Campy Chorus chainring question

[PacMan]

So I want to replace the inner ring on my Campy Chorus crankset--from a 44t to a 39t. I know I need a 135mm, 10 speed compatible. But I'm seeing 5 Bolt/4 arm and 5 Bolt/5 arm and the chainrings look the same.

How do I figure out which one I need?? What's the difference when they look identical in the pics I'm finding online?

5 Bolt/4 Arm:



5 Bolt/5 Arm:



They look the same to me.

[Pickettt]

Campy 5 bolt/5 arm technically has six arms...it's hard to explain, but it works like this; if your crank has 5 equal arms PLUS the crank arm itself, it's a 5 bolt/5 arm. If, however, your crank arm forms the fifth arm of the spider (a chainring bolt threads into the back of the crank arm), you have a 5 bolt/4 arm. If you look at any Record crank over the last 10 years, they are all 5 bolt/4 arm. Hope this helps.

[SAR_boats]

39 is the standard gearing for non-compact cranks. If the BCD is the same then you is golden

[PacMan]

I believe I need the 5 arm then. I guess including a pic would've helped.

Originally Posted by SAR_boats

39 is the standard gearing for non-compact cranks. If the BCD is the same then you is golden

The cranks were given to me (along with the rest of the Chorus drivetrain), so I don't know the reasoning behind why the previous owner was running a 53/44. He was also running an 11/23 cassette--which was killing me on climbs. I replaced that with a 12/27. I would still like to drop back down to a 39t so I actually have a granny for steep climbs.

[SAR_boats]

Originally Posted by PacMan

I believe I need the 5 arm then. I guess including a pic would've helped.






The cranks were given to me (along with the rest of the Chorus drivetrain), so I don't know the reasoning behind why the previous owner was running a 53/44. He was also running an 11/23 cassette--which was killing me on climbs. I replaced that with a 12/27. I would still like to drop back down to a 39t so I actually have a granny for steep climbs.

Measure from one of the chainring bolts to the center of the crank and double that number, that is your BCD. Then just get a 39 tooth chainring that is 5-bolt 5 arm with the same BCD. For non-compact campy chorus it should be 135mm. Compact is 110mm

BTW, I wish I had friends that would give me a Chorus drivetrain.

[PacMan]

Originally Posted by SAR_boats

Measure from one of the chainring bolts to the center of the crank and double that number, that is your BCD. Then just get a 39 tooth chainring that is 5-bolt 5 arm with the same BCD. For non-compact campy chorus it should be 135mm. Compact is 110mm.

The chain rings say 135mm on them, so I'm sure that's the size I need.

Originally Posted by SAR_boats

I wish I had friends that would give me a Chorus drivetrain.

. Then I won't mention that I got the complete build (Campy Chorus, Mavic Open Pro wheels) given to me and all I had to do was provide a frame and fork. Oh wait, I just mentioned it.

[Pickettt]

Yes, that is a 5 arm/5 bolt.