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Cross shiftting



 
 
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  #1  
Old July 16th 11, 01:30 PM posted to rec.bicycles.tech
John B. slocomb
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Posts: 23
Default Cross shiftting


"Cross shifting", i.e., Large chain Ring/large cassette cog or small
chain ring/small cog is generally taken as a mortal sin. But with a
triple chain ring what limits are made to the shift pattern when on
the center ring? Assuming that the chain line through the center line
of the 5th cog, on a 9 speed cassette, and the center line of the
center chain ring?

It appears to me that considering the actual distance between the
three chain rings versus the actual distances on the cassette that the
center chain ring should be able to shift to any cog without problems.


John B. Slocomb
(johnbslocombatgmaildotcom)
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  #2  
Old July 16th 11, 04:38 PM posted to rec.bicycles.tech
Dan O
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Posts: 6,098
Default Cross shiftting

On Jul 16, 5:30 am, John B. Slocomb wrote:
"Cross shifting", i.e., Large chain Ring/large cassette cog or small
chain ring/small cog is generally taken as a mortal sin. But with a
triple chain ring what limits are made to the shift pattern when on
the center ring? Assuming that the chain line through the center line
of the 5th cog, on a 9 speed cassette, and the center line of the
center chain ring?

It appears to me that considering the actual distance between the
three chain rings versus the actual distances on the cassette that the
center chain ring should be able to shift to any cog without problems.


A good setup should allow shifting to any combination without
problems, but for riding along you ideally want a straight chain line,
so as you shift more toward one end or the other of the cassette for
more than some brief circumstances, consider finding a combination
that moves the chain laterally at the front and rear together, rather
than shifting way back and forth at one end. (too long sentence)


  #3  
Old July 16th 11, 05:12 PM posted to rec.bicycles.tech
Dan O
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Posts: 6,098
Default Cross shiftting

On Jul 16, 8:38 am, Dan O wrote:
On Jul 16, 5:30 am, John B. Slocomb wrote:

"Cross shifting", i.e., Large chain Ring/large cassette cog or small
chain ring/small cog is generally taken as a mortal sin. But with a
triple chain ring what limits are made to the shift pattern when on
the center ring? Assuming that the chain line through the center line
of the 5th cog, on a 9 speed cassette, and the center line of the
center chain ring?


It appears to me that considering the actual distance between the
three chain rings versus the actual distances on the cassette that the
center chain ring should be able to shift to any cog without problems.


A good setup should allow shifting to any combination without
problems, but for riding along you ideally want a straight chain line,
so as you shift more toward one end or the other of the cassette for
more than some brief circumstances, consider finding a combination
that moves the chain laterally at the front and rear together, rather
than shifting way back and forth at one end. (too long sentence)


For me this amounts to two modes of operation: Outer chainring with a
few, closely spaced outer cogs for most riding, and middle chainring
with a few middle-to-inner cogs for gnarly steep climbing. (The inner
ring is for some as yet unimagined scenario, like hauling heavy loads
out from the bottom of the Grand Canyon. The inner cog is reserved as
bail-out gear and pie-plate.)

On my liesure (whjeelie) bike, the two modes are middle ring with a
couple of middle-ish cogs for riding around town, and outer ring with
a couple of outer cogs for top speed to the fire station.
  #4  
Old July 16th 11, 06:15 PM posted to rec.bicycles.tech
Lou Holtman[_5_]
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Posts: 826
Default Cross shiftting

On 16 jul, 14:30, John B. Slocomb wrote:
"Cross shifting", i.e., Large chain Ring/large cassette cog or small
chain ring/small cog is generally taken as a mortal sin. But with a
triple chain ring what limits are made to the shift pattern when on
the center ring? Assuming that the chain line through the center line
of the 5th cog, on a 9 speed cassette, and the center line of the
center chain ring?

It appears to me that considering the actual distance between the
three chain rings versus the actual distances on the cassette that the
center chain ring should be able to shift to any cog without problems.

John B. Slocomb
(johnbslocombatgmaildotcom)


Middle ring should shift any cogs. Large chainring avoid two largest
cogs; small chainring avoid two smallest cogs. It is that simple.

Lou
  #5  
Old July 16th 11, 06:53 PM posted to rec.bicycles.tech
thirty-six
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Posts: 10,049
Default Cross shiftting

On Jul 16, 1:30*pm, John B. Slocomb wrote:
"Cross shifting", i.e., Large chain Ring/large cassette cog or small
chain ring/small cog is generally taken as a mortal sin. But with a
triple chain ring what limits are made to the shift pattern when on
the center ring? Assuming that the chain line through the center line
of the 5th cog, on a 9 speed cassette, and the center line of the
center chain ring?

It appears to me that considering the actual distance between the
three chain rings versus the actual distances on the cassette that the
center chain ring should be able to shift to any cog without problems.

John B. Slocomb
(johnbslocombatgmaildotcom)


I always like to think that the smallest sprocket must only be used
with the outer ring and the biggest sprocket must only be used with
the smallest ring. This help reduce the strains imposed on the
derailleur pulley spring(s) and sometimes is the only way to shift
cleanly over the entire range without having a drooping chain.
Depending upon your derailleur it might be as well to limit the mid
ring off the bottom two sprockets (if its a racing type der).
  #6  
Old July 16th 11, 07:11 PM posted to rec.bicycles.tech
RonSonic
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Posts: 2,658
Default Cross shiftting


"John B. Slocomb" wrote in message
...

"Cross shifting", i.e., Large chain Ring/large cassette cog or small
chain ring/small cog is generally taken as a mortal sin. But with a
triple chain ring what limits are made to the shift pattern when on
the center ring? Assuming that the chain line through the center line
of the 5th cog, on a 9 speed cassette, and the center line of the
center chain ring?

It appears to me that considering the actual distance between the
three chain rings versus the actual distances on the cassette that the
center chain ring should be able to shift to any cog without problems.


As far as the chain and rear der are concerned all the cogs are in play from
the middle ring.

Not all setups will run without the chain rubbing the front der cage or big
chainwheel. If you can trim the front der all's good.


  #7  
Old July 17th 11, 01:43 AM posted to rec.bicycles.tech
T°m [email protected]
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Posts: 813
Default Cross-Chaining

On 7/16/2011 7:30 AM, John B. Slocomb wrote:

"Cross shifting", i.e., Large chain Ring/large cassette cog or small
chain ring/small cog is generally taken as a mortal sin. But with a
triple chain ring what limits are made to the shift pattern when on
the center ring? Assuming that the chain line through the center line
of the 5th cog, on a 9 speed cassette, and the center line of the
center chain ring?

FYI - This is normally referred to as "cross-chaining".

It appears to me that considering the actual distance between the
three chain rings versus the actual distances on the cassette that the
center chain ring should be able to shift to any cog without problems.


Say screw it and get a Schlumpf bottom bracket and Rohloff hub.

watching for the delivery truck

--
Tºm Shermªn - 42.435731°N, 83.985007°W
I am a vehicular cyclist.
  #8  
Old July 17th 11, 03:24 AM posted to rec.bicycles.tech
[email protected]
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Posts: 2,322
Default Cross-Chaining

On Jul 16, 7:43*pm, "Tm [email protected]" ""twshermanREMOVE\"@THI
$southslope.net" wrote:
On 7/16/2011 7:30 AM, John B. Slocomb wrote:

"Cross shifting", i.e., Large chain Ring/large cassette cog or small
chain ring/small cog is generally taken as a mortal sin. But with a
triple chain ring what limits are made to the shift pattern when on
the center ring? Assuming that the chain line through the center line
of the 5th cog, on a 9 speed cassette, and the center line of the
center chain ring?


FYI - This is normally referred to as "cross-chaining".

It appears to me that considering the actual distance between the
three chain rings versus the actual distances on the cassette that the
center chain ring should be able to shift to any cog without problems.


Say screw it and get a Schlumpf bottom bracket and Rohloff hub.


Or a bent with very, very long chains g.
--D-y
  #10  
Old July 17th 11, 03:57 AM posted to rec.bicycles.tech
[email protected]
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Posts: 2,322
Default Cross shiftting

On Jul 16, 7:30*am, John B. Slocomb wrote:
"Cross shifting", i.e., Large chain Ring/large cassette cog or small
chain ring/small cog is generally taken as a mortal sin. But with a
triple chain ring what limits are made to the shift pattern when on
the center ring? Assuming that the chain line through the center line
of the 5th cog, on a 9 speed cassette, and the center line of the
center chain ring?

It appears to me that considering the actual distance between the
three chain rings versus the actual distances on the cassette that the
center chain ring should be able to shift to any cog without problems.


Sheldon Brown has a gear "visualizer", and there's another one called
"Gerz" that makes charting pretty easy.

It seems to me that with the 30/42/52 triple I have, run against 8sp
and 9sp cassettes with 13-23 or 14-26t cog spreads, you wind up with
gear ratios that favor running the two or three cogs most in line with
both the inner and outer rings, while the middle ring works over four
or five cogs, overlapping so to speak with the inner and outer rings
on one cog. It's been a few years, maybe I'm misremembering but I
think this "question" pretty much takes care of itself in practice if
you will.

Meaning, you're keeping the chain fairly straight while you use "same
ratios" (or close duplicates) of gears you might find by "crossing"
farther on any of the ring/cog combinations. Not to say you shouldn't
"be able" to use any cog/chainring combination without either drooping
the chain (which invites unshipping and/or dragging in the dirt) or
binding/breaking the rear derailleur due to too short a chain, but why
not use the chain in happier combinations?
--D-y
 




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