robbyrocks12345

One of my feinds gave me this old, Ross Eurosport? Only thing it needs is a chain and tires, I've replaced chains before but there's no old broken chain to compare it to for sizing. I have a chain tool and know how to relplace it, but I don't know what size to buy. Could I just get a larger chain with a masterlink and take other links out till it fits or is there a specific size? If it helps it's an 18 speed probaly from the late 70s-early80s.

Doconabike

There are two things to know about proper chain size - width and length.

The first is the width of the chain. A general rule is "skinny chain for lots of gears, wider chain for fewer gears (or internal gears or single speed)." You can pick the width of the chain on most bikes by just buying the chain width to match the number of gears on the cassette. For example, look at this page from Velo Orange https://store.velo-orange.com/index.p...ts/chains.html You just pick the width of chain for the type of cassette you have.

If you really want to know the details, chains are sized by inside roller width (3/32", 1/8", 5/32" or 3/16" roller widths). 3/32" inside rollers are narrow inside for modern cassettes. The thicker inside roller widths are for older bikes, single-speed bikes, internal-geared bikes, etc. Among the 3/32" inside roller width chains, you can buy a 7.2mm outside width chain for a 5,6, 7 or 8speed bike, a 6.8mm outside width chain for a 9 speed bike, or a 6.2mm outside width chain for a 10 speed bike. The nice thing is you don't have to know these details. You can walk into a bike store and ask for a "chain for a bike with 27 speeds." They will hand you the box that says "bicycle chain, 9-speed." (you don't have to know that this chain will have an inner dimension of 3/32" inside rollers and 6.8mm outside width).

The next decision is the length of the chain. Most chains come a bit longer than needed for the average bike. The typical new chain has 112 to 116 links. You then take out a few links to make it fit your bike. Look at the link to Sheldon Brown for instructions on setting the right chain length for your bike. https://sheldonbrown.com/derailer-adjustment.html#chain

So, a typical modern bike (29 speeds) would need a "9-speed" width chain (to fit the 9-speed cassette on back) and would have the length adjusted as per Sheldon's instructions. My old beater would need something like the KMC Z-50 (to fit the 7-speed cassette on back), then I would adjust the length as per Sheldon's instructions.

I hope this helps.

fietsbob

Some older mountain bikes, I have one, needs a few extra links added to the chains in the box..

I get a few extra links from my LBS when I get a new chain,
more of the same "Speed"/width and brand.
5,6,7,8 is all using the same chain these days, 9 a different one..

HillRider

Since it's an "18-speed" from that period it's 3 chainrings and 6 cogs right? If so, then the chain you need will be labled 7/8-speed or just 8-speed meaning it's for freewheels or cassettes with 7 or 8 cogs but it will fit your bike just fine.

As noted, most chains come a bit longer than required and you remove the extra links. A chain that comes with a master link (SRAM and KMC are the most widely distributed brands) makes joining the chain easier but the Shimano specific joining pin also works well. Just be sure to read the direction sheet that comes with whatever chain you buy. Also, go to the Park Tools web site and look up their tutorial on chain sizing and installation.

Finally, a new chain on an old worn freewheel or cassette is very likely to skip under load. You may have to replace the freewheel also to get smooth operation.