102 and 104mm BCD Chainrings

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This topic has 8 replies, 5 voices, and was last updated 13 years ago by nedrapier.

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102 and 104mm BCD Chainrings
paulrockliffe
Free Member

Why do both sizes exist?

There’s no way a 102mm chainring would fit a 104mm spider is there?

I know I should have checked, I remembered it was just over 100mm I wanted, and assumed there would only be one standard close to 100mm.

Cheers

Posted 13 years ago

jonb
Free Member

Never heard of 102mm bcd.

Are you using a shimano crank with a non shimano ring. I singlespeeded a deore crank and had to do a little bit of filing to get a standard 104bcd ring to fit. Shimano make their cranks in a way that many non shimano rings do not fit without modification.

Posted 13 years ago

dhrider
Free Member

104mm is the standard BCD of most 4 arm cranks.

102mm is XTR M960 inner as far as I can remember, the middle and outer were 146mm.

You cannot fit a 102mm on a 104mm or vice versa. Some rings will need the tabs filed slightly to fit on certain crank arms but generally they will fit.

Posted 13 years ago

FGF 701 The Hydrate Or Die Edition

Stoner
Free Member

the only 102mm were M960 XTR I think.

http://www.wiggle.co.uk/shimano-102-bcd-xtr-m960-middle-chainring/

Posted 13 years ago

paulrockliffe
Free Member

This is the ring I bought:

http://www.chainreactioncycles.com/Models.aspx?ModelID=17275

Looks perfect for what I want it for, though I should have checked the size of it. So this would only work on XTR cranks then. Great. Why would $himano do this?

Posted 13 years ago

dhrider
Free Member

Yes, that ring is 102mm for XTR M960 only.

You need one that says 104mm in the blue text where the buy button is.

Posted 13 years ago

paulrockliffe
Free Member

Yep, annoying, will get onto it….

Posted 13 years ago

nedrapier
Full Member

thread resurrected through the wonders of serach.

I’ve got a 1999 vintage LX chainset with a wierdo spider thing. i’m absolutely certain it’s a 102 bcd for the middle chainring.

I’d planned to take a hacksaw to it, take off the outer, clean up the inner and use it with UN72 I’ve got hanging round on a singlespeed.

What are the chances of finding a 4 arm 102bcd, 46-48T, 1/8″ chainring?

No joy after a while googling. Any ideas?

Am I in moon/stick territory again?

Posted 13 years ago

nedrapier
Full Member

i’m absolutely certain it’s a 102 bcd for the middle chainring.

Ha. Erm.

Just measured it again and it’s very definitely 104mm. Must have used one of those shonky foreign rulers last time.

Posted 13 years ago