chain length

[onthe-edge]

Hi all, I have a 7speed set up on my bike and I've just replaced the chain, the thing is it's clearly marked as 7s, but it's a good 2ins. shorter than the original.
All seems ok and I cannot see any obvious problem, but can anyone offer any reason why I shouldn't carry on using it as it worries me a little that it may cause
a later 'wear'problem if I continue to ride with it. thanks daveT

 

[Andy-Mat]

Hi all, I have a 7speed set up on my bike and I've just replaced the chain, the thing is it's clearly marked as 7s, but it's a good 2ins. shorter than the original.
All seems ok and I cannot see any obvious problem, but can anyone offer any reason why I shouldn't carry on using it as it worries me a little that it may cause
a later 'wear'problem if I continue to ride with it. thanks daveT

Without a few pictures, each mentioning which gear (I would say top and bottom might be enough), its difficult to be certain as to whether it might be OK or not!
I often order my chains by the number of links, so I have never had that problem.
Also, wen I have seen a good offer, I have even ordered longer chains and removed the extra links....that works for me personally.
If you still have the old chain, count the number of links (I assume that was correct), use that value with your order.
Even adding a few links to a short chain is not really a problem either....
regards
Andy

 

[Deleted member 25121]

You old chain will have stretched, count the number of links to compare new and original.

 

[sjpt]

The 7 is about the width of the chain; 7 speed cogs are spaced further apart so can use a wider (often stronger) chain. You shouldn't have an issue with length as long as you can go from smallest front/smallest back, and also largest front/largest back with the derailleur taking up the slack and not rubbing. You shouldn't use those combinations in normal riding anyway as it puts the chain line at an angle which increases wear, so you can get away with those not working quite right in those extreme combinations if you are confident you won't choose them by mistake.

 

[onthe-edge]

Thanks for your input fellas, just to add to my confusion I've done a bit more digging and come up with what seems to the right choice, but it's still a bit shorter than the original. The old chain is 122 links ! the best replacement it seems is 114 links and that's for a 6/7/8 speed gear train. KMC make nothing specific for 7speed ebikes, but another site says needing an ebike specific chain is a myth and to just use a regular chain.
my chain ring has 46 teeth with a Shimano 7speed cassette. Can't take any pics because I'm changing the bottom bracket and have no crank on the bike at the moment. Think this chain will be ok ?

 

[sjpt]

Does the old chain behave on smallest front ring to smallest back ring. It sounds long for a conventional bike. Is it the original chain ... maybe when it was fitted whoever did it forgot to shorten it to the correct length? Sounds as if you can't check with the bottom bracket and crank off the bike.

The old one may well have stretched so it isn't sensible to use it any more, but that amount of stretching will be at most equivalent to a couple of links. The number of links isn't critical as long as the rear derailleur can cope. When you have the crank back on put on the old chain and set to biggest ring to biggest ring. Then see if you can pinch links together to simulate shortening the chain; as you pinch out more links eventually the chain will be tight and the derailleur will have run out of slack. That is probably 2 or 4 links too tight. Also try smallest to smallest and see if the derailleur is able to keep the chain relatively straight (not taut); if not it was too long.

An 8 speed chain should be fine on a 7 speed cassette.

 

[Andy-Mat]

Thanks for your input fellas, just to add to my confusion I've done a bit more digging and come up with what seems to the right choice, but it's still a bit shorter than the original. The old chain is 122 links ! the best replacement it seems is 114 links and that's for a 6/7/8 speed gear train. KMC make nothing specific for 7speed ebikes, but another site says needing an ebike specific chain is a myth and to just use a regular chain.
View attachment 31927my chain ring has 46 teeth with a Shimano 7speed cassette. Can't take any pics because I'm changing the bottom bracket and have no crank on the bike at the moment. Think this chain will be ok ?

Due to different sizes of frame and design, there can be differences in chain length between bikes, though they generally tend to be fairly similar IMHO.
If the 122 length chain was original, I myself, would tend to replace it with the same number of links, just to err on the safe side, assuming that the bike manufacturer knew what he was doing!
Simply adding a short length should be simple to do with the right tools and the removable link.
Also, the longer chain will wear ever so slowly, slower I feel.....
Also, if you carry the right equipment, you could possibly repair a broken chain simply by removing a few links, by the roadside....as a "get you home method!"
A spare link, though rarely needed, could be invaluable....
Some bikes are sold with no removable link nowadays in their chains, its a one piece chain....a loop! Dreadful to find that by the roadside at night!!
regards
Andy

 

[Nealh]

Go with the original set up as the rear frame stay length may be longer .
The correct length using Shimano's guide is to wrap chain around the front and rear largest chain ring /gear and then add two extra links where the chain links meet, once this is done fit the chain as normal through the derailleur.

 

[onthe-edge]

Go with the original set up as the rear frame stay length may be longer .
The correct length using Shimano's guide is to wrap chain around the front and rear largest chain ring /gear and then add two extra links where the chain links meet, once this is done fit the chain as normal through the derailleur.

hi Nealh, I never once considered the length of the chain stay but now you point it out that would easily explain the need for different chain lengths, many thanks

 

[Tarka]

For what its worth, I have a 7 speed, 20" Frame and the chain length is 54" pin to pin. I use a quick link and so far have no problems with the added strain of a Bafang mid drive.

There are many guides on-line of how the gear train should look in either low or high gear.

 

[Nealh]

You need to be guided by what I have mentioned in #8 or the manufacturer as bike stays/frame length may vary, bikes with the battery behind the seat post for instance are long wheel based and chain will be much longer. If you don't use the simple large chain ring to largest gear wrap method then you risk snapping the chain, mashing the gear teeth and derailleur damage as well as not being able to have the lowest gear.
Sram recommend only one extra link.

 

[Deleted member 25121]

An excellent video with accompanying written description on how to correctly size chains from Park Tools:

Chain Length Sizing

This repair help article will take you step by step through the different methods of sizing a bike chain for your drivetrain.

www.parktool.com

In my experience they make exceptionally good tools and their repair book is very well written and informative:

Park Tool Big Blue Book of Bicycle Repairs Volume 4: Amazon.co.uk: Welcome

Shop Park Tool Big Blue Book of Bicycle Repairs Volume 4. Free delivery and returns on all eligible orders.

www.amazon.co.uk

 

[sjpt]

Sram recommend only one extra link.

Surely, one pair of links?

 

[ishitha5]

Nice Video with great description.

 

[onthe-edge]

Thanks to everyone for your advice, I changed the bottom bracket today (that's another saga) and put the crank back with a new chain.
I watched a couple of youtube vids first and I'm pretty sure everything is OK. even with the shorter chain. It seems the chain has more tension now but it's not too tight as there is still a bit of wiggle room for the derailleur ,and it runs through the gear shifting nicely.

 

[soundwave]

the chain is to short you can rip the mech in half extended that far in top gear.

 

[RoadieRoger]

I had the same problem with my Batribike 20 in. Folder . The longest chain to suit 6,7 and 8 speed set ups was 118 links which was 4 shorter than the original . This resulted in the chain coming off the sprockets a few times . I ordered another 118 Link chain and some spare links and made up a chain to the original size . No problem since .

 

[onthe-edge]

Thanks fellas, I have another new chain for 7speed that's even shorter, so I'll use a piece of that as an extension.

P.S. I came across a convoluted formula for working out the length......
in my case
chain-stay length x 2 = 36.5
+ number of teeth on the chain ring divided by 4 = 11.5
+ number of teeth on largest cog divided by 4 = 8.5
add 1 = 1.0
chain length total = 57.5 ins.