Chainline woes!

Ben6899

Manc33 wrote:

The #1 thing to remember is that small-small will write off the rear mech. :!: So accidental shifts are a no-no.

How so?

Manc33

Ben6899 wrote:

Manc33 wrote:

The #1 thing to remember is that small-small will write off the rear mech. :!: So accidental shifts are a no-no.

How so?

In small>small the rear mech ends up all folded up and it sounds awful. With the bike upside down in this gear, you can't even turn the pedals to change out of the gear and have to open out the rear mech swingarm, whilst shifting the gear lever, whilst turning the pedals. Who knows what hard pedaling in that gear would do to it, rip it apart probably.

52t large chainring and 32t low sprocket. Chain is 57 links. The upside is big>big works and won't rip anything apart (albeit it being on the limit).

Ran a chain 3 links shorter and the rear mech just looked absurd in middle>32t.

Ben6899

Chain is too long or the mech doesn't provide enough "wrap" for your chainring/cassette combination.

darkhairedlord

On any properly set-up bike with compatible components then small-small or large-large should not really be a problem. For your bike you should just be thankful you can pedal in the super low gear you have built it around and start getting up those hills you have been dreaming about.

Ouija

Chains should be cut for the gears you actually use, not for hypothetical ones you don't (one of the main problems with online chain length calculators). You shouldn't be using big/big on a triple as this will mean a lot of cross chaining and seriously mess up your chain and cassette. Should never get more than two thirds of the way up the cassette on the big chainring so that is the combo you should cut the chain for so that the derailleur looks right. This will stop the rear derailleur folding up on the small/small combination.

Not that you should use small/small either. In fact, on a triple, if your front mech is set up correctly you shouldn't even be able to get small/small or big/big without massive chainrub on the mech at least two cassette rings before reaching either combination (and on some chainlines even middle/11t should generate a bit of rub on the outside fo the front derailleur). You have to remember that the granny ring on a triple sits closer to the frame than the smaller ring of a double and that the big ring sits further out from the frame than a big ring on a double, so chains have to bend a lot more to reach the opposite extremes of the cassette (the more centrally mounted rings on a double allow you to go further up and down the cassette before rub).

Manc33

I had it working with a MTB shifter (no trim) but you need the cable pretty loose. Still it does work and the spacing is fine, doesn't rub in lowest gear or middle>32t. Or I can use a flat bar shifter that works but the shift is miles stiffer than a XT/XTR front shifter and it has that stupid trim thing on I can't stand.

Having it that way without a trim meant giving it a big shove to change from granny to middle but I can live with it.

Maybe the R770 left shifter works better than the R440 does, I will have to look out for just a left one of the R770 but being a flat bar shifter it will have that trim function on it I don't like. It actually rubs more with the trim function because changing from large to middle chainring you have to "untrim" it every time. :roll:

Ouija

Trim is very uncommon with flat bar shifters. Only ones i've owned are a set of 8 speed Shimano ST-R244 all in ones with selectable V-Brake/Caliper pull ratios and the trim between the granny ring and middle. Essentially one click to go from middle to granny but a two click push from granny to middle (though the distance pushed is the same as from middle to outer... the trim being achieved by pushing only half the regular distance).

Ben6899

On a properly set up bike, ALL chainring/cassette combinations are accessible without straining the chain/mech or having too much slop at the other extreme.

There will be chain rub on most of these correctly set up bikes and I certainly wouldn't recommend using big/big, big/big-1, small/small or small/small+1. But you can't be riding around worrying about shifting into a gear combination that will tear the mech off the frame...

Manc33

Its just a drawback of having such a big gear range.

Small-Small works on most setups, but not when it has a 24t granny, 52t outer and a 11-32t cassette.

I would only use the lowest three sprockets on the granny ring anyway because middle>lowest overlaps. The granny ring just provides three "super low" gears.

Middle > 32t (1st sprocket) = 1.19 turns
Granny > 21t (4th sprocket) = 1.14 turns

After the 21t I have three bigger sprockets (24-28-32), the granny ring would only be used with these, all the smaller sprockets overlap with the middle chainring. What I might do as I get fitter is put that 12-23t on I used to use on my MTB. I suppose then you're getting a lot more usage from all three chainrings with them being spread apart so much, you're also solving the chain length issues. I would need a short cage rear mech then though.

Its more of a bonking ring than a granny ring. :P

darkhairedlord

Manc33 wrote:

Its just a drawback of having such a big gear range.

Small-Small works on most setups, but not when it has a 24t granny, 52t outer and a 11-32t cassette.

I would only use the lowest three sprockets on the granny ring anyway because middle>lowest overlaps. The granny ring just provides three "super low" gears.

Middle > 32t (1st sprocket) = 1.19 turns
Granny > 21t (4th sprocket) = 1.14 turns

After the 21t I have three bigger sprockets (24-28-32), the granny ring would only be used with these, all the smaller sprockets overlap with the middle chainring.

Its more of a bonking ring than a granny ring. :P