lyle.coop

I'm making the switch to an 11-51 rear cassette and long cage derailleur. Any tips on properly sizing new the chain? I'm worried about chain growth when the suspension cycles.

Thanks

cxwrench

Yeah, follow the Shimano instructions:

Mtb chain sizing

lyle.coop

Thanks. To check the full compression of the shock should I just take all the air out OR remove the rear shock?

cxwrench

Read the instructions again. And this is a mechanical question and should be posted in 'bicycle mechanics' not here.
* For full suspension bikes, check the length of the chain with the suspension in its fully extended position.

SRAM wants the suspension compressed fully.

Kapusta

The idea is to check the chain at the point in the suspension travel where the chain length will be longest. On most newer bikes this will be when fully compressed. But it can’t hurt to check throughout the travel.

You can let the air out of the shock, or just disconnect it from one end.

cyclezen

I would
subtract the teeth number of the largest cog of older (smaller ?) cassette from the largest new cog (the 11-50?) assuming the old cassette smallest cog is within 1 tooth of the new cassette (11/12?)
if the older largest cog is 42, new is 50 gives 8 teeth - every 2 teeth equals one chain link pair. so 4 more link pairs
If there's an appreciable difference in the jockey cage from old to new - measure from jockey pivot to lower jockey wheel axle , 1 inch = chain link pair.
42 cassette to 50 cassette = 4 link pairs
jockey cage is about 1 inch longer ??? 1 link pair
TTL = 5 link pairs - longer than the prior chain

Ride on
Yuri
Edit: if there's also a change in the chainrings, then you would again compare 'Large' to Large chainrings, or Large Double(triple) to whatever a 1x size used...
same math 2 teeth = 1 link pair

cxwrench

Why on earth would you think this hard if you don't even know if the old chain was sized correctly? Why not just install the new according the drivetrain manufacturer's directions and know it's right?

cyclezen

Hard? a few seconds of thought (back when a friend asked me...) as opposed to scouting down what was the original 'stock' chain length ??? and then still having to apply some process to deciding a new length for gearing changes?
... if the old chain worked fine, with the bike's suspension... so will the new chain using the method I suggest.

I'm assuming you read and know by heart the shimano directions... ?
some of which = "Full suspension bikes * For full suspension bikes, check the length of the chain with the suspension in its fully extended position."
and "• For full suspension bikes, length [a] will vary according to the movement of the rear suspension. After shifting to the largest chainring and the largest sprocket, make sure that the chain length is not too short when dimension [a] is at its maximum extension. If the chain length is too short, drivetrain components may be damaged due to excessive load on the drivetrain."
and "Full suspension bikes 5 to 6 links + a QUICK-LINK 6 to 7 links + a connecting pin".
And you gotta see the wonderfully clear illustrations...
LOL!
if one decides and cuts the length too short ? add how many links back on? and how reliable are 'added' links?
LOL!
LOL!

alexdi

Put the chain on the bike with the suspension unloaded and size it so it has just enough tension to keep clear of the upper derailleur pulley when you're in the smallest sprocket. No need to count links.