5 Bolt Chainring Measurement Made Easy...

Chainrings are most often measured in reference to their Bolt Circle Diameter (BCD) depicted as B in the above picture. BCD is literally the diameter of an imaginary circle that connects the centers of all the chainring bolts. 
It is easier to measure the distance between adjoining chainring bolts as depicted by A in the above picture. Use the chart below to determine what size rings you have. All measurements are

74 BCD Rings: A = 43.5 mm, B = 74 mm

110 BCD Rings: A = 64.7 mm, B = 110mm

130 BCD Rings: A = 76.4 mm, B = 130 mm

135 BCD Rings: A = 79.5 mm, B = 135 mm

144 BCD Rings: A = 84.6 mm, B = 144 mm

2015 Campagnolo Chainrings

Campagnolo 11 speed chain rings - 2015

In 2015, Campagnolo introduced their new 4-bolt chainring design. This design allows a single crank to accomodate chainring sizes from "standard sizing" down to "compact sizing."

The possible combinations are 53/39, 52/36, and 50/34. The pairs are designed to work as a set and are not designed to be interchangeable.

Outer rings measure 146mm BCD, inner rings measure 112mm BCD. They are not compatible with any older chainrings.

Older Campagnolo Chainrings

Campagnolo chain ring compatibility

  • In 2005, Campagnolo introduced a compact crank to accomodate smaller chain ring sizes (i.e. 50/34). The rings use asymmetric 5 bolt, 110mm BCD design with the 5th hidden bolt at 112mm BCD. Therefore, you cannot use non-Campagnolo, symmetrical 5 bolt 110mm BCD chain rings.
  • All Campagnolo cranks from 1990 to 2008 use a 135 mm, bolt circle diameter, chain ring. To calculate BCD, measure from the center of any chain ring bolt to the center of the bottom bracket spindle, mounting hole. Then multiply by two and you will have the diameter of the bolt circle. Vintage Campagnolo cranks used a 144 mm BCD.
  • Campagnolo did not change their rings when they went from 8 to 9 speed. All 9 speed chain rings are 100% compatible with 6, 7 or 8 speed, 135 BCD crank sets.  Record, Chorus, Athena, Daytona and Centaur 8/9 and 10 speed silver inner rings are identical. Record 8/9 speed outer rings are identical to Chorus, Athena, Centaur and Daytona 8/9 speed outer rings except for the placement of the chain roll off pin and the countersinking of one bolt hole.
  • On Record and 2004 to 2008 Chorus, the roll off pin is next to a bolt hole; older Chorus, Athena, Centaur and Daytona has the roll off pin mid-way between two bolt holes.
  • Campagnolo changed their outer ring when they moved to 10 speed. It was milled on the backside so it would sit closer to the inner ring to accommodate the narrower 10 speed chain. In the photo below, the left ring is for 8/9 speed and the right ring is for 10 speed.
  • In some cases, your 10 speed crank will work just fine on your 8/9 speed drivetrain. Our recommendation is to try it first. Possible issues that come up are: 1. Rubbing on the large chainring when gear combination is small/small and 2. "floating chain" inbetween chainrings when shifting to small ring.
  • You may retrograde most 10 speed square taper cranks/chainrings to 8/9 speed drivetrain by simply adding a Le Tour chainring spacer to every chainwheel bolt behind/inside the outer 10 speed ring. If your square tape cranks have the four-arm spider with a hidden 5th bolt, remove the Campy 0.4mm spacer (below) from behind the crank arm and discard it. Then place the Le Tour spacer on top of the 3.7 mm hidden bolt spacer, as well as between the outer chainring at the four crank arm fingers.
Hidden bolt, 0.4mm spacer

Hidden bolt, 0.4mm spacer

  • ***Record and Chorus Carbon 135 BCD cranks from 2004-2006 lack the 0.4mm spacer and should not be spaced out this way. Alloy, Triple and CT carbon cranks are okay. See photo below***. The same goes for Ultra Troque cranks, which are lacking the 0.4mm spacer. Spacing as described above on these cranks would tilt the chainring at an angle. Instead, you could add the Le Tour spacers between small ring and spider arm to achieve similar spacing, but first make sure your front derailleur has room to move farther inboard, and that there's sufficient room between the inner chainring and chainstay.
  • All 10s Campagnolo middle and outer chainrings use steel chain pick up pins and have precisely machined teeth. Chain pick up pins are only used on middle (for triple cranks) and outer rings. They help to lift your chain when you are shifting from a smaller ring into a bigger ring. Note in the photo below how the teeth above the pick up pins are profiled to further assist in up shifting.
  • Veloce uses stamped and machined, aluminum alloy inner, middle and outer rings. These are only available as a set of two or three rings and are the same for 8,9 and 10 speed cranks. Veloce 10 speed crank arms, unlike Centaur, Chorus and Record, are milled 0.4mm thinner than Veloce 8/9 speed crank arms. Use Veloce chain rings to give new life at a bargain price, to an old Chorus, Athena, Daytona, Centaur, Veloce or Mirage cranks. You may also upgrade your Veloce or Mirage crank with Campy Chorus 8/9 speed outer and Record inner/middle rings.
  • Inner, middle and outer rings should be matched unless the difference in teeth is 10 or less. Campy does not make a 53 tooth 8/9 speed outer ring to match a 42 inner ring. However, we have used a 53 8/9 speed outer for a 39 inner, with a 42 tooth inner and the shifting was good.
  • Campagnolo 8/9 and 10 speed outer chainrings may be used with double or triple cranks as long as you match them to the proper middle and/or innermost chainring. E.g. a 53 tooth 10 speed triple outer ring can be used with a 42 tooth middle ring on a triple crank or a 42 tooth ring on a two ring crank.