Chain length issue

[AlanW]

I'd be interested if the OP has encountered any issues with the chain length and being able all of the possible gear ratios by fitting a smaller chain ring?
(Mod Note: post moved from another thread)
l have recently fitted a sub compact 30/46 chainset, coupled with a 11 speed 11/34 cassette.

I appreciate that cross chaining isn't really advisable to do, but sometimes it's done.

With the current cassette (11/32) l can utilize every possible gear option. However, I've just fitted a 11/34 cassette and when its on the 30 at the front and the 11 on the cassette the chain is far to slack, but the 46/34 combo works fine. So the mech clearly has the range to be able to do it.

I removed one chain link and now the only gear ratio not possible to use is the 46 on the front and 34 at the rear as the chain is now simply not long enough to accommodate it.

In truth it's not really a problem as it's a less than ideal chain line. My only issue is that if l do go to select that ratio by accident it will probably either snap the chain or worse case, rip the mech off the hanger.

I've looked at maybe fitting a rear mech extension, but l dont think that's the answer as l don't have an issue with the clearance between the jockey wheels and the largest sprocket on the cassette.

Any thoughts?

 

[Ajax Bay]

30/46 chainset, . . . just fitted a 11/34 cassette and when its on the 30 at the front and the 11 on the cassette the chain is far to slack, but the 46/34 combo works fine. So the mech clearly has the range to be able to do it.

I removed one chain link and now the only gear ratio not possible to use is the 46 on the front and 34 at the rear as the chain is now simply not long enough to accommodate it.

In truth it's not really a problem as it's a less than ideal chain line. My only issue is that if l do go to select that ratio by accident it will probably either snap the chain or worse case, rip the mech off the hanger.

As you say (but without the caveat) there is an existential risk with a chain too short to go large/large. People say 'but I never cross chain and use that'. But sooner or later, probably in stress and with force applied after a high speed downhill and swoop across a bridge followed by a cheeky turn up, it'll happen and there will likely be sadness.
On the other hand, when the chain (long enough for large/large) is on 30t ring and 11t sprocket, assuming a GS cage not an SS, the return stretch of the chain may interfere with the chain links around the tension pulley, but no damage will occur. The noise thus created will remind the rider that they need to shift to the large chain ring pronto (and probably a double shift hopping up to the 13t sprocket at the same time).
Or adapting the esteemed Chris Juden's words - see the link shared by @roubaixtuesday https://forum.cyclinguk.org/viewtopic.php?t=153478&start=45 :
"the chain grating against [itself] is a handy reminder to shift up a ring and down two or three sprockets, for a similar ratio that runs nice and smooth!"
I have a perfectly standard 105 RD (GS) and need a capacity of up to 39. My chain tells me once I carelessly go 30t-12t, and I shift.

 

[ColinJ]

As you say (but without the caveat) there is an existential risk with a chain too short to go large/large. People say 'but I never cross chain and use that'. But sooner or later, probably in stress and with force applied after a high speed downhill and swoop across a bridge followed by a cheeky turn up, it'll happen and there will likely be sadness.

I was discussing this with @GuyBoden on a ride last week. He had fitted a 46 tooth mega-sprocket to his bike and commented that he had to be careful not to select big-big. I told him that I wouldn't trust myself not to do that so I had made sure that my bike worked in all gears when I fitted a triple chainset and a bigger cassette to it. As if to prove my point, I accidentally selected big-big at least twice after that!

 

[GuyBoden]

I was discussing this with @GuyBoden on a ride last week. He had fitted a 46 tooth mega-sprocket to his bike and commented that he had to be careful not to select big-big. I told him that I wouldn't trust myself not to do that so I had made sure that my bike worked in all gears when I fitted a triple chainset and a bigger cassette to it. As if to prove my point, I accidentally selected big-big at least twice after that!

@ColinJ on your very steep Calderdale hilly ride (over 20%) I used that 46t rear sprocket to make climbing easier, but I was very careful not to use the big 48t front ring on my triple. I was thinking in future for your steep rides, just to be safe, I'd temporarily adjust the front derailleur screws, so it wasn't able to select the big chainring. I'm back to using a normal sized rear sprocket for my Cheshire rides, although Swiss Hill (17%) was difficult the other day due to the cobbles, so I used a 40t rear sprocket, which is fine in big-big.

 

[ColinJ]

@ColinJ on your very steep Calderdale hilly ride (over 20%) I used that 46t rear sprocket to make climbing easier, but I was very careful not to use the big 48t front ring on my triple. I was thinking in future for your steep rides, just to be safe, I'd temporarily adjust the front derailleur screws, so it wasn't able to select the big chainring. I'm back to using a normal sized rear sprocket for my Cheshire rides, although Swiss Hill (17%) was difficult the other day due to the cobbles, so I used a 40t rear sprocket, which is fine in big-big.

That makes sense; we didn't really ride fast enough to need that 48 ring.

 

[Ajax Bay]

very steep Calderdale hilly ride (over 20%) I used that 46t rear sprocket to make climbing easier, but I was very careful not to use the big 48t front ring on my triple.

What rear derailleur can wrap enough chain for a 48-38-28 chainset and a 12-46 cassette?

 

[Tigerbiten]

What rear derailleur can wrap enough chain for a 48-38-28 chainset and a 12-46 cassette?

None.
You set it up with the minimum chain length such that big-big works safely.
This means you can use all sprockets with both the big and middle chainring.
The small chainring is more iffy as you'll have to much chain wrap in the smallest 3-4 sprockets.
So you just don't use these combo's.
I've had a recumbent trike setup such that I couldn't use the smallest 2 sprockets when on the smallest chainring due to excessive chain wrap, 48/36/22 and 9-32.

 

[Ajax Bay]

A 9t sprocket in a cassette? Linky?
Anyway Guy needs a wrap capacity of 54 teeth. You 'only' needed 47.
I appreciate that the work around is to let the chain tell you when it won't wrap anymore: see my post ^^^.

 

[roubaixtuesday]

What rear derailleur can wrap enough chain for a 48-38-28 chainset and a 12-46 cassette?

That's a capacity of what, 54?

I run Sora on 46-36-24 with 11-36 which is 45 and slightly outside the nominal capacity of 43

If you changed the front to 44 - 34 - 24 and 11-40, capacity 49, I bet it would be usable with the small/small lacking tension.

24/40 is a slightly lower gear than 28/46

 

[GuyBoden]

None.
You set it up with the minimum chain length such that big-big works safely.
This means you can use all sprockets with both the big and middle chainring.
The small chainring is more iffy as you'll have to much chain wrap in the smallest 3-4 sprockets.
So you just don't use these combo's.
I've had a recumbent trike setup such that I couldn't use the smallest 2 sprockets when on the smallest chainring due to excessive chain wrap, 48/36/22 and 9-32.

Yes, that's my usual setup, but I used a 46t cassette just for Colin's steep Calderdale ride, but obviously I didn't use the big front chainring.

 

[Tigerbiten]

A 9t sprocket in a cassette? Linky?

A customised 9-26 9 speed Capreo cassette, a cassette for small back wheels.

 

[AlanW]

I'm wondering if fitting a GRX810 rear mech would solve the issue?

It's compatible with Ultrgra shifters, and has a max sprocket rating at 34T

 

[roubaixtuesday]

I'm wondering if fitting a GRX810 rear mech would solve the issue?

It's compatible with Ultrgra shifters, and has a max sprocket rating at 34T

GRX810 Total capacity is quoted as 40T.

https://bike.shimano.com/en-EU/product/component/grx-11-speed/RD-RX810.html

Your setup is 30/46 11-34.

You need capacity of (46-30) + (34-11) = 39 for your setup to work.

Ultegra r8000 is quoted as 39T capacity.

https://bike.shimano.com/en-EU/product/component/ultegra-r8000/RD-R8000-GS.html

What "issue" are you trying to solve?

 

[Ian H]

You simply need a derailleur with a longer cage. Otherwise you put up with not being able to get every gear.

 

[AlanW]

GRX810 Total capacity is quoted as 40T.

https://bike.shimano.com/en-EU/product/component/grx-11-speed/RD-RX810.html

Your setup is 30/46 11-34.

You need capacity of (46-30) + (34-11) = 39 for your setup to work.

Ultegra r8000 is quoted as 39T capacity.

https://bike.shimano.com/en-EU/product/component/ultegra-r8000/RD-R8000-GS.html

What "issue" are you trying to solve?

The ability to be able to use all gear ratios, full explanation in the very first post on this thread.