Cassette replacement

[mattsccm]

You can push a SS to 32t with the right frame. Cannondale CX frames for example. I wouldn't worry about 30t.

[Pebble]

I take it the tell tale sign that a derailleur has past its low gear limit (biggest cog) in that the B scew has reach itsd limit and there is still viabration between the cog and the guide jockey?

Is it possible to use a longer b screw ?

[mattsccm]

Yes or put it in from the other side.

[iandusud]

You can push a SS to 32t with the right frame. Cannondale CX frames for example. I wouldn't worry about 30t.

I was tempted to say the same as I run a 32 with an ss ultegra rear mech on one of my bikes (Giant). However it does take very careful setting up and correct chain length is critical, and as the OP clearly stated his lack of experience with setting up gears I though it wise not to suggest a setup outside of the manufacturers specs.

[Brucey]

it is perhaps worth mentioning that shimano don't always mean the same thing when they give specifications and capacities for derailleur systems. There are (IME) two limiting cases;

a) where the recommended 'maximum capacities' represent what will work on nearly every bike, but outside of that there is increasing risk and/or compromise.

b) where shimano don't make alternatives in that groupset, so they say 'x' is a limit whether it is or it isn't.

For example if shimano only make chainsets with a 16T interval in a given groupset, they are quite likely to claim that the maximum front interval is 16T whether it is or it isn't.

If compatible cassettes are available with larger sprockets (as is the case here) you can assume that it is a) that applies in the case of an SS mech. So that isn't to say that you can't push the capacities of the mech (both in largest sprocket and overall capacity), just that there is increasing risk and compromise in its function.

So if you want an easy life, stick to the recommended specifications. However if you are prepared to experiment, and/or accept risk/compromise, then experimentation is fair game.

Some of the risks are obvious, some are subtle; for example it is fairly obvious to most folk that it is a good idea if you can at least select big-big without breaking anything, even if you don't plan to actually use that gear. However what is less obvious is that if this shift will only just go, there is another risk; there is no capacity to spare, so if you try and do a (slightly bizarre) double-shift then you can still end up in a transmission-busting scenario anyway.

cheers

[Glyno]

I am so grateful for the really helpful and informative replies - thank you very much!

I'm now just to decide between 28T or 30T and wonder whether there'd be a noticable difference in shifting due to the slightly bigger jump with the 30T.
I'm not even entirely sure if my RD is short or medium cage (though this may not be an issue), all that's stamped on it is: RD5800 with no reference to ss or gs. I've attached a couple of (poor) photos, maybe someone could identify the size?

I promise not to pester any more for a few days, at least.

Thanks again

[Brucey]

the links in this post show both types SS and GS. I think you have SS

FWIW shimano say that maximum sprocket sizes for 5800 series RDs are

32T for RD-5800-GS

https://bike.shimano.com/en-EU/product/component/105-5800/RD-5800-GS.html

and

28T for RD-5800-SS

https://bike.shimano.com/en-EU/product/component/105-5800/RD-5800-SS.html

in practice unless your frame has an unusually short gear hanger you can usually 'push' an SS mech to 30T without insurmountable difficulties.

cheers

[Glyno]

the links in this post show both types SS and GS. I think you have SS

Yes, I studied the pictures in the links but was still unsure.
30T would be my maximum anyway, so things should be fine, thanks again.

I think this picture pretty much confirms that I have the ss RD...

[cyclop]

You'd definitely notice the difference between a 25t and 28t on the hills. I certainly would

Rightio, I won't be going down from 28 then. Is 30T a good choice, or would I be considered a bit of a wimp?

I,ve gone from 52,then 50,then 48 ,now42 tooth big ring,am I bovered?I,m 68 and can still ride the steepest hill in Britain(Harlech) but can,t cycle fast enough to stay with my local group,still not bovered.P.S,my lowest gear was 26 front,34back,my climb anything in any state of exhaustion gear.

[iandusud]

I'm now just to decide between 28T or 30T and wonder whether there'd be a noticable difference in shifting due to the slightly bigger jump with the 30T.
Thanks again

That looks like an SS to me but I wouldn't hesitate about going for a 30t in your shoes. (Although it might make walking uncomfortable - just thought I'd add that before smart Alec ).