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Old 01-15-10, 11:19 PM   #1
billydonn
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A vs B Chainring?

Looking to replace the middle chainring on an Ultegra 9-speed tripple of 2004 vintage and I see A and B type rings listed. What's the difference and which do I need? I'm replacing 42t with 39t ring. Thanks...
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Old 01-15-10, 11:53 PM   #2
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Ideally, you want to use rings that all have the same letter. They're designed to shift harmoniously to/from eachother.
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Old 01-16-10, 12:02 AM   #3
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Quote:
Originally Posted by billydonn View Post
Looking to replace the middle chainring on an Ultegra 9-speed tripple of 2004 vintage and I see A and B type rings listed. What's the difference and which do I need? I'm replacing 42t with 39t ring. Thanks...
"A" and "B" chainrings are doubles. Sheldon Brown to the rescue:
http://www.sheldonbrown.com/gloss_aa-l.html#a with this addition: 53's are "B".

If you want a 39-tooth middle triple, you need this ring:
http://harriscyclery.net/product/ult...r6656-qc49.htm
or the equivalent.
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Old 01-17-10, 03:15 PM   #4
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As mech says, it's about how they shift together. And there are many more codes than A and B. See the chart in this post for a sample.
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