Which chain for a 5 speed Brompton?

[Slowroad]

The chain on my 1999 Brommie is stretched so I want to replace it. Usually I get a bike shop to do it but I should be able to do it myself. I've been sold a chain (it's one for 8-speed gears) but I noticed it is narrower than the one on my bike, so I did some googling and it seems that older Bromptons should have a 1/8" chain and newer ones 3/32". Is this correct and if so, should I be getting, say, a 5-speed chain?
Cheers!

[gregoryoftours]

If it's a 5 speed hub gear I would have thought you'd be better off with a proper single speed chain as it will last longer than a 5 or 8 speed chain, being thicker and more chunky. You only need a chain that isn't a single speed in a derailleur system where the chain needs to shift sideways onto different sprockets.

[Brucey]

your Brompton probably has a 1/8" sprocket fitted to it in which case only a 1/8" chain will fit. Of available 1/8" chains the KMC B1 is the best value because it is very hard-wearing, being a fully bushed chain, unlike most others, which are 'bushingless' construction.

A derailleur chain (eg 5,6,7,8,9s chain) is not the right thing for your bike.

cheers

[Slowroad]

Cheers - thought they seemed a bit absent-minded when they sold me the chain! Now I need to go and check how many teeth I've got to see how many links I need - not sure I just trust counting what's there already!

[pwa]

Cheers - thought they seemed a bit absent-minded when they sold me the chain! Now I need to go and check how many teeth I've got to see how many links I need - not sure I just trust counting what's there already!

I usually lay the new chain down on the garage floor alongside the old one, both stretched out. The old one will be a little "stretched" with the rivets slightly further apart, but I find that the easiest way to get the number of links the same. You need a rivet tool to take unwanted links off the new chain, and a joining link to join the ends when it's on the bike.

[Slowroad]

Cheers - thought they seemed a bit absent-minded when they sold me the chain! Now I need to go and check how many teeth I've got to see how many links I need - not sure I just trust counting what's there already!

I usually lay the new chain down on the garage floor alongside the old one, both stretched out. The old one will be a little "stretched" with the rivets slightly further apart, but I find that the easiest way to get the number of links the same. You need a rivet tool to take unwanted links off the new chain, and a joining link to join the ends when it's on the bike.

Yes, that's what I usually do, what I meant was that seeing as the shop sold me the wrong chain, maybe it also didn't get the last chain the right length seeing as it was them that changed it last time!

[rmurphy195]

This page useful? http://brilliantbikes.co.uk/94-chains

4th or 5th item down!

[Slowroad]

Useful! Also interesting in that it implies that you can replace your old 1/8th sprocket for a newer 3/32nd one. Now I wonder, on a 15 year-old bike, how I tell whether it's the original old one or a newer one! This is getting complicated!

[Brucey]

complicated? Not really.... a 1/8" chain is nearly always cheaper than a 3/32" one and if you get a fully bushed one (eg KMC-B1) it will last far longer. A 1/8" chain will run on both 1/8" sprockets and 3/32" ones, so just get a 1/8" chain and be done with it.

[NB If you want to run 3/32" chain you need both the chainset and the sprocket to accept the chain.]

Most 3/32" IGH sprockets look like this;



i.e. with a joggle near the centre (which is nothing to do with the dish or offset in the sprocket BTW), to bring the effective thickness at the centre near to 3mm (like 1/8" sprockets are). However this is not infallible; smaller 3/32" SA sprockets are sometimes flat. If you fit a flat centre 3/32" sprocket in place of a 1/8" one then you will likely need different spacers on the sprocket to stop it from rattling on the driver.

cheers

[Slowroad]

Cheers Brucey! Will get a KMC-B1 then. They are only about a fiver online.
[I did have to do some googling to find out what 'bushing' and 'non-bushed' meant - here's Sheldon Brown explaining it http://www.sheldonbrown.com/chains.html]

[LollyKat]

complicated? Not really.... a 1/8" chain is nearly always cheaper than a 3/32" one and if you get a fully bushed one (eg KMC-B1) it will last far longer. A 1/8" chain will run on both 1/8" sprockets and 3/32" ones, so just get a 1/8" chain and be done with it.

Interestingly the Sheldon Brown / John Allen link thinks the opposite:

Cyclists often speak of chain "stretch", as if the side plates of an old chain were pulled out of shape by the repeated stresses of pedaling. This is not actually how chains elongate. The major cause of chain "stretch" is wearing away of the metal where the link pin rotates inside of the bushing (or the "bushing" part of the inside plate) as the chain links flex and straighten as the chain goes onto and off of the sprockets. If you take apart an old, worn-out chain, you can easily see the little notches worn into the sides of the link pins by the inside edges of the bushings. With bushingless chains, the inside edge of the side plate hole that rubs against the link pin has a smooth radius instead of a sharp corner. This probably contributes to the greater durability of bushingless chains.

Or is it different for IGH and single speed chains?

[Slowroad]

Didn't I say it was complicated?
I daresay either bushed or bushless will be fine!

[Brucey]

Re bushed vs bushingless; if you look at the insides of a bushingless chain vs a fully bushed chain you can see that the bushingless chain will articulate more easily. Once articulated the two half-bushings each present one edge to the centre pin; the side plate on the outside of the bend presents a radiused edge to the pin and the side plate on the inside presents a sharp edge to the pin. The inside side plate shouldn't see as much load, so the sharp edge shouldn't cause terrible wear.

The idea that 'bushingless chains last longer' is not a universal truth; for many years now it has been the only kind of derailleur chain that you can buy, and for some years prior to that the only 3/32" fully bushed chain you could buy was cheap stuff where the bushings were not hardened anyway; it might be true in for derailleur chains, but it was hardly a fair comparison. [Today, nearly all chains are bushingless, including most 1/8" ones. If you want a fully bushed 1/8" chain at a reasonable price, you can choose KMC-B1, and, er, that is about it; pretty much all the other bushed 1/8" chains are now boutique items that (because of the spurious excuse that they might be NJS approved) are now sold for a small fortune....]

Bushingless chains can sometimes run more quietly and are more likely to have shaped inner side plates that can help keep a slack chain in place. They also have the advantage that lube will penetrate every part of the chain quite easily, but then so will dirt...

The total bushing area in a bushingless chain is smaller than in a bushed chain; there is normally a small gap between the inner side plates and in addition the radius detracts from the bushing length. On a 8s chain you could have about 5mm of bushing, but in a bushingless chain it is usually only ~2.5mm total length. This increases the loading and the wear, given like-for like materials, even in straight line loading. [To get acceptable life, the chain side plates need to be hardened differently vs bushed chains.]

If you look at 1/8" bushingless chain it is normally built using 3/32" side plates, but with a bigger gap between them because a wider roller is used. In this case a potentially ~6mm wide bushing is reduced to less than half of that in a bushingless construction. In straight-line loading, with like-for-like materials and lubes, it would be fairly reasonable to expect that the bushed chain would last twice as long.

Similar arguments apply to the interface between the roller and the inner side-plate external bushing surface. Whilst roller wear isn't the most important form of chain wear it does contribute to the premature failure of chains and sprockets.

It is notable that in other comparable chain applications (motorcycles, conveyors, chainsaws etc) they use fully bushed roller chains to the exclusion of almost all other types. [ There are a few applications for so called 'silent' Morse/HyVo chains, but these are less commonplace and somewhat specialised. ]

In fact as far as I know, bicycles are the only application for bushingless chain of the sort that is commonly used, and it is also the only application in which the sin of deliberate misalignment is routinely committed.

I am quite certain that manufacturing bushingless 1/8" chains suits bicycle chain manufacturers, because it is cheaper to make than fully bushed chain; there are two components fewer per full link (8 instead of 10), assembly is easier (several processes are eliminated), with fewer critical (interference fitting) tolerances to worry about, and all the parts of all the bicycle chains made in the same factory can use the same raw materials, the same hardening processes etc.

Such expediency does not, however, make it 'the right chain' for every bicycle. A decent fully bushed chain will last up to 20000 miles inside a chaincase, but because of its very much smaller bushing area, I would not expect a bushingless chain to last anywhere near the same mileage, no matter how clean/well lubed it is.

cheers

[LollyKat]

Many thanks, Brucey, for such a clear and detailed reply.

[Slowroad]

Second that!