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rear der adjustment



 
 
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  #1  
Old March 15th 08, 08:27 PM posted to rec.bicycles.tech
Jim F
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Posts: 49
Default rear der adjustment

I changed out my rear wheel for my wife's, and now it won't shift to the
highest gear.

Both are Shimano nine-speed.
The derailer is c. 2000 Ultegra.
My wheel was a low-end Mavic rim with some whatever hub.
Hers is a Rolf Sestriere.
Low gears are fine, and shifting is otherwise okay.

I tried the H limit screw on the derailer.
The derailer hanger seems aligned fine.
I reviewed Sheldon's page.

Any suggestions?

--
JF

"Here comes the lightening and here comes the thunder. Ride on the storm and
take it to the sea. "
- Jim Hunter



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  #2  
Old March 15th 08, 09:03 PM posted to rec.bicycles.tech
Ben C
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Posts: 3,084
Default rear der adjustment

On 2008-03-15, Jim F wrote:
I changed out my rear wheel for my wife's, and now it won't shift to the
highest gear.

Both are Shimano nine-speed.
The derailer is c. 2000 Ultegra.
My wheel was a low-end Mavic rim with some whatever hub.
Hers is a Rolf Sestriere.
Low gears are fine, and shifting is otherwise okay.

I tried the H limit screw on the derailer.
The derailer hanger seems aligned fine.
I reviewed Sheldon's page.

Any suggestions?


If the limit screw isn't what's limiting it then the cable may be too
tight.
  #3  
Old March 15th 08, 09:48 PM posted to rec.bicycles.tech
A Muzi
external usenet poster
 
Posts: 4,551
Default rear der adjustment

Jim F wrote:
I changed out my rear wheel for my wife's, and now it won't shift to the
highest gear.
Both are Shimano nine-speed.
The derailer is c. 2000 Ultegra.
My wheel was a low-end Mavic rim with some whatever hub.
Hers is a Rolf Sestriere.
Low gears are fine, and shifting is otherwise okay.
I tried the H limit screw on the derailer.
The derailer hanger seems aligned fine.
I reviewed Sheldon's page.
Any suggestions?


Check that it's aligned, set the limit screws and double check by
shifting smartly with your left thumb before connecting the gear wire.
--
Andrew Muzi
www.yellowjersey.org
Open every day since 1 April, 1971
  #4  
Old March 15th 08, 10:29 PM posted to rec.bicycles.tech
Jim F
external usenet poster
 
Posts: 49
Default rear der adjustment

"Ben C" wrote...

If the limit screw isn't what's limiting it then the cable may be too
tight.


Bingo. That, plus I opened it up half a turn.

Thanks,

--
JF

"Here comes the lightening and here comes the thunder. Ride on the storm and
take it to the sea. "
- Jim Hunter



  #5  
Old March 16th 08, 10:45 AM posted to rec.bicycles.tech
Dave
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Posts: 3
Default rear der adjustment

On Mar 15, 5:29 pm, "Jim F" wrote:
"Ben C" wrote...

If the limit screw isn't what's limiting it then the cable may be too
tight.


Bingo. That, plus I opened it up half a turn.

Thanks,

--
JF

"Here comes the lightening and here comes the thunder. Ride on the storm and
take it to the sea. "
- Jim Hunter


The only thing the high and low limit screws do is limit how far a
derailleur can move in either direction. That adjustment can be made
without a cable being attached. After that how well the indexing works
is determined by cable tension.

There are videos on Utube that explain the concept very well.
  #6  
Old March 16th 08, 12:32 PM posted to rec.bicycles.tech
Lou Holtman
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Posts: 627
Default rear der adjustment

Dave wrote:
On Mar 15, 5:29 pm, "Jim F" wrote:
"Ben C" wrote...

If the limit screw isn't what's limiting it then the cable may be too
tight.

Bingo. That, plus I opened it up half a turn.

Thanks,

--
JF

"Here comes the lightening and here comes the thunder. Ride on the storm and
take it to the sea. "
- Jim Hunter


The only thing the high and low limit screws do is limit how far a
derailleur can move in either direction. That adjustment can be made
without a cable being attached. After that how well the indexing works
is determined by cable tension.


I find that a very confusing description 'adjusting cable tension'. The
tension is determined by de spring in the derailleur. You adjust the
POSITION of the upper pulley with barrel adjuster.

Lou
  #7  
Old March 16th 08, 12:42 PM posted to rec.bicycles.tech
Ben C
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Posts: 3,084
Default rear der adjustment

On 2008-03-16, Lou Holtman wrote:
Dave wrote:
On Mar 15, 5:29 pm, "Jim F" wrote:
"Ben C" wrote...

If the limit screw isn't what's limiting it then the cable may be too
tight.
Bingo. That, plus I opened it up half a turn.

Thanks,

--
JF

"Here comes the lightening and here comes the thunder. Ride on the storm and
take it to the sea. "
- Jim Hunter


The only thing the high and low limit screws do is limit how far a
derailleur can move in either direction. That adjustment can be made
without a cable being attached. After that how well the indexing works
is determined by cable tension.


I find that a very confusing description 'adjusting cable tension'. The
tension is determined by de spring in the derailleur. You adjust the
POSITION of the upper pulley with barrel adjuster.


If the derailleur is on its lower limit screw and you turn the barrel
you will be increasing tension in the cable.
  #8  
Old March 16th 08, 01:19 PM posted to rec.bicycles.tech
Lou Holtman
external usenet poster
 
Posts: 627
Default rear der adjustment

Ben C wrote:
On 2008-03-16, Lou Holtman wrote:
Dave wrote:
On Mar 15, 5:29 pm, "Jim F" wrote:
"Ben C" wrote...

If the limit screw isn't what's limiting it then the cable may be too
tight.
Bingo. That, plus I opened it up half a turn.

Thanks,

--
JF

"Here comes the lightening and here comes the thunder. Ride on the storm and
take it to the sea. "
- Jim Hunter
The only thing the high and low limit screws do is limit how far a
derailleur can move in either direction. That adjustment can be made
without a cable being attached. After that how well the indexing works
is determined by cable tension.

I find that a very confusing description 'adjusting cable tension'. The
tension is determined by de spring in the derailleur. You adjust the
POSITION of the upper pulley with barrel adjuster.


If the derailleur is on its lower limit screw and you turn the barrel
you will be increasing tension in the cable.



Yeah by 0.001% or something. The main purpose is POSITIONING the upper
pulley, by in- or decreasing the length of the outer cable between two
cable stops. The tiny weeny in- or decrease of the tension, which you
can not feel in the cable, is a side effect. Why not call by the right
name instead of that voodoo bicycle tech talk nobody 'not in the
business' understands. It's like calling shifting to another gear in- or
decreasing cable tension.


Lou
  #9  
Old March 16th 08, 01:42 PM posted to rec.bicycles.tech
Ben C
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Posts: 3,084
Default rear der adjustment

On 2008-03-16, Lou Holtman wrote:
Ben C wrote:
On 2008-03-16, Lou Holtman wrote:

[...]
I find that a very confusing description 'adjusting cable tension'. The
tension is determined by de spring in the derailleur. You adjust the
POSITION of the upper pulley with barrel adjuster.


If the derailleur is on its lower limit screw and you turn the barrel
you will be increasing tension in the cable.


Yeah by 0.001% or something. The main purpose is POSITIONING the upper
pulley, by in- or decreasing the length of the outer cable between two
cable stops.


Why the outer cable?

The way I assume it works is like this: the shifter is clicked into the
position for third gear (for example). You set the (inner) cable length
to just the right length to position the derailleur nicely on third
gear.

You should now hit the other gears correctly as the shifter changes the
cable length by the right amount for the distance between gears.

The tiny weeny in- or decrease of the tension, which you
can not feel in the cable, is a side effect. Why not call by the right
name instead of that voodoo bicycle tech talk nobody 'not in the
business' understands.


Anyway if you did rack up the tension with the derailleur on the lower
limit screw you wouldn't achieve anything useful.

It's like calling shifting to another gear in- or
decreasing cable tension.


Which it isn't. As you say it's the cable length you're setting here and
the tension is always the same and determined by the derailleur spring.
  #10  
Old March 16th 08, 02:11 PM posted to rec.bicycles.tech
Barry
external usenet poster
 
Posts: 40
Default rear der adjustment

tension is determined by de spring in the derailleur. You adjust the
POSITION of the upper pulley with barrel adjuster.


If the derailleur is on its lower limit screw and you turn the barrel
you will be increasing tension in the cable.


Yeah by 0.001% or something. The main purpose is POSITIONING the upper
pulley, by in- or decreasing the length of the outer cable between two cable
stops. The tiny weeny in- or decrease of the tension, which you can not feel
in the cable, is a side effect.


Here's how I would describe the physics. You apply a torque to turn the
barrel, which transmits a force to the cable and pulls it a little harder -
this pull is the cable tension. The other end of the cable transmits this
pull to the derailleur. As the derailleur moves, its spring lengthens, and
the spring force increases to balance the increased cable tension.

Look at it this way. If the derailleur spring was replaced by something like
a solid rod, the derailleur would hardly move, and cable tension would have to
be increased a lot for a tiny bit of movement. On the other hand, if the
spring was very weak, a small increase in cable tension would cause a large
movement. If you find it clearer to refer to cable length instead of tension,
that's fine. But I think it's wrong to call the tension increase a "side
effect," as it's the increase in tension that causes everything else to
happen.

Barry


 




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