N
NeauDL
Guest
I had ridden an Ultegra triple with a 12-34 9 speed cassette extensively
without trouble on both Trek 5200 and Calfee Luna road bikes, and recently rode
a mountain century with an 11-34 cassette without trouble. But I wanted a
still lower gear, and put XTR 952 cranks on the road bike (Calfee Luna). These
have 26-36-48 chainrings. I did not change the Ultegra triple front derailleur
(It was moved downward on the seattube.) but the chain was shortened. Chain
and cassette had only 100 miles on them before cranks were changed, so
everything is brand new. However, I find I can't use all the cogs on the
cassette with the middle chainring. The three largest cogs, 26 and larger,
with the 36 tooth middle chainring result in pulling the chain off the middle
chainring onto the granny whenever a real load is applied (i. e. pushing hard
up a hill or standing). As far as I can tell, both cranks have a 47.5 mm front
chainline. (I have the shorter of the two available 952 bottom brackets.) Of
course, the spacing in the rear is road spacing (130mm) rather than mountain
bike spacing (135). On a mountain bike, the cassette would be farther out by
2.5 mm, but it looks like it would need to move more than that not to have a
problem, and obviously there's no problem with an 11-34 cassette on all modern
mountain bikes. Is this problem the result of both the small size of the 36
and the lack of mountain bike rear wheel spacing? Do others using smaller than
42 tooth middle chainrings on road bikes have similar problems with larger
cassettes? If I went back to the Ultegra and changed to 26-38-48 chainrings,
would I be likely to have the same problem? Any help would be much
appreciated, especially before the Markleeville Death Ride in July.
L. D. Lide
without trouble on both Trek 5200 and Calfee Luna road bikes, and recently rode
a mountain century with an 11-34 cassette without trouble. But I wanted a
still lower gear, and put XTR 952 cranks on the road bike (Calfee Luna). These
have 26-36-48 chainrings. I did not change the Ultegra triple front derailleur
(It was moved downward on the seattube.) but the chain was shortened. Chain
and cassette had only 100 miles on them before cranks were changed, so
everything is brand new. However, I find I can't use all the cogs on the
cassette with the middle chainring. The three largest cogs, 26 and larger,
with the 36 tooth middle chainring result in pulling the chain off the middle
chainring onto the granny whenever a real load is applied (i. e. pushing hard
up a hill or standing). As far as I can tell, both cranks have a 47.5 mm front
chainline. (I have the shorter of the two available 952 bottom brackets.) Of
course, the spacing in the rear is road spacing (130mm) rather than mountain
bike spacing (135). On a mountain bike, the cassette would be farther out by
2.5 mm, but it looks like it would need to move more than that not to have a
problem, and obviously there's no problem with an 11-34 cassette on all modern
mountain bikes. Is this problem the result of both the small size of the 36
and the lack of mountain bike rear wheel spacing? Do others using smaller than
42 tooth middle chainrings on road bikes have similar problems with larger
cassettes? If I went back to the Ultegra and changed to 26-38-48 chainrings,
would I be likely to have the same problem? Any help would be much
appreciated, especially before the Markleeville Death Ride in July.
L. D. Lide