I’ve been mooching around on an old Cotic Roadrat singlespeed, but decided I need some gears for riding up hills. I have bought deore 10sp shifter, rear derailleur, and 11-46 cassette. The derailleur says it’ll work up to 46t. Got it all on to the bike fine.

I bought a new chain, which I’ve sized according to a couple of vids (big cog to front, the ends meet at a reference link, add two).

I can manually shift the chain on to the largest cog without the cable tight. It’s close but it goes. I’ve got the b screw fully tightened, high and low adjust seem fine. There is not much room between the chain stay and the mech though.

When I tighten the cable, it’ll shift cleanly up to 7th/8th or thsreabouts, but then it jams against the cassette.

Is this down to trial and error readjustment, or is there something else I need to consider? I have seen advice suggesting the chain’s too tight, or too loose. I’ve got horizontal dropouts so I’ve moved it round a bit. I haven’t seen any advice on chairing, is 46t at the front too big if the chain fits. Is there something else there I need to look at?

Thanks for any ideas.

What’s the model number if the rear derailleur? The last time I looked deore maxed out at 42 I think.

You can add a goat link copy for a couple of quid. That helps a bit. Unfortunately it’s a bit late now but you are better off with an 11 speed mech. Works with the 10 speed shifter and cassette plays nicely with bigger gears. There’s also the old bodge of screwing the b screw in from the wrong side to get a bit more b tension

It’s a RD-M5120-SGS. Says on the box it’ll go 1×46 or 2×42. Would a smaller front chain ring make any difference?

I did wonder about a goat link, might give that a go.

Hmmm.

It should work, I have the same setup. The front ring won’t make a difference as a single chainring makes no change to chain slack. Chain length should be big-big plus two links(not going through the mech). I don’t think I got near the limit of the b limit screw which suggests that your mech hanger might be in the wrong place in relation to the cassette.

I wonder if your roadrat chainset is middle and big ring instead of middle and granny like a mountain bike.

Might make the chain line a bit too far to shift properly. Just a thought 🤔

Deore chains aren’t directional are they? Like the road 11 speed are?

<img src=”

” alt=”this (if it works) ” /> is what it looks like.

Chain has the writing on the outside, which should be OK.

@didnthurt it’s only one ring, and it looks pretty central in relation to the cassette. I can see it pulls outward to the highest gear about the same amount it pulls inwards to the lowest gear, if that makes sense.

EDIT: phew, photos worked, shame they’re not very useful 🙂

I think the solution is to stop mooching about and go full beans, it’s the only way on SS 🙂

More B or a goat link style extender required there

I’ll try those, ta. Not the full beans bit though. It’s too hilly and my knees are too feeble!

Shouldn’t the b link point horizontally backwards rather than straight down?

Dc1988 has it. Where the mech bolts to the frame there’s a tab on the mech and one on the hanger. The tab on the mech should be behind the one on the frame not in front of it. Sort that out first then when the mech is in the second biggest cog, alter the B screw so there is a chain thickness’ gap between the teeth on the jockey and the biggest cog.

That would need an extender then I reckon. I can see the tabs you describe, but there’s no space for the mech out the back at the angle the existing hanger tab seems to require.

There’s definitely room there, just give it a try. Backing off your B screw will give you a bit more play. While you’re at it, the chain is on the wrong side of the tab between the jockey wheels, you might want to sort that too.

Yes! That did it. The mech is hanging at a different angle, and all looks good. I’ll deal with the chain too, good spot.

Thank you all, much appreciated!