Replacing a 9s Shimano Crankset (Fc-M770) with a 10s on (Fc-M780)

Kostis

New member
I still have and love my old race MTB bike which runs a 9s drivetrain system. My Fc-M770 crankset is getting old and wondered if I could use a 10s FcM-780 without chaining any other element in the drivetrain. Could I use the middle and inner chainring from a Fc-M770 (I still have some spares)? Lastly, should i stick to the 9s chain or change to a 10s one? (I've read your informative article on chain compatibility). Thanks much!!
 
Solution
I still have and love my old race MTB bike which runs a 9s drivetrain system. My Fc-M770 crankset is getting old and wondered if I could use a 10s FcM-780 without chaining any other element in the drivetrain. Could I use the middle and inner chainring from a Fc-M770 (I still have some spares)? Lastly, should i stick to the 9s chain or change to a 10s one? (I've read your informative article on chain compatibility). Thanks much!!

Hi Kostis,

You could swap your 9-speed triple cranks for 10-speed triple cranks without noticeable problems. You might notice some chain rub when cross chaining (depending on how long your chainstays are - the shorter, the more is the drivetrain "sensitive" to cross-chaining), if the...
I still have and love my old race MTB bike which runs a 9s drivetrain system. My Fc-M770 crankset is getting old and wondered if I could use a 10s FcM-780 without chaining any other element in the drivetrain. Could I use the middle and inner chainring from a Fc-M770 (I still have some spares)? Lastly, should i stick to the 9s chain or change to a 10s one? (I've read your informative article on chain compatibility). Thanks much!!

Hi Kostis,

You could swap your 9-speed triple cranks for 10-speed triple cranks without noticeable problems. You might notice some chain rub when cross chaining (depending on how long your chainstays are - the shorter, the more is the drivetrain "sensitive" to cross-chaining), if the chainrings are a bit more narrowly spaced (this, if it happens, can be fixed by adding some washers, or by not riding severely cross-chained in the first place :) ).

Note:
The thing to look out for is how many teeth your largest chainring has. If your FD is nicely matching your existing cranks, it would be good to stay within a +- 2 teeth count with the new cranks.

Not sure how well I've explained this, but I tried to explain it with pictures in the 3rd chapter of the FD compatibility article.

I would also expect the chainrings to be closely-enough matching for you to not have any problems, they should have the same BCD of 104.
Front chainring mounting standards (BCD and bolt count) explained.

Regarding the chain, for as long as you're running a 9-speed cassette, you can use a 9-speed chains (despite the cranks being "10-speed"). Having said that, know that a 10-speed chain will also work perfectly fine with that setup (so I'd go with whatever comes cheaper).

Relja
 
Solution
Hi Kostis,

You could swap your 9-speed triple cranks for 10-speed triple cranks without noticeable problems. You might notice some chain rub when cross chaining (depending on how long your chainstays are - the shorter, the more is the drivetrain "sensitive" to cross-chaining), if the chainrings are a bit more narrowly spaced (this, if it happens, can be fixed by adding some washers, or by not riding severely cross-chained in the first place :) ).

Note:
The thing to look out for is how many teeth your largest chainring has. If your FD is nicely matching your existing cranks, it would be good to stay within a +- 2 teeth count with the new cranks.

Not sure how well I've explained this, but I tried to explain it with pictures in the 3rd chapter of the FD compatibility article.

I would also expect the chainrings to be closely-enough matching for you to not have any problems, they should have the same BCD of 104.
Front chainring mounting standards (BCD and bolt count) explained.

Regarding the chain, for as long as you're running a 9-speed cassette, you can use a 9-speed chains (despite the cranks being "10-speed"). Having said that, know that a 10-speed chain will also work perfectly fine with that setup (so I'd go with whatever comes cheaper).

Relja
That's an awesome reply Relia!
Thanks much and congratulations for your site and the knowledge base you have accumulated for all of us!
Take care,
Kostis
 
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