - then the handlebar centre
point will be
86.06 * tan14
=86.06 * 0.2493
=21.46 mm behind the centre line

You will have to reach (26.3 - 21.46) = 4.84 mm further forward.

Thank you Ian. Actually, it's the other way round: I'm considering
replacing a 76 degree stem with a better stem that happens to be 73 deg,
so I'll stick a minus sign in front of your answer.

Quoted message said:

You could move your saddle forward a bit, but I'm apprehensive that
this would lead to a supplementary question about the angle of your
leg pushing the pedals down .....

:-)

~PB

David Martin said:

Typically on a road
bike the stem will have an angle of about 72-78 degrees which is about
the same angle the head tube makes. This leaves the stem extension
horizontal.

I'm not using a typical road bike stem angle. The extension isn't
anything like horizontal, it rises quite steeply. I'm considering using
107 degrees (upside down 73) on a bike with a 73 head angle, instead of
104 degrees.

Sorry if I didn't make it clear enough in the first place. But if it was
all crystal clear to me I wouldn't have to ask the question! :-)

By the way, 80 and 82 degree stems are pretty common on road bikes as well
nowadays with A-Head stems.

~PB

"Pete Biggs" <p@honeydewbiggs{remove_melon}.tc> wrote in message
news:[email hidden]...

Quoted message said:

ian henden said:

Quoted message said:

Assuming a 73 degree head angle, how much reach would be lost if I
lowered a 73 degree stem to get the same handlebar height as I did
from a 76 degree stem with the same extension?

Many fanx!

Assuming i understand your question; AND -

Assuming that the extension is 90 mm in length, and that this is
installed in a stem at 73deg, ie 17 deg from vertical, the handlebar
centre point will be
90 x cos17
= 90 x 0.9563
= 86.06 mm above the stem centre line

and 90 * sin17
= 90 * 0.2924
=26.3 mm behind the stem centre line

Assuming that you then want the same handle bar height at a stem
angle of 76 deg - ie 14 deg from vertical - then the handlebar centre
point will be
86.06 * tan14
=86.06 * 0.2493
=21.46 mm behind the centre line

You will have to reach (26.3 - 21.46) = 4.84 mm further forward.

Thank you Ian. Actually, it's the other way round: I'm considering
replacing a 76 degree stem with a better stem that happens to be 73 deg,
so I'll stick a minus sign in front of your answer.

It would be mathematically incorrect to do so, but you are unlikely to be
far out - who is going to argue about a millimeter? I miss cyclists by
less than that, with my bus!!!!!

(only joking!!!)

IanH

in message <[email hidden]>, David

Martin (') said:

ian henden said:

You will have to reach (26.3 - 21.46) = 4.84 mm further forward.

You could move your saddle forward a bit, but I'm apprehensive that
this would lead to a supplementary question about the angle of your
leg pushing the pedals down .....

Numbers are rounded.

Once again, a bus driver comes to the aid of the freeloaders. Can't
you use Excel????

You make a minor error and end up with the wrong answer.

What we do not know is the angle of the head tube. Typically on a road
bike the stem will have an angle of about 72-78 degrees which is about
the same angle the head tube makes. This leaves the stem extension
horizontal. Any change in angle from horizontal with the same nominal
extension will result in a shortening of the distance one has to
reach.

But even that doesn't address the situation since the position of the
shoulder and elbow joints isn't horizontally behind the handlebar, but
at a position behind and above it which is sensitive to movements of
both the handlebar and of the saddle. So the really precise
mathematical answer is suck it and see.

--
[email hidden] (Simon Brooke) http://www.jasmine.org.uk/~simon/

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