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Chain length for double crank?

915 views 18 replies 7 participants last post by  AndrwSwitch 
#1 ·
I had a 36/22 and replaced the 36t with a 32t, but can't find online how to measure the correct chain length on a double.

On my other bike, I replaced the outside with a bash guard and figured I'd shorten the chain when I replaced it, but when I did the big big measurement, the chain would get jammed on the cassette when shifting multiple gears at once and I had to lengthen it a few links, so that didn't work lol.. So what's the correct procedure to measure the chain length on a double?

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#12 ·
While a longer cage is not as sensitive to a too long chain as medium and short ones, it's advisable to disregard cage length entirely when figuring out the proper chain length.

It's "chain around the biggest front and rear, + 2 links".

Doesn't matter how many cogs or chainrings you have, doesn't matter which derailleur you have, doesn't matter what size things are front and rear... Don't make it too difficult.
 
#7 ·
On road bikes, it's the same. I'm surprised it gave you trouble on your other bike. I'd look for some other cause. Maybe having a little more tension due to a shorter chain was making your rear derailleur do something weird?
 
#8 ·
Derailleur was new and adjusted fine.. Added an extra 2 links I think and its fine. I could shift one by one, but shifting 3 gears at a time and it got jammed and didn't shift.

I'm going to shorten my chain by a link to compensate for the smaller chainring.. I'll see how it measures first and go from there.

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#11 ·
Since you still have the long cage rear derailleur, if you wanted to be conservative you could just remove one link and call it a day. You could remove none and everything should be okay too. I'm not sure if chain slap is an issue on fat bikes...
 
#14 ·
I think you may have that wrong, I'm pretty sure 1 link is 1/2 inch and 1 inner+1 outer link=1 inch (2 links).

Maybe I'm the one who has it backwards though, during my entire career working on bikes I had never heard of, nor used the "big/big plus 2" method and only found out about it here on mtbr after retiring from that work.
 
#16 ·
#17 ·
I'm pretty familiar with half links from working on old beaters "back in the day"

Maybe I'm just misunderstanding your meaning but I do know that a 114 link chain has 114 pins @ 1/2' each. According to Park 2 links is one set of inner and one set of outer plates- Park Tool Co. » ParkTool Blog » Chain Length Sizing

Also Sram- https://www.sram.com/sites/default/files/techdocs/my10-sram-tech-manual-rev-a.pdf

So two links = one inch, right?
no.. but yes.. again depends on manufacturer these days ... a "true link" is one inch.. but even like you've pointed out.. they state 116/114/112 links chain length which is plate count...

but the original chain length theory of Large-Large +2 links should be Large - Large + 2 inches or 4 plate sets... again.. it's kinda gone by the wayside as the manufacturers have done away with it over the years to avoid issues/confusion and derailleurs are over sized to compensate as they will often do a good bit more chain take up then they are rated at.

again.. toooo long is better than tooooo short ;)
 
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