You have just ordered a chainring to replace your worn outer ring. It arrives, you try to fit it — and the bolt holes do not line up. Order to redo, return to manage, extra delay. The number one cause of this very common mistake? The wrong BCD.
BCD — Bolt Circle Diameter — is the technical parameter that governs all road bike chainring compatibility with its crankset. Yet it is rarely explained clearly, and too often reduced to a single line in a spec table. This guide fixes that: definition, 4-step measurement method, full table of all road standards, compatibility by brand and groupset, and the common mistakes you absolutely must avoid.
Table of contents
- What is BCD (bolt circle diameter)?
- How to measure your chainring BCD in 4 steps
- Road bike BCD standards
- BCD 110 mm: the modern compact standard
- BCD 130 mm: the old double standard
- BCD 135 mm: the Campagnolo standard
- BCD 107 mm: SRAM AXS
- Cross-compatibility table by groupset
- Fitting a chainring from a different brand than your crankset
- Common mistakes to avoid
- FAQ — Road bike chainring BCD
1. What is BCD (bolt circle diameter)?
BCD — Bolt Circle Diameter — is the diameter in millimetres of the imaginary circle that passes through the centre of each chainring bolt hole on the crankset spider. You may also see it written as PCD (Pitch Circle Diameter) in European catalogues — it is exactly the same concept, two names for the same value.
In practice, BCD is the one absolute technical constraint when choosing a chainring: if the chainring BCD does not match the crankset BCD, the bolts will not align and fitting is impossible. Two chainrings of different tooth counts but with the same BCD are freely interchangeable. Two chainrings of the same tooth count but different BCDs are completely incompatible.
4-arm or 5-arm: the formula is not the same
A road crankset spider can have 4 or 5 arms. Modern road cranksets (Shimano 105, Ultegra, Dura-Ace since 2012; all SRAM groupsets) are almost exclusively 4-arm. Older standard double and triple cranksets are 5-arm.
This distinction matters because the distance between bolts does not give you the BCD directly in the same way depending on the number of arms:
- 4-arm crankset: measure the distance between two opposite bolt holes (directly across from each other). This distance equals the BCD directly.
- 5-arm crankset: measure the distance between two adjacent bolt holes (next to each other), then multiply by 1.701 to get the BCD.
2. How to measure your chainring BCD in 4 steps
Two methods let you find your crankset BCD without removing the chainring.
Method 1 — Read the reference engraved on the crank arm (30 seconds)
This is the fastest method. Look at the inner face of your right crank arm: the crankset reference is engraved there (e.g. FC-R8000 for a Shimano Ultegra R8000, FC-RED for a SRAM Red). From this reference, simply check the manufacturer's technical specifications on their website or in the manual to find the BCD. As a general rule:
- Shimano FC-R7000 / R7100 / R8000 / R8100 / R9000 / R9100 / R9200 → 110 mm 4-arm
- Shimano FC-6700 / 7900 / 6800 (older Ultegra/Dura-Ace generations) → 130 mm 5-arm
- SRAM Rival / Force / Red (mechanical) → 110 mm 4-arm
- SRAM Red AXS / Force AXS / Rival AXS → 107 mm 4-arm
- Campagnolo Chorus / Record / Super Record (post-2015) → 110 mm 4-arm (compact) or 135 mm 5-arm (standard)
Method 2 — Manual measurement with a ruler (2 minutes)
If you do not have the reference or it is unreadable, measure directly. A millimetre ruler is sufficient — a vernier calliper gives an even more accurate reading.
- Identify the number of spider arms (4 or 5).
- 4-arm: measure the distance between the centres of two opposite bolt holes. Note the value in mm.
- 5-arm: measure the distance between the centres of two adjacent bolt holes. Multiply by 1.701. Note the result.
- Compare to the conversion table below.
| Measured distance (4-arm, opposite holes) | Corresponding BCD | Configuration |
|---|---|---|
| 64.7 mm | 110 mm | Modern compact road (Shimano / SRAM 4-arm) |
| 76.4 mm | 130 mm | Standard 5-arm road (Shimano / SRAM older generation) |
| 79.4 mm | 135 mm | Campagnolo standard 5-arm |
| 62.8 mm | 107 mm | SRAM DUB AXS (modern groupsets) |
| 84.7 mm | 144 mm | Track (piste) |
| 43.5 mm | 74 mm | Triple — inner chainring (5-arm) |
| 55.3 mm | 94 mm | Triple — middle chainring (5-arm) |
Tip: if your measurement differs slightly from the theoretical value (e.g. 65 mm instead of 64.7 mm), round to the nearest value. A small discrepancy of a few tenths of a millimetre is normal with a standard ruler.
3. Road bike BCD standards
The road market is structured around four active standards and a few legacy standards still found on vintage bikes or second-hand parts. Knowing them lets you check compatibility at a glance.
| BCD | Arms | Main brands | Compatible tooth counts | Status |
|---|---|---|---|---|
| 110 mm | 4 | Shimano (105, Ultegra, DA since ~2012), SRAM (Rival, Force, Red mechanical) | 34 to 52 T | Dominant current standard |
| 107 mm | 4 | SRAM DUB AXS (Rival AXS, Force AXS, Red AXS) | 33 to 54 T (and above) | Modern AXS standard |
| 130 mm | 5 | Shimano (Ultegra 6700, DA 7900 and older), SRAM 5-arm | 38 to 53 T | Legacy — very common on existing bikes |
| 135 mm | 5 | Campagnolo (Chorus, Record, Super Record standard) | 39 to 53 T | Campagnolo exclusive |
| 110 mm | 4 | Campagnolo (compact, post-2008) | 34 to 50 T | Campagnolo compact |
| 144 mm | 5 or other | Track cranksets — Shimano, Rotor, TA | 46 to 56 T | Track only |
| 74 mm | 5 | Triple cranksets (inner chainring) | 24 to 36 T | Triple — virtually gone from new bikes |
| 94 mm | 5 | Triple cranksets (middle chainring) | 30 to 50 T | Triple — virtually gone from new bikes |
4. BCD 110 mm: the modern compact standard
The 110 mm 4-arm is today the dominant standard on the road market. It equips all recent Shimano cranksets — from the FC-5800 (105, 2014) to the latest R9200 (Dura-Ace 12s) — and all SRAM mechanical cranksets (Apex, Rival, Force, Red in non-AXS versions).
Its main advantage over the 130 mm: it allows chainrings down to 34 teeth as the inner ring, or even 32 teeth from certain brands (Stronglight, Spécialités TA). This is what made compact 50/34 and semi-compact 52/36 configurations possible, now standard on virtually all modern road bikes.
110 mm 4-arm chainrings are produced by a very wide range of third-party manufacturers: Stronglight, Spécialités TA, Miche, Rotor (Q-Rings, QXL, noQ), Osymetric, AbsoluteBLACK… It is the easiest standard to replace, with the widest choice of tooth counts and materials. For more on compact and semi-compact configurations, see our article on double and triple road bike chainrings.
5. BCD 130 mm: the old double standard
The 130 mm 5-arm was the universal road standard for over 20 years. It is found on all Shimano cranksets predating 2012 (Ultegra 6700, Dura-Ace 7900 and earlier generations) and equivalent SRAM 5-arm cranksets. It remains very common on the existing bike fleet.
Its main constraint: the large spider diameter imposes a minimum tooth count of 38 teeth for the inner chainring. It is impossible to fit a 34 T or 36 T ring — the spider arms would physically interfere with the chain. This is why cyclists riding in the mountains with 130 mm cranksets often compensate with a wider-range cassette.
130 mm chainrings are still produced by several brands (Shimano as spare parts, Stronglight, Spécialités TA, Miche), but the choice of available tooth counts is more limited than in 110 mm.
6. BCD 135 mm: the Campagnolo standard
Campagnolo has historically used a 135 mm BCD on its standard double cranksets, where Shimano and SRAM used 130 mm. This 5 mm difference makes Campagnolo 135 mm chainrings incompatible with Shimano and SRAM cranksets, even though both have 5 arms — the bolts simply will not align.
For compact Campagnolo cranksets (110 mm 4-arm, introduced from 2008), theoretical compatibility with Shimano/SRAM 110 mm chainrings exists but there are mounting subtleties — notably the bolt offset which may differ. Specialist brands such as Spécialités TA and Miche offer chainrings explicitly compatible with Campagnolo with the correct mounting profiles.
In 2015, Campagnolo introduced a new BCD standard for its Ultra-Torque and Power-Torque modern groupsets (145 mm on some models) — always check the datasheet for your exact groupset before buying a Campagnolo chainring.
7. BCD 107 mm: SRAM AXS and modern groupsets
Since the launch of SRAM AXS electronic groupsets (Red AXS, Force AXS, Rival AXS), SRAM has introduced a new BCD standard: 107 mm 4-arm on its DUB AXS cranksets. This standard is incompatible with 110 mm chainrings from previous generations.
Practical consequences: if you buy a SRAM AXS groupset and want to fit third-party chainrings (Rotor Q-Rings oval chainrings, for example), you must ensure the manufacturer offers a version specifically in 107 mm BCD. Rotor does offer chainrings in 107 mm BCD for DUB AXS spiders — but not all brands have yet updated their range.
In 2024, SRAM also launched a Red AXS version for chainrings of 54 teeth and above — a configuration aimed at criterium racing and speed events. One to watch if you are moving towards very large chainrings.
8. Cross-compatibility table by groupset
This table centralises BCD compatibility information for the most common road groupsets. It lets you check at a glance which BCD corresponds to your drivetrain before buying any chainring.
| Brand | Groupset / Model | BCD | Arms | Min/max tooth count | Speed |
|---|---|---|---|---|---|
| Shimano | 105 R7000 / R7100, Ultegra R8000 / R8100, Dura-Ace R9100 / R9200 | 110 mm | 4 | 34–52 T | 11s / 12s |
| Tiagra 4700 | 110 mm | 4 | 34–52 T | 10s | |
| Ultegra 6700, Dura-Ace 7900 and older | 130 mm | 5 | 38–53 T | 10s and older | |
| SRAM | Apex, Rival, Force, Red (mechanical) | 110 mm | 4 | 34–52 T | 11s |
| Rival AXS, Force AXS, Red AXS (DUB) | 107 mm | 4 | 33–54 T | 12s | |
| Campagnolo | Chorus, Record, Super Record (compact, post-2008) | 110 mm | 4 | 34–50 T | 11s / 12s |
| Chorus, Record, Super Record (standard, 5-arm) | 135 mm | 5 | 39–53 T | 10s / 11s |
Important note: chainrings designed for an 11-speed drivetrain are not back-compatible with a 12-speed chain, and vice versa. The 12s chain is narrower and tooth profiles differ. Always check the speed count in addition to the BCD.
9. Can I fit a chainring from a different brand than my crankset?
Yes, in the vast majority of cases — and it is often recommended to access intermediate tooth counts that the original brand's range does not offer. A Stronglight, Spécialités TA, Miche or Rotor chainring can perfectly fit a Shimano or SRAM crankset, provided three cumulative criteria are met:
- Identical BCD: the absolute constraint — see the table above.
- Identical number of arms: a 5-arm chainring will not fit a 4-arm spider, even if the BCD is close.
- Speed compatibility: an 11s chainring may not work correctly with a 10s or 12s chain. Check the chainring datasheet.
Practical example: you have a Shimano Ultegra R8000 crankset (110 mm, 4-arm, 11s) and want to fit a 38-tooth inner ring for better climbing — a tooth count Shimano does not offer. The Spécialités TA X110 or Stronglight 38 T 110 mm allow this swap, explicitly designed for Shimano 11s cranksets with 110 mm 4-arm.
Special case: the asymmetric FSA 110 mm
Some FSA cranksets use a 110 mm BCD but with an asymmetric bolt offset — one arm is positioned differently. Although the BCD is identical, some standard third-party chainrings may not fit correctly. FSA offers its own chainrings and certain third-party brands (Spécialités TA FX110) develop versions specifically compatible with FSA. Always look for the mention "FSA compatible" in the technical datasheet if you have this type of crankset.
10. Common mistakes to avoid
| Common belief | Reality |
|---|---|
| "Shimano 110 mm BCD and MTB 104 mm BCD are the same thing" | FALSE. 104 mm is the most common MTB standard (4-arm); 110 mm is the road standard. A 6 mm difference — completely incompatible. Never mix road and MTB standards. |
| "My crankset has 4 arms and 110 mm BCD, so all 110 mm chainrings will fit" | PARTLY FALSE. The BCD must match, but so must the speed count. A 12s chainring may not work correctly with an 11s chain. Check both criteria. |
| "Campagnolo and Shimano both have 5 arms, so they must be compatible" | FALSE. Campagnolo standard = 135 mm, Shimano standard = 130 mm. Five arms in both cases, but different BCDs — the bolts will not line up. |
| "I can fit a 34 T chainring on my 130 mm crankset" | FALSE. The minimum tooth count on a 130 mm 5-arm crankset is 38 T. Below that, the spider arms physically interfere with the chain. Only 110 mm BCD allows 34 T and below. |
| "My SRAM AXS groupset is 110 mm BCD, same as older SRAM mechanical" | FALSE. SRAM DUB AXS cranksets use 107 mm BCD — not the 110 mm of mechanical SRAM groupsets. Always check the exact groupset model. |
| "A third-party chainring (Rotor, Stronglight…) will never be as good as an OEM one" | FALSE. Third-party manufacturers such as Stronglight, Spécialités TA and Rotor offer chainrings of equivalent or superior quality, often CNC-machined from 7075 aluminium, and give access to intermediate tooth counts not available in the original range. |
Find a chainring compatible with your crankset
Once you have identified your BCD, browse our selection of road bike chainrings — Stronglight, Spécialités TA, Shimano, Rotor — compatible with all common BCD standards (110 mm, 130 mm, 135 mm). If you need to replace your chainring, see also our complete step-by-step guide.