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Shifting problems on Stronglight 86mm BCD cranks



 
 
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  #1  
Old July 6th 04, 03:02 PM
David Damerell
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Default Shifting problems on Stronglight 86mm BCD cranks

I recently acquired an '89 Super Galaxy tandem. This has Stronglight
cranks on, with a single 86mm BCD for a triple. The bicycle's original
gearing was 48/42/28 chainrings with a 13-28 six speed rear freewheel.

Of course, tandems being pretty quick, we found ourselves spinning out the
48/13 almost immediately. Hence I ordered a 52t 86mm chainring and fitted
it.

However, the chain falls down the gap between the 52t and 42t chainrings,
which is a nuisance. Furthermore, I intended to replace the rear hub with
a 7-speed cassette hub; we plan to do the End to End on this tandem and I
don't expect to be able to find 6s freewheels in the back of beyond, I
have a bunch of existing 7s gear, and an 11t top sprocket would also
alleviate the gear range problems. However, I'm concerned that a narrower
chain will only exacerbate this problem.

I'm not sure what the answer is. "New cranks" is obvious, but expensive.
Returning to 48/42/28 might sort it out, but then the gearing's less
useful. Another idea that springs to mind is drilling into the 52 and 42
just below the teeth on the 42, and bolting them together - both to make
them slightly closer, and to make it impossible for the chain to descend
below that level. Grinding down the flats that engage with the spider
would also decrease the spacing, but seems pretty drastic.

I'd be grateful for any advice people can offer.
--
David Damerell Kill the tomato!
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  #2  
Old July 6th 04, 06:07 PM
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Posts: n/a
Default Shifting problems on Stronglight 86mm BCD cranks

On 06 Jul 2004 15:02:24 +0100 (BST), David Damerell
wrote:

I recently acquired an '89 Super Galaxy tandem. This has Stronglight
cranks on, with a single 86mm BCD for a triple. The bicycle's original
gearing was 48/42/28 chainrings with a 13-28 six speed rear freewheel.

Of course, tandems being pretty quick, we found ourselves spinning out the
48/13 almost immediately. Hence I ordered a 52t 86mm chainring and fitted
it.

However, the chain falls down the gap between the 52t and 42t chainrings,
which is a nuisance. Furthermore, I intended to replace the rear hub with
a 7-speed cassette hub; we plan to do the End to End on this tandem and I
don't expect to be able to find 6s freewheels in the back of beyond, I
have a bunch of existing 7s gear, and an 11t top sprocket would also
alleviate the gear range problems. However, I'm concerned that a narrower
chain will only exacerbate this problem.

I'm not sure what the answer is. "New cranks" is obvious, but expensive.
Returning to 48/42/28 might sort it out, but then the gearing's less
useful. Another idea that springs to mind is drilling into the 52 and 42
just below the teeth on the 42, and bolting them together - both to make
them slightly closer, and to make it impossible for the chain to descend
below that level. Grinding down the flats that engage with the spider
would also decrease the spacing, but seems pretty drastic.

I'd be grateful for any advice people can offer.


Dear David,

Could you be using an unusually thin chain?

Last August, Pete Biggs asked about fatter chains for 5 and
6 speed bikes, and Dianne_1234 shamelessly published widths
from 6.60mm to 8.61mm:

http://groups.google.com/groups?hl=e...om%26rnum%3D29

or

http://tinyurl.com/27po5

Carl Fogel
  #3  
Old July 6th 04, 06:07 PM
external usenet poster
 
Posts: n/a
Default Shifting problems on Stronglight 86mm BCD cranks

On 06 Jul 2004 15:02:24 +0100 (BST), David Damerell
wrote:

I recently acquired an '89 Super Galaxy tandem. This has Stronglight
cranks on, with a single 86mm BCD for a triple. The bicycle's original
gearing was 48/42/28 chainrings with a 13-28 six speed rear freewheel.

Of course, tandems being pretty quick, we found ourselves spinning out the
48/13 almost immediately. Hence I ordered a 52t 86mm chainring and fitted
it.

However, the chain falls down the gap between the 52t and 42t chainrings,
which is a nuisance. Furthermore, I intended to replace the rear hub with
a 7-speed cassette hub; we plan to do the End to End on this tandem and I
don't expect to be able to find 6s freewheels in the back of beyond, I
have a bunch of existing 7s gear, and an 11t top sprocket would also
alleviate the gear range problems. However, I'm concerned that a narrower
chain will only exacerbate this problem.

I'm not sure what the answer is. "New cranks" is obvious, but expensive.
Returning to 48/42/28 might sort it out, but then the gearing's less
useful. Another idea that springs to mind is drilling into the 52 and 42
just below the teeth on the 42, and bolting them together - both to make
them slightly closer, and to make it impossible for the chain to descend
below that level. Grinding down the flats that engage with the spider
would also decrease the spacing, but seems pretty drastic.

I'd be grateful for any advice people can offer.


Dear David,

Could you be using an unusually thin chain?

Last August, Pete Biggs asked about fatter chains for 5 and
6 speed bikes, and Dianne_1234 shamelessly published widths
from 6.60mm to 8.61mm:

http://groups.google.com/groups?hl=e...om%26rnum%3D29

or

http://tinyurl.com/27po5

Carl Fogel
  #4  
Old July 6th 04, 10:32 PM
Benjamin Weiner
external usenet poster
 
Posts: n/a
Default Shifting problems on Stronglight 86mm BCD cranks

David Damerell wrote:

However, the chain falls down the gap between the 52t and 42t chainrings,
which is a nuisance. Furthermore, I intended to replace the rear hub with
a 7-speed cassette hub; we plan to do the End to End on this tandem and I
don't expect to be able to find 6s freewheels in the back of beyond, I
have a bunch of existing 7s gear, and an 11t top sprocket would also
alleviate the gear range problems. However, I'm concerned that a narrower
chain will only exacerbate this problem.


I'm not sure what the answer is. "New cranks" is obvious, but expensive.
Returning to 48/42/28 might sort it out, but then the gearing's less
useful. Another idea that springs to mind is drilling into the 52 and 42
just below the teeth on the 42, and bolting them together - both to make
them slightly closer, and to make it impossible for the chain to descend
below that level. Grinding down the flats that engage with the spider
would also decrease the spacing, but seems pretty drastic.


The crankset may have been designed with wider, 5/6 speed chain
in mind, where the rivets stick out more. Many chainrings are
asymmetric - perhaps the 42 can be turned around, However, there
is a better solution.

I "pinned" a 52 in an attempt to mimic the Shimano pins that
assist 42-52 upshifts. I tapped small holes in the chainring a bit
below the teeth, and inserted short M5 setscrews that poke inside
by 1-2mm, just enough so the chain doesn't hit them when it's on
the 42. If you do this I think the setscrews will push the chain
inside enough to land on the 42 when downshifting.

I used a tapered tap and didn't run it quite all the way through,
so the screws are a tight fit. This keeps them from vibrating out.

  #5  
Old July 6th 04, 10:32 PM
Benjamin Weiner
external usenet poster
 
Posts: n/a
Default Shifting problems on Stronglight 86mm BCD cranks

David Damerell wrote:

However, the chain falls down the gap between the 52t and 42t chainrings,
which is a nuisance. Furthermore, I intended to replace the rear hub with
a 7-speed cassette hub; we plan to do the End to End on this tandem and I
don't expect to be able to find 6s freewheels in the back of beyond, I
have a bunch of existing 7s gear, and an 11t top sprocket would also
alleviate the gear range problems. However, I'm concerned that a narrower
chain will only exacerbate this problem.


I'm not sure what the answer is. "New cranks" is obvious, but expensive.
Returning to 48/42/28 might sort it out, but then the gearing's less
useful. Another idea that springs to mind is drilling into the 52 and 42
just below the teeth on the 42, and bolting them together - both to make
them slightly closer, and to make it impossible for the chain to descend
below that level. Grinding down the flats that engage with the spider
would also decrease the spacing, but seems pretty drastic.


The crankset may have been designed with wider, 5/6 speed chain
in mind, where the rivets stick out more. Many chainrings are
asymmetric - perhaps the 42 can be turned around, However, there
is a better solution.

I "pinned" a 52 in an attempt to mimic the Shimano pins that
assist 42-52 upshifts. I tapped small holes in the chainring a bit
below the teeth, and inserted short M5 setscrews that poke inside
by 1-2mm, just enough so the chain doesn't hit them when it's on
the 42. If you do this I think the setscrews will push the chain
inside enough to land on the 42 when downshifting.

I used a tapered tap and didn't run it quite all the way through,
so the screws are a tight fit. This keeps them from vibrating out.

  #6  
Old July 7th 04, 10:46 AM
David Damerell
external usenet poster
 
Posts: n/a
Default Shifting problems on Stronglight 86mm BCD cranks

Benjamin Weiner wrote:
David Damerell wrote:
However, the chain falls down the gap between the 52t and 42t chainrings,
which is a nuisance.

The crankset may have been designed with wider, 5/6 speed chain
in mind, where the rivets stick out more. Many chainrings are
asymmetric - perhaps the 42 can be turned around


Curiously, I noticed this after posting; for now I've flipped the 42.

I "pinned" a 52 in an attempt to mimic the Shimano pins that
assist 42-52 upshifts. I tapped small holes in the chainring a bit
below the teeth, and inserted short M5 setscrews that poke inside
by 1-2mm, just enough so the chain doesn't hit them when it's on
the 42. If you do this I think the setscrews will push the chain
inside enough to land on the 42 when downshifting.


Ingenious - but do they help with upshifts? The derailleur cage doesn't
provide much upwards hoik, because it has to do most of its work for the
28-42 shifts.
--
David Damerell Kill the tomato!
  #7  
Old July 7th 04, 10:46 AM
David Damerell
external usenet poster
 
Posts: n/a
Default Shifting problems on Stronglight 86mm BCD cranks

Benjamin Weiner wrote:
David Damerell wrote:
However, the chain falls down the gap between the 52t and 42t chainrings,
which is a nuisance.

The crankset may have been designed with wider, 5/6 speed chain
in mind, where the rivets stick out more. Many chainrings are
asymmetric - perhaps the 42 can be turned around


Curiously, I noticed this after posting; for now I've flipped the 42.

I "pinned" a 52 in an attempt to mimic the Shimano pins that
assist 42-52 upshifts. I tapped small holes in the chainring a bit
below the teeth, and inserted short M5 setscrews that poke inside
by 1-2mm, just enough so the chain doesn't hit them when it's on
the 42. If you do this I think the setscrews will push the chain
inside enough to land on the 42 when downshifting.


Ingenious - but do they help with upshifts? The derailleur cage doesn't
provide much upwards hoik, because it has to do most of its work for the
28-42 shifts.
--
David Damerell Kill the tomato!
  #8  
Old July 8th 04, 09:27 AM
Benjamin Weiner
external usenet poster
 
Posts: n/a
Default Shifting problems on Stronglight 86mm BCD cranks

David Damerell wrote:
Benjamin Weiner wrote:


I "pinned" a 52 in an attempt to mimic the Shimano pins that
assist 42-52 upshifts. I tapped small holes in the chainring a bit
below the teeth, and inserted short M5 setscrews that poke inside
by 1-2mm, just enough so the chain doesn't hit them when it's on
the 42. If you do this I think the setscrews will push the chain
inside enough to land on the 42 when downshifting.


Ingenious - but do they help with upshifts? The derailleur cage doesn't
provide much upwards hoik, because it has to do most of its work for the
28-42 shifts.


Yes, slightly. This is on a 52-42-30 with plain rings and an old
RSX STI triple front lever with no trim adjustment. If it was a
friction front shifter, the plain rings would work ok. With the
STI, there is a limited range of adjustment where upshifts work,
the der can push the chain down to the granny, and chain rub is
tolerable. The pins improve front upshifting enough to widen
this workable range. Late model Shimano rings also have some
shorter teeth to help the downshifting - I've been tempted to file
down a couple of teeth to imitate that.

Front STI is hardly ideal, but front shifting can be clumsy
even with a friction shifter, especially under load. I know,
it's "better" not to shift the front under load but if you have
hills it's sometimes unavoidable. The mutated chainrings seem
to help with that.

WRT the derailleur cage and upshifts, sometimes rotating the
FD about the seattube slightly helps with that. Triple fronts
can be a battle between quicker shifting and tolerable
chain rub. I'd like to see the manufacturers improve front
shifting before adding more rear cogs, but given the degrees
of freedom in any crankset/FD combination, that may be quite
hard.


  #9  
Old July 8th 04, 09:27 AM
Benjamin Weiner
external usenet poster
 
Posts: n/a
Default Shifting problems on Stronglight 86mm BCD cranks

David Damerell wrote:
Benjamin Weiner wrote:


I "pinned" a 52 in an attempt to mimic the Shimano pins that
assist 42-52 upshifts. I tapped small holes in the chainring a bit
below the teeth, and inserted short M5 setscrews that poke inside
by 1-2mm, just enough so the chain doesn't hit them when it's on
the 42. If you do this I think the setscrews will push the chain
inside enough to land on the 42 when downshifting.


Ingenious - but do they help with upshifts? The derailleur cage doesn't
provide much upwards hoik, because it has to do most of its work for the
28-42 shifts.


Yes, slightly. This is on a 52-42-30 with plain rings and an old
RSX STI triple front lever with no trim adjustment. If it was a
friction front shifter, the plain rings would work ok. With the
STI, there is a limited range of adjustment where upshifts work,
the der can push the chain down to the granny, and chain rub is
tolerable. The pins improve front upshifting enough to widen
this workable range. Late model Shimano rings also have some
shorter teeth to help the downshifting - I've been tempted to file
down a couple of teeth to imitate that.

Front STI is hardly ideal, but front shifting can be clumsy
even with a friction shifter, especially under load. I know,
it's "better" not to shift the front under load but if you have
hills it's sometimes unavoidable. The mutated chainrings seem
to help with that.

WRT the derailleur cage and upshifts, sometimes rotating the
FD about the seattube slightly helps with that. Triple fronts
can be a battle between quicker shifting and tolerable
chain rub. I'd like to see the manufacturers improve front
shifting before adding more rear cogs, but given the degrees
of freedom in any crankset/FD combination, that may be quite
hard.


  #10  
Old July 8th 04, 01:17 PM
David Damerell
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Posts: n/a
Default Shifting problems on Stronglight 86mm BCD cranks

Benjamin Weiner wrote:
[discussion of shifting problems on 52/42/28 Stronglight cranks]
WRT the derailleur cage and upshifts, sometimes rotating the
FD about the seattube slightly helps with that. Triple fronts
can be a battle between quicker shifting and tolerable
chain rub.


That (rotation) might be an idea. Chain rub is not so great an issue,
because the chainstays are quite long, presumably in order to bash the
stoker about a bit less over the bumps.
--
David Damerell Distortion Field!
 




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