How many BCDs "standards" are there between Campagnolo 11 and 12?

[slowpoke]

- 5 bolt (pre 2015 Campy 11)
  - 135mm "standard"
  - 110/112 compact with hidden proprietary bolt
- 4 bolt (2015 11sp groups)
  - 146/112
- 4 bolt (H11 + 12 speed groups -- see Mark's comment below)
  - 146/112
- Chorus 12
  - 96 (to get low for 48/32)
- Super Record Wireless
  - 121/88 BCD (to go lower for 45/29)

Does that sum things up? Not counting Ekar in the mix, but feel free to add it.

[Mark McM]

Ekar is the same BCD as the Chrorus 12spd outer chainring.

The 4 arm 146/112 BCD chainrings are slightly different between 11spd and 12spd leading to some compatibility issues. Specifically, there is a circumferential step on the outer surface of the outside chainring, and the ends of the spider arms fit within this step. The spider arms on 11spd cranks are slightly shorter, so the step is at a slightly smaller diameter on 11spd chainrings, and the 12spd spider arms are slightly longer, so the step is at a slightly larger diameter on 12spd chainrings. The upshot is that 11spd 146 BCD chainrings don't fit on 12spd 146 BCD cranks. (H11 chainrings have the larger step diameter of 12spd chainrings. so 12spd chainrings will fit H11 cranks, but standard 11spd chainrings won't).

[slowpoke]

Ugh, thanks Mark. Didn't realize there was yet another gotcha.

Any idea if Centaur 11 is with "old" 11 shorter arms, or H11 + 12 speed?

[Mark McM]

Originally Posted by slowpoke

Ugh, thanks Mark. Didn't realize there was yet another gotcha.

Any idea if Centaur 11 is with "old" 11 shorter arms, or H11 + 12 speed?

I'm afraid I don't know about Centaur 11.

But there's another gotcha regarding 135mm and 110/112mm BCDs: All "hidden 5th arm" cranks (all UT and PT cranks) have the chainrings bolted to 4 spider arms, and the 5th bolt attaches the chainrings to the back of the crank arm. This means that for the outer chainring, the chainring seats against the outside face of the spider arms, but seats against the inside face of the mounting flat on the back of the crank arm. Because the outer chainring seats against both inside and outside surfaces, the chainring has to be correct width - if it is not, then the chainring will warp when the mounting bolts are tightened. Unfortunately, there are two different chainring widths, depending on the model of the crank. Record/Chorus/Athena cranks are designed to use 3.5mm wide chainrings, while Centaur/Veloce/Mirage cranks are designed to use 2.7mm chainrings, which means outer chainrings are not interchangeable between these two groups of cranks.

[AngryScientist]

Unfortunately with more recent campy, it's been my experience that if you need a new chainring, or you want to change chainring size, you're almost always better off just buying a whole different crankset.

Very limited aftermarket support of campy bcd chainrings either.

I hope they will settle down with the newest SR bcd allowing a wide range of chainrings, but who knows.

[cgolvin]

Originally Posted by AngryScientist

Unfortunately with more recent campy, it's been my experience that if you need a new chainring, or you want to change chainring size, you're almost always better off just buying a whole different crankset.

Agree. I broke a tooth on my big (48) Chorus ring, ended up buying a used crankset and selling the crankset sans rings on eBay. Cost me a lot less than buying a new chainring. I would have considered switching to Zayante carbon cranks but it's quite a PITA to make those work with an ITA BB.