Bike chainrings

chainrings Fixes, Reviews & Guides

Embedded thumbnail for Front Derailleur Setup with an Oval Chainring

Front Derailleur Setup with an Oval Chainring

Do you have any tips for installing oval chainrings and fine tuning the front derailleur for their use?

Before beginning, it is important to not that front derailleurs will never shift as...

Tools hex wrench
Company: Rotor
Type: Repair Tutorial
Embedded thumbnail for Review: SRAM Force CX1 (1x11 group)

Review: SRAM Force CX1 (1x11 group)

A quick look at SRAM's new Force CX1 1x11 group:

1x11 groups, with 1 chain ring in the front and an 11-speed cassette in the back have gained wide popularity in all styles of mountain...

Company: SRAM
Type: Review
Embedded thumbnail for Install a RaceFace Narrow/Wide Single Chainring

Install a RaceFace Narrow/Wide Single Chainring

RaceFace’s new chainring has a narrow/wide narrow tooth profile. It retains the chain without the need of a guide or a keeper, and it’s reducing some weight.

Look at...

Company: Race Face
Type: Repair Tutorial

The chainrings are one or more sprockets that transfer power from the crankset to the cassette via the chain.

Chainrings

More gears helps cyclists keep the same cadence at many different speeds. Depending on the type of bike, it may need one, two, or three chainrings. Road and mountain bikes use a range of speeds and have a need for many gear combos. Some genres like BMX, downhill, and hardtails have just one chainring. They save on weight, and have lighter profiles for neat tricks and stuff.

Chainrings can range from about 20 to 55 teeth, and can be constructed from aluminum alloys, steel, titanium, or carbon fiber.

The teeth on chainrings with multiple sprockets are usually cut in a way that helps move the chain shift. The middle chainring shifts up and down, so it usually has ramps on either side, while the highest chainring will only shift down. Its teeth only have ramps to one side. The chain will be set down on and picked up from the smallest cog, so it usually has the least amount of shape on its teeth.

Chainring tooth angle

Chainrings attach to the crankset by what is called a spider (arms extending from the drive side crank arm). On cheaper bikes, the crankset is one piece, and sometimes the chainrings are welded directly to the crank arm! When the chainring wears out, the whole crankset needs to be replaced. Other scenarios have a pin on the drive side crank arm that inserts into the chainring, providing the power.

Drive pin and hole

With more expensive bikes however, the chaining bolts to the spider, making replacements easier and obviously more affordable. These can be either four or five bolt. Why two systems you ask? Mountain bikes have big scary chainrings that might flex under heavy load, so the thicker frame and rigidity is needed. Other bikes conserve weight and opt for four bolt chainrings.

Chainring bolts  Chainring bolting to crank

 

Inexpensive chainrings are either just welded directly to the spider (the arms with which the chainring attaches to the bottom bracket) or have a hole where a pin on the crank arm powers the ring. One-piece cranksets are very interchangeable and therefore very cheap. They are compatible with many sizes of chainrings you can find for dirt cheap at your local bike shop. One reason this design isn't so popular is because it applies loads differently while riding, and can be very hard on bottom bracket cups.

Pin hole in one

Multi-piece cranksets are heavier, but are easier on the bottom bracket.

All the pieces

Most good quality chainrings are between $100 and $200, while some can be several hundreds of dollars more. High-end chainrings have bolt holes which they attach to the spider. Chainrings with 4 or 5 bolts are the most common. 

Multi piece crankset ring Smooth chainring

Chainrings can really take a beating. If it isn't rocks and debris smashing or chipping the teeth on the cogs, they could snap if the chain shifts under heavy load. 

Chipped tooth

If you find a bent or broken tooth on the chainring, don't sweat. Repairs can be quick and easy. To get the bolts off to detach the crank from the spider, it's likely only a hex wrench or screwdriver is needed. If replacing any of the middle chainrings, the crank arms will need to come off. Fetch yourself a crank puller.

Chainrings have a lot of statistics. To save time, tears, and money, order the right chainring. How many bolts does it use? What's the bolt center diameter? Do you want the same number of teeth on the new sprocket? 

bcd chainrings

If it's only the big chainring that needs to be replaced, thank your lucky stars. Sometimes, the big sprocket can be replaced without even taking the crank arms off. 

  • Slip the chain down off the chainring to the base of the crank arm.
  • Remove the bolts fastening the large chainring to the spider and slide it off.
  • Replace the new chainrings and bolt to the spider.

Cassette style chainrings

If you're replacing a double or triple chainring, the crank arms need to come off.

bolt locations

  • Use a crank puller to remove the whole assembly from the bottom bracket.
  • With the chainring off, remove chainrings. Usually they will come off in order, smallest to largest.
  • Replace all spacers and chainrings in the right order. The flat side of the chainring faces to the outside. The teeth face inside to help the chain jump cog to cog.
  • Reassemble the crankset.

checking that chainring bolt

Some chainrings have tension requirements on their bolts, which might require a torque wrench. Securely fasten all bolts on the chainring and reattach the chain.

Chainrings vary in size from 20 teeth to 55 teeth. On bikes with more than one chainring, the sprockets are ordered largest on the outside to smallest on the inside. This helps the chain from falling off while riding. Chainrings have several key measurements:

Chainring thickfreakness

Width - The thickness of the chainring. 

  • 3/16" (4.76mm) - Applies to older bikes (skip-tooth designs) and big BMX chainrings
  • 1/8" (3.18mm) - Many standard track, BMX, cruiser bikes, 1 and 3 speed bikes
  • 3/32" (2.38mm) - Most road cycles, hybrids, mountain bikes, single speed, and bikes with 5, 6, or 7 speeds.
  • 5/64" (1.98mm) - Any bike with 9, 10, or 11 speeds

BCD (Bolt Circle Diameter) - The diameter of the circle made by the stack bolts on the inner chainring. Normally you would measure from the center of one hole across the center of the chainring to another hole. The problem is that so many common chainrings have odd numbered bolts and therefore the bolt holes are not aligned for this measurement to be so easy. To find the BCD, we measure C-C, and make a calculation to account for the number of bolts.

C-C (Distance between adjacent bolts) - Measured from the center of one bolt hole to the center of the next.

NOTE: Because the "center" of the hole isn't there, you may decide to use the edge of the bolt hole for this measurement. Just be consistent.

Bolt circle diameter

The center to center distance is different between chainrings that use 3, 4, 5 and 6 bolts. To finally determine the bolt circle diameter (BCD), multiply the C-C as such:

  • 3 bolt C-C x 1.155
  • 4 bolt C-C x 1.414
  • 5 bolt C-C x 1.701
  • 6 bolt C-C x 2.000

BCD boyyy


                              Common 5 bolt chainring sizes and applications 
BCD (mm) Smallest Ring Center-Center (mm) Application
151 44 88.8 Pre-1967 Campagnolo standard (now obsolete)
144 41 84.6 Old Campagnolo standard, still used in track bikes
135 39 79.5 Current Campagnolo standard
130 38 76.4 Standard outer chainring on road bikes
128 38 75.2 Obsolete
122 38 71.7 Stronglight 93, 101, 103, 104, 105 (obsolete)
118 36 69.4 Ofmega, SR (obsolete)
116 35 68.2 Old Campagnolo (obsolete)
110/112 34 64.7 Campagnolo CT inner/middle/outer with one bolt at larger diameter behind crank
110 33 64.7 Touring double, standard triple outer
100 31;36 73.6 Merz adapter; Campagnolo triple (obsolete)
94 29 55.4 Compact triple outer
92 30 53.3 Shimano Dura-Ace triple inner
90 32 52.9 Edco, Mavic triple inner
86 28 50.5 Stronglight 80,00,100, some SR triples (obsolete)
74 24 43.5 Standard ("full-sized") triple inner. Used with 110mm, 130mm or 135mm rings
58 20 34.3 Compact granny gear
56 20 32.9 Sun Tour compact granny gear

 

                Common 4 bolt chainring sizes and applications
BCD (mm) Smallest Ring Center-Center (mm) Application
146 44 103.2 Shimano XTR M960 outer
112 34 79.2 Shimano XTR M950, M952 middle/outer
104 32 73.6 Shimano XTR M960, XT, LX outer
102 32 72.1 Shimano 2003 XTR middle
68 22 48.1 Shimano XTR M950, M952 inner
64 22 45.3 Shimano XTR M960, XT, LX inner
58 20 41.0 Sugino MX350 inner