Brompton parts guide

Which chain does my Brompton need?

Bromptons use three different chains depending on the model and gearing, and the length depends on your chainring. Find your bike below, count two numbers, and the tables give you the exact part.

A Line or C Line 1, 2, 3 or 6-speed · 16" wheels. Most Bromptons made before 2026, including the classic M and H types. 8-speed chain, 3/32" → P Line, T Line, or 4 / 12-speed C Line 4-speed or 12-speed · 16" wheels · including Electric. C Line moved to this system in 2026. 10-speed SL Advance chain → G Line 20" wheels, introduced 2024. G Line chain →

First, count two numbers on your bike

1 · Chainring teeth

The big ring by the pedals. The size is usually stamped on it (44T, 50T, 54T…). If not, count the teeth. Most Bromptons are 50T; -12% gearing models are 44T; +8% models are 54T.

2 · Largest rear sprocket

The cog(s) on the rear wheel. Count the teeth on the biggest one. 3-speeds usually have a 13T; 6-speeds and 2-speeds have a 16T as their largest.

Quick answer

Your Brompton

Chainring

A Line & C Line — 1, 2, 3 and 6-speed

These bikes use an 8-speed, 3/32-inch chain made for Brompton by SRAM. It comes with a PowerLink so the chain can be removed and refitted without a chain tool. Four lengths exist; pick yours by chainring, then by largest rear sprocket. We stock the equivalent KMC X8 chain in bulk and cut it to any of the four lengths free — order it and choose your length under Shorten to fit my bike.

Chainring	Largest rear sprocket	Chain you need	Which bikes
44T	12T, 13T or 14T	96 link KMC X8, cut to 96 · also Brompton QCHAIN096DRReduced-gearing (-12%) 3-speed and single-speed	Reduced-gearing (-12%) 3-speed and single-speed
44T	15T or 16T	98 link KMC X8, cut to 98Reduced-gearing (-12%) 6-speed	Reduced-gearing (-12%) 6-speed
46T	13T	96 link KMC X8, cut to 96 · also Brompton QCHAIN096DRVery old original chainring — it is probably worn out; consider replacing it too	Very old original chainring — it is probably worn out; consider replacing it too
50T	12T, 13T or 14T	98 link KMC X8, cut to 98Standard 3-speed — the most common Brompton	Standard 3-speed — the most common Brompton
50T	16T	100 link KMC X8, cut to 100Standard 6-speed · reduced-gearing 2-speed	Standard 6-speed · reduced-gearing 2-speed
54T	12T, 13T or 14T	100 link KMC X8, cut to 100Increased-gearing (+8%) 3-speed	Increased-gearing (+8%) 3-speed
54T	15T or 16T	102 link KMC X8, cut to 102Standard 2-speed · increased-gearing (+8%) 6-speed	Standard 2-speed · increased-gearing (+8%) 6-speed

Replace the rear sprocket(s) at the same time. Chain and sprockets wear together. A new chain on a worn sprocket will usually skip under load — Brompton recommends changing both, and so do we.

Older 1-speed and 3-speed Bromptons originally came with a wider 1/8-inch chain; the 3/32-inch chain above now fits every A Line and C Line. If your bike is much older and you're not sure, bring it in or send us a photo of the chain's markings.

P Line, T Line & 4 / 12-speed C Line

The 4-speed and 12-speed drivetrain uses a 10-speed chain (Brompton's "SL Advance", made by YBN). The right length depends on your chainring and whether the bike is geared or single-speed. We stock 102, 104 and 106-link chains; bikes that need 98 or 100 links get a 102 that we shorten before it ships — pick Shorten to fit my bike on the product page. This applies to the P Line and T Line, the Electric P Line (from 2023) and the C Line and Electric C Line (from 2026).

Chainring	Gearing	Chain you need
44T	4‑speed / 12‑speed	102 link, shortened to 100
50T	4‑speed / 12‑speed	SL Advance 102 link
50T	Single‑speed	102 link, shortened to 98
54T	4‑speed / 12‑speed	SL Advance 104 link
54T	Single‑speed	SL Advance 102 link
56T	4‑speed / 12‑speed	SL Advance 106 link
56T	Single‑speed	SL Advance 102 link

Not sure of your chainring? P Line and T Line ship with 50T or 54T; the 56T is a T Line upgrade ring.

G Line

The 20-inch-wheel G Line (2024 onward) uses its own chain. It ships with a 54T chainring, and the length changes if you fit a smaller ring to lower the gearing. It takes a 9-speed chain: we stock the KMC X9 in bulk and cut it to length free — order it and choose your length under Shorten to fit my bike.

Chainring	Chain you need	Note
54T	114 link KMC X9, cut to 114	As delivered from Brompton
50T	112 link KMC X9, cut to 112	If you've swapped to 50T for lower gearing
44T	110 link KMC X9, cut to 110	If you've swapped to 44T for even lower gearing

Chains and other G Line parts are in our G Line section.

Good to know

Sprockets and chain wear together. On any Brompton, fit new rear sprocket(s) with the new chain or the new chain will likely skip.
A chain checker is cheap insurance. Replacing a chain at 0.5% stretch saves the sprockets and chainring; wait until it skips and you'll be replacing all three.
Changed your chainring? The length changes with it — use the table for your new ring, not the one the bike came with.
Still not sure? Email a photo of your chainring and rear sprocket to info@clevercycles.com, or bring the bike by — we can measure and fit it while you wait.

Frequently Asked Questions

How do I know which chain my Brompton takes?

Three things decide it: which drivetrain family your bike is (A Line / C Line hub gears, the 4- or 12-speed P Line / T Line system, or G Line), the number of teeth on your chainring, and the number of teeth on your largest rear sprocket. Count those two numbers, then use the quick-answer picker or the tables above. If you'd rather not count, email a photo of your chainring and rear sprocket to info@clevercycles.com and we'll tell you.

Can I use any 3/32-inch chain on my Brompton?

On 1-, 2-, 3- and 6-speed A Line and C Line bikes, yes: any good 8-speed 3/32-inch chain works, as long as it's the right length. The Brompton-branded chain (made for them by SRAM) comes pre-cut to the four factory lengths and includes a PowerLink, so you don't need a chain tool. 4-speed and 12-speed bikes (P Line, T Line and the 2026-on C Line) are different: they need a narrower 10-speed chain, which is the SL Advance.

My older Brompton has a wider 1/8-inch chain. Do I need to find another one of those?

No. Early 1-speed and 3-speed Bromptons shipped with a 1/8-inch chain, but the current 3/32-inch chain fits every A Line and C Line, old or new. Pick the length from the hub-gear table by chainring and largest sprocket. If your bike is very old and you're not sure what it has, bring it by or send us a photo of the chain's side plates.

Do I need to replace the rear sprockets when I replace the chain?

Usually, yes. Chain and sprockets wear into each other, and a new chain on a worn sprocket will typically skip under load. Brompton recommends replacing the rear sprocket (or the 2- and 6-speed pair) with the chain, and that's what we do in our workshop. The chainring lasts several chains, so it only needs replacing if its teeth are visibly hooked.

How do I know when my chain is worn out?

Use a chain-wear checker, which is a few dollars and takes ten seconds. Replace the chain at 0.5% wear and your sprockets and chainring will last much longer; ride it until it starts skipping and you'll usually be replacing all three. Regularly wiped and lightly lubed chains last far longer, especially through a Portland winter.

I swapped my chainring. Does the chain length change too?

Yes. A bigger ring needs a longer chain and a smaller ring needs a shorter one, on every Brompton family. Use the table row for the ring you have now, not the one the bike left the factory with. Going from the standard 50T to the 44T reduced-gearing ring on a 3-speed, for example, takes you from the 98-link chain to the 96-link.

Can you shorten the chain, or fit it for me?

Both. Some 4- and 12-speed setups need a 98- or 100-link SL Advance chain that Brompton doesn't sell; on the SL Advance chain page choose Shorten to fit my bike and we'll cut a 102 to length before it ships. If you're in Portland, bring the bike in: we can measure, fit the chain and sprockets while you wait, and check the rest of the drivetrain at the same time.