Chainrings

 

PCD Explained

PCD = Pitch Circle Diameter. It's the diameter of the circle that the chainwheel bolts are on.

It's also commonly called the Pin Circle Diameter (as in chainwheel pin, as it fits the abbreviation).

Also known as BCD (Bolt Circle Diameter)

If you get a chainring with the wrong PCD, it won't fit.

As well as different PCDs, chanwheels can use 4 bolts (mountain bikes) or 5 bolts (most road bikes).

This table lists the common PCDs, with rough conversions to a bolt-to-bolt measurement to make it easy to work out what PCD you're dealing with.

PCD

 Bolt to Bolt

 Comments

 64mm (4-bolt)  45mm  Current standard MTB inner chainring
 74mm (5-bolt)  43mm  Old triple crankset inner ring
 80mm (4-bolt)    This is used by SRAM/Truvativ on some of their double MTB cranksets (inner chainring)

 94mm

(4-bolt)

   Used on some SRAM cranks/chainrings.
 94mm (5-bolt)  55mm  Short-lived triple middle & outer. 8-speed Deore LX (also in 110mm)
 104mm (4-bolt)  74mm

 Current standard MTB middle and outer ring. An important variable within this standard is the inner diameter of the chainring (the support-ramp diameter of the spider). This is either 88mm or 90mm and both diameters can appear on the same crankset (different for middle or outer ring). This applies to Shimano, SRAM/Truvativ and RaceFace cranksets. Very difficult to predict - you'll just have to measure, even though this is difficult for the middle chainring.

Some middle chainrings from Shimano are made of carbon fibre and steel and as the carbon gives them great rigidity they don't use a support ramp on the spider, so the inner diameter of these is not important (though it measures up at about 82mm).

 110mm (5-bolt)  65mm  Shimano compact road and Campagnolo compact road. Also was used on old MTB cranksets before the 104mm standard took over.
 120mm (4-bolt)    This is used by SRAM/Truvativ on some of their single and double MTB cranksets (outer chainring)
 130mm (5-bolt)  76mm  Shimano road but the 110mm standard is taking over. Minimum chainring size of 39T.
 135mm (5-bolt)  79mm  Campagnolo Road
 144mm (5-bolt)  84mm  Old Campagnolo Road and (if I'm not mistaken) current Campagnolo Track.

 

 

Chainring Inner Diameters

There is a variable in mountain chainrings apart from number of teeth, bolt circle diameter, number of gears and (sometimes relevant) brand. The inner edge of the chainring will be either 88mm or 90mm in diameter (matches the support ramp diameter of the crankset). This is easily measured when the chainring is off the crank, and is also easily measured for the outer chainring while the ring is still on the crank. But be aware that Shimano did at one stage make a crankset that had one ramp diameter for the outer chainring and another for the middle chainring. So, to ensure compatibility, measure carefully.

 Crank Model  Middle Chainring  Outer Chainring
 Raceface  90mm  88mm
 Shimano FC-M410  88mm  
 Shimano FC-M510  90mm  
 Shimano FC-M572  90mm  
 Shimano FC-M582  88mm  
 Shimano FC-M760  88mm  88mm
 SRAM X-5 Triple  90mm  
 SRAM X-O Triple  90mm  
     

 

 

Chainwheel Screws BMX (Set 5)

FSA Chainring 36T 5 Arm 110mm

Shimano FC-3403 Chainring 39T 9x3 Sora

Shimano FC-6700 Chainring 39T 10x2

Shimano FC-M361 8sp Chainring 32T

Shimano FC-M411 Chainring 8sp 28T

Shimano FC-M430 Chainring 32T 9sp

Shimano FC-M540 9sp Chainring 32T

Shimano FC-M590 9sp Chainring 44T Grey

Shimano FC-M660 Chainring 32T 9sp SLX

Shimano FC-M660 Chainring 9sp 44T

Shimano FC-M770 XT Chainring 24T 10sp

Shimano FC-M770 Chainring 42T 10sp XT

FC-M770 22T

Shimano FC-M770 9sp Chainring 22T

Shimano FC-M780 Chainring 32T 10sp

Shimano FC-M785 Chainring 38TAK

Shimano FC-M8000 Single Chainring 32t

Truvativ Chainring 22T 10sp Triple X0

SRAM Chainring 33T 10sp Triple X0

SRAM Chainring 38T 10x2 104

SRAM Chainring 39T 10sp Double GXP X0

Steel Chainring BMX 36T Chrome

Steel Chainring BMX 44T Steel Blk

cw spacer

Step Collar 22.2mm to 23.8mm

Truvativ Chainring 22T Alloy