Granny gear conversion (23 to 27)



Wayno

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Sep 2, 2006
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I've just got a new light pair of wheels and decided to get a 12-27 cassette (from a 12-23) so I can spin up hills better.

Question: Do I need a new chain? ie lengthen it? Re-adjust rear and front derailleurs?

OR just put them on and ride those hills?

wayno
 

John M

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Jun 21, 2005
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Wayno said:
I've just got a new light pair of wheels and decided to get a 12-27 cassette (from a 12-23) so I can spin up hills better.

Question: Do I need a new chain? ie lengthen it? Re-adjust rear and front derailleurs?

OR just put them on and ride those hills?

wayno

You should be fine on chain length unless your chain was cut to the minimum length that would work for the drivetrain. If the old cassette/chain are pretty worn, you might need a new chain anyway.

No FD or RD adjustments are usually necessary if the cassette is the same brand as the one you are replacing.
 

gclark8

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Apr 13, 2004
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The chain will be OK, I assume the crankset is 39/53 or similar.

39+27=66 teeth
53+15=68 teeth, the middle of the cassette range in the big ring.

Just ride it! :)
 

Wayno

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Sep 2, 2006
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Extra 4 teeth on the rear cassette and no change to chain length?

I'll give it a go

Thanks
 

John M

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Jun 21, 2005
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Wayno said:
Extra 4 teeth on the rear cassette and no change to chain length?

I'll give it a go

Thanks
Should be OK unless your chain is already too short or nearly too short. Even if it is on the short side, it will be fine if you avoid the big chainring/big cassette cog combo.
 

Retro Grouch

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Dec 29, 2005
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Wayno said:
I've just got a new light pair of wheels and decided to get a 12-27 cassette (from a 12-23) so I can spin up hills better.

Question: Do I need a new chain? ie lengthen it? Re-adjust rear and front derailleurs?

OR just put them on and ride those hills?

wayno
I think that all of the previous posters have given you bad advice. Always, always, always check chain length when installing either a larger chainring or a larger cassette.

It's possible to ride for years with a too short chain and not even know it. Then some nice day you'll be cruising along in your big front chainring and go to shift down a cog to crest a hill. SURPRISE!!! You have just attempted to shift into the big/big with a too short chain. The weakest part to give is the derailleur arm which has twisted into your spokes. You now need a new derailleur, new rear wheel, new chain and maybe even a whole new frame. You also need a ride home.

Checking is easy so it's really stupid not to check. With your bike in the bi chainring gently try to shift onto the big cog. If it goes and you can still feel a little extra give on your derailleur arm, you're good-to-go. It it doesn't, you need a longer chain.
 

Wayno

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Sep 2, 2006
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Retro Grouch said:
I think that all of the previous posters have given you bad advice. Always, always, always check chain length when installing either a larger chainring or a larger cassette.

It's possible to ride for years with a too short chain and not even know it. Then some nice day you'll be cruising along in your big front chainring and go to shift down a cog to crest a hill. SURPRISE!!! You have just attempted to shift into the big/big with a too short chain. The weakest part to give is the derailleur arm which has twisted into your spokes. You now need a new derailleur, new rear wheel, new chain and maybe even a whole new frame. You also need a ride home.

Checking is easy so it's really stupid not to check. With your bike in the bi chainring gently try to shift onto the big cog. If it goes and you can still feel a little extra give on your derailleur arm, you're good-to-go. It it doesn't, you need a longer chain.
You were right Retro Grouch.

The chain was long enough but was worn and did not engage all the gears properly. I was shocked that after only 1300km the chain had stretched so much.

You are wise oh Retro one :)
 

Albert 50

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Apr 18, 2006
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Wayno said:
I was shocked that after only 1300km the chain had stretched so much.

You are wise oh Retro one :)
I'd say it's almost imposable to wear a chain in that distance unless maybe you rode in mud & slush on a MB or your bike is a kmart huffy :) [or was that chain put on old, already worn out rings & cassette :eek: ]