why use 8-speed chains?

Anthony

Retrobike Rider
Isn't a 9-speed chain better and easier to get hold of?

Somebody please correct me if I'm wrong, but my understanding is that a 7/8-speed sprocket is the same thickness as a 9-speed sprocket, the only difference in the cassettes being how close together the sprockets are. And similarly all rings are the same thickness, so the slightly narrower 9-speed chain fits perfectly well onto 7/8-speed kit. It's also slightly lighter and of at least equal stiffness and strength, so it should shift easier and have the same durability.

So why do I find myself thinking I 'ought' to fit an 8-speed chain?
 
I have previously used a 9-speed chain with a chainset that was originally from a 7/8sp setup, and the chain had an annoying habit dropping down between the inner and outer chainrings (it was a double chainset, on a road bike) and getting jammed. After this had happened a few times I realised it was because a 9-speed chain is narrower so the spacing between the chainrings did not suit the width of the chain.

So I suppose that is one possible reason....
 
...I have also heard that 8-speed chains last longer although I'm not sure why? Presumably the plates are thicker but I thought it was the rollers that actually wear down not the plates.
 
your chain wears because it stretches, not because of the rollers or plates physically being erroded.

I think that the sprockets are actually a different width on 9 speed, but the same on 7/8. Hence use the right chain for your set up and you will encounter fewer shifitng issues.

Consult sheldon brown if unsure - he knows everything. :)
 
BarneyRubble":1vwuy0mz said:
your chain wears because it stretches, not because of the rollers or plates physically being erroded.

Sorry, not the case. The so-called stretch is the link pins wearing - a worn chain is much floppier from side to side. the bit that goes is where the link pin fits through the inner link, and the inner link faces.

If you take a badly worn chain apart you can see that the pins have a polished indentation on them.

As Sheldon says:
Chain "Stretch"
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 rivet 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 rivets by the inside edges of the bushings. With bushingless chains, the inside edge of the side plate hole that rubs against the rivet has a smooth radius instead of a sharp corner. This probably contributes to the greater durability of bushingless chains.
 
Just for LGF as he loves numbers

Chain Width
5.9mm = Shimano 10-speed
6.6mm = Shimano 9-speed
7.1mm= 7&8 speed chains most commonly

Shimano Sprocket Thickness
1.8mm 8 speed Shimano
1.78mm 9 speed Shimano
1.6mm 10 speed Shimano
 
FluffyChicken":bl5ix4do said:
Chain Width
5.9mm = Shimano 10-speed
6.6mm = Shimano 9-speed
7.1mm= 7&8 speed chains most commonly

Shimano Sprocket Thickness
1.8mm 8 speed Shimano
1.78mm 9 speed Shimano
1.6mm 10 speed Shimano
8-speed and 9-speed chains seem to be designated 3/32nds and 11/128ths respectively, i.e., 2.4mm and 2.2mm. It looks as though those are the widths of the rollers, so if a 2.2mm roller is big enough for a 1.78mm sprocket, I guess it's also big enough for a 1.8mm sprocket.
 

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