Horiz dropout / axle placement question

bicycle6228 said:

Campagnolo Record rear derailleur and Suntour Winner freewheel having
26T largest cog: Unless the rear axle is positioned almost at the
extreme rear of the horizontal dropouts, the derailleur's upper jockey
pulley's teeth contact the teeth of the 26T cog. With the axle
positioned as mentioned, two things happen that prevent this tooth
contact problem: 1) the freewheel center is further to the rear than
the jockey pulley; 2) the distance the chain must span from chainring
to cog is greater, causing the upper jockey pulley to be lower, due to
further CCW rotation of the jockey pulley assembly (viewed from drive
side).
I have the chain length as short as possible to still allow 52T CR /
26T cog usage, though I never use this combo.
I guess one result is a longer wheelbase, which doesn't bother me
unless someone convinces me it should cause concern. The other
possible result relates to mechanical integrity. If it matters, this
bike is used for commuting and towing a trailer. I'm not a heavy or
particularly strong rider, but I often carry up to 10 LBS on a rear
rack plus pull the trailer. In the last 3 years, I've had two steel
frames develop cracks in the drive side chain stay near the BB shell:
one was a 30 year old Peugeot U08, the other was an unknown vintage,
unknown maker steel frame allegedly made in Switzerland.
Here's the question: Does positioning the rear axle at or near the
rear limit of horizontal dropouts have any impact on durability of the
bicycle overall?
Any advice or comments greatly appreciated. If nothing else, perhaps
I've amused the group with my retro / entry level componentry.

Nope, what we do for larger cogs, proper chain length, and rder w/o a
b l;imit screw-as long as the dropouts are parallel-no problema.

many of us ride this older stuff everyday.....like I do on my Gunnar
and Merckx..no click shifting, brifter stuff for me!!!

bicycle6228 said:

Campagnolo Record rear derailleur and Suntour Winner freewheel having
26T largest cog: Unless the rear axle is positioned almost at the
extreme rear of the horizontal dropouts, the derailleur's upper jockey
pulley's teeth contact the teeth of the 26T cog. With the axle
positioned as mentioned, two things happen that prevent this tooth
contact problem: 1) the freewheel center is further to the rear than
the jockey pulley; 2) the distance the chain must span from chainring
to cog is greater, causing the upper jockey pulley to be lower, due to
further CCW rotation of the jockey pulley assembly (viewed from drive
side).
I have the chain length as short as possible to still allow 52T CR /
26T cog usage, though I never use this combo.
I guess one result is a longer wheelbase, which doesn't bother me
unless someone convinces me it should cause concern. The other
possible result relates to mechanical integrity. If it matters, this
bike is used for commuting and towing a trailer. I'm not a heavy or
particularly strong rider, but I often carry up to 10 LBS on a rear
rack plus pull the trailer. In the last 3 years, I've had two steel
frames develop cracks in the drive side chain stay near the BB shell:
one was a 30 year old Peugeot U08, the other was an unknown vintage,
unknown maker steel frame allegedly made in Switzerland.
Here's the question: Does positioning the rear axle at or near the
rear limit of horizontal dropouts have any impact on durability of the
bicycle overall?
Any advice or comments greatly appreciated. If nothing else, perhaps
I've amused the group with my retro / entry level componentry.

Your classic Record 1020 (or N Record 1020a?) was rated for a '28t low
gear' when freewheels were 14~28 and fronts were 49-51 or similar. On
more modern 10-tooth fronts (42-52), a 24t low is the practical limit of
dependably good response. With a 26t as you discovered, the lack of a
top pivot spring or a "B" screw makes setup touchy. Possible but not
straightforward.

There's no problem doing what you describe - optimizing axle position
for best shifting. Removing the adjuster screws may give you more room.
Sometimes a spot of weld on the end tab's face to bring the changer back
slightly helps. I note you set chain length to a minimum. Set it to a
maximum for best shifting - as much as it will hold without taking the
paint off the chainstay. (At 26t, min and max chain may be the same length!)

Absolutely do not run a gear train with insufficient chain to shift into
the big-big. You'll remember not to do that until you are tired, then
you will absentmindedly shift that combination to your chagrin.
--

Andrew Muzi
www.yellowjersey.org
Open every day since 1 April, 1971