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"Compact Double Crank" = "Touring Bike Crank"



 
 
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Old June 3rd 05, 04:35 AM
Sheldon Brown
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Default "Compact Double Crank" = "Touring Bike Crank"

David Huggins-Daines wrote:

I wonder why the move to integrated granny spacers happened. I can't
see any benefit in it, for the consumer at least.


There are several benefits:

Easier to change chainrings, because you don't need to deal with loose
spacers.

Better thread engagement for the mounting bolts.

You can use shorter mounting bolts.

Probably also permits the spider arms to be made thinner and lighter
since the holes don't go as far through them.

There is also a drawback; it makes it harder to customize the spacing.

For instance, my "Brown" has a nice old Sugino AP130 crank (this was, I
believe, the first 130/74 crank ever. I recall being very excited when
I got it because if finally allowed me to do a triple with full-sized
Biopace chainrings. (It is set up with 52-42-28.)

I wanted the chainline of the two big rings to be in the normal range
for a double crank, so I used much thinner than normal spacers to attach
the 28 tooth chainring.

The idea is that 99% of the time I ride it as if it were a 52-42 double,
but when I'm really up against it I have the 28 ring in reserve. For
many years I rode this with a 12-22 6-speed freewheel. The 28 tooth
chainring could only run smoothly with the 2 or 3 largest sprockets, but
there was no reason to ever use any of the other sprockets with the 28
anyway.

The skinny spacers (and a Phil Wood adjustable bottom bracket) allowed
me to get the crank in very close to the frame for usable chainline in
all combinations using the two larger rings.

This could be difficult to do now, because I'm not sure any modern front
derailer has sufficient leftward travel to shift it, but the old Sun
Tour Cyclone handles it OK.

Sheldon "Breaking The Rules" Brown
+----------------------------------------------+
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Phone 617-244-9772 FAX 617-244-1041
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