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Discussion Starter · #1 ·
I currently have a Shimano Dura Ace FC-7900 crankset with 53/39 chainrings. They have a 5-bolt pattern; does this equate to 110mm? I have been considering using a compact or sub-compact. Can I simply swap out the chainrings and it will shift properly? Will I need to replace the crankset and/or bottom bracket and derailleur? What are my options?
 

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It's a 130mm BCD crank.

You can swap to a compact, IF your front derailer can relocate lower on the seat tube to accommodate the smaller rings, but you might need a new F derailers as well. Might as well do the b-bracket with the new crank.

Might be cheaper to find a cassette that starts in a 13 or so.
 

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'brifter' is f'ing stupid
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It's a 130mm BCD crank.

You can swap to a compact, IF your front derailer can relocate lower on the seat tube to accommodate the smaller rings, but you might need a new F derailers as well. Might as well do the b-bracket with the new crank.

Might be cheaper to find a cassette that starts in a 13 or so.
Good job not actually answering any of the questions. MMsRepBike got it right. If the OP's front derailleur won't go low enough for a compact due to the frame how is buying another front derailleur going to help?
 

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FYI Last I looked 6750 cranksets where pretty cheap and 7950 were not available anywhere I could find.
6750 would work fine with an otherwise DA group. I hear new 11 cranks work fine with 10 speed but don't know that for fact. 6750 is probably your best bet. I'm sure FSA and the like make something that'll work but Shimano cranks are better.

Regarding this "new F derailers as well" business. It's really hard to imagine a such thing as a frame that won't take a compact so I can't imagine that's an issue but with 7900 shifters you can't use another front der. They only work with 7900 front derailers.
I've tried. You can get another front der to shift but not without having a lot of rub. 7900 front ders are wider because of the no big ring trim.

Not to overcomplicate this. Just get a 6750 crank. Easy no big deal.
 

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I've found the cost of new rings is not much savings over buying a new crank anyway, so went with a new crank when I chose to go from compact to standard rings on Ultegra 6800 - if you are going to go compact and stay there, you can probably get enough from your existing crank to make the swap even less than it would have been if you could have changed rings to compact.
 

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Good job not actually answering any of the questions. MMsRepBike got it right. If the OP's front derailleur won't go low enough for a compact due to the frame how is buying another front derailleur going to help?
Do you really find it necessary to be a schmuck ?

You could instead be helpful by stating something along the lines of;

What Steve B. Is trying to say is the 7900 is a 130BCD crank so you cannot put 110mm bcd rings on it. That mostly leaves you with A) Changing the crank to a compact. The issues you might run into with this is 1) Since a compact crank might have 50/34 rings (common) you might need to lower the F derailer to get decent shifting and that begs the question of can you lower the derailer ?. Some braze-on mounts can limit how low you can move the derailer. 2) The shape of the existing derailer doesn't match the curve of the smaller 110BCD rings, so you might need a new F derailer as well. C) A new crank would probably want a new b-bracket as well.

Or B) Swap to a different cassette to get the lower gearing you want. Cheaper, but plan on a new chain if doing the cassette.

A post along these lines, expanding on the sparse info. I provided (I must have been in a testy mood), also points out to me that my post was sparse, yet says it in a nice way.
 

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I have used a 52 DA 7900 ring with a SRAM 38 t ring and didn't have any shifting issues. It's not a big change but my 58 year old legs notice the difference.

I also installed an Ultegra 50/34 6800 crank on an otherwise Ultegra 6700 bike and everything worked fine.
 

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A post along these lines, expanding on the sparse info. I provided (I must have been in a testy mood), also points out to me that my post was sparse, yet says it in a nice way.
Awwww, just give CXWrench a back rub and you will all be fine. :D
 

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Discussion Starter · #11 ·
Yeah, I'm getting kind of old myself, with a messed up back as well. I have previously switched the cassette to an 11-28 but I'm still having a bit of difficulty on some of the climbs in upstate/western NY. At times it will be a slow grind at 50-60rpm, hence the desire for a compact. Other times, I just think I need to get stronger... Thanks for all the great advice.
 

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Do you really find it necessary to be a schmuck ?
You're new around here aren't you? :)

That said, many of my posts are similarly acerbic, so I can't really throw stones.


Sent from my iPad using Tapatalk Pro
 

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'brifter' is f'ing stupid
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You're new around here aren't you? :)

That said, many of my posts are similarly acerbic, so I can't really throw stones.


Sent from my iPad using Tapatalk Pro
He sure is sensitive for being around longer than I have. You'd think he'd realize how this place works and just roll with it.
 

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He sure is sensitive for being around longer than I have. You'd think he'd realize how this place works and just roll with it.
Low tolerance for as*(deleted) is all.

You might note that I essentially and for the last week let my participation in the thread drop. That was me rolling with it.

Do we need to continue this thread hijack ?, I do believe the question was answered.
 
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