Struggling to index since changing from a 12-30 to 11-21

ollie.tansley

Hi all

I recently changed the cassette on my Tiagra based bike from an 12-30 Shimano CS-4600 to a Miche Primato 11-21. Ever since making the change I'm having difficulty getting it to index properly.

I can't get it to work at all really in the big ring, if I get it so it goes down the cassette OK then it won't go back into the biggest cog at the back - if I go the other way then it won't change properly. I can get it sort of OK in the small ring, much better than the big ring but it is still a bit hesitant going up the cassette towards the biggest cog whatever I do really.

I resized the chain (smaller) when I changed it by following a Park Tool guide and cross checking against various others so hopefully the chain is the right length. The one thing I've spotted is that the top jockey wheel is much further from the cassette than it is supposed to be from what I've read, it is more like 30mm rather than 6mm. I've completely removed the b tension screw and it doesn't come any closed (see attached pics).

Is the jocket wheel/cassette gap likely to be the problem? If so, what do I need to change? I thought I might need a different rear derailleur but I've been unable to track down what exactly I need to change.

Many thanks!

Ollie

whyamihere

The chain is too short, and the b gap is too big, you're never going to get decent shifting like that. You'd be far better off with a larger cassette, something like an 11-25 would significantly reduce the b gap while not increasing the gaps too much. A different mech might be better able to cope as well. Tiagra mechs specify a 25t as the minimum low sprocket, but a different mech will likely cost more than a new cassette.

If you want to stick with that cassette, adding a link to the chain would help a bit, but it's never going to be perfect.

arlowood

Another thought is what hub type is on your wheelset - is it a hub that can accept up to 11-speed cassettes? If so then your 12-30 Tiagra cassette would only need to be fitted with a 1.85mm spacer. However other brand cassettes may need an additional 1mm spacer to get them to line up accurately on the hub.

Not exactly sure what the Miche requirements are but it might be worth investigating as another source of your indexing issues

ollie.tansley

Thanks a lot for the response. I actually ordered another 1mm spacer at the same time as the cassette as I read on Sheldon Brown that I might need one but I couldn't see that I'd be able to fit the cassette on with a spacer. I think I have the Hyperglide-C type body as the splines don't go all the way to the edge - that is the one that doesn't need a spacer isn't it?

ollie.tansley

whyamihere said:

The chain is too short, and the b gap is too big, you're never going to get decent shifting like that.

OK thanks a lot, I got an 11-21 because I wanted a very close ratio cassette due to using this bike on a dumb trainer and wanting to be able to vary my cadence by a few RPM. I found with an 12-30 that the jumps between cogs were way too high and I could go up or down by 10 RPM at a time. I will take a look at the 11-25 although I suspect the jumps will be too big.

I'll also look to increase the length of the chain again, is one link literally an inner link (or outer link depending on end) or an inner and outer link?

On a different mech, I'm not too bothered about it costing more than a cassette - it is the close ratio I'm most interested in. What sort of mech would I need to get to get better shifting?

ollie.tansley

Also just for my own info in the future, what did you look at to know the chain is too short please? Just so I don't mess it up again

whyamihere

You need to add both an outer link and an inner link, there's no way of adding just one or the other.

Ultegra 6700 has a minimum low sprocket of 23t, so if you could find one of those it would work better with the 11-21, but would definitely work well with an 11-23, which gives smaller gaps than the 11-25. Dura Ace may be better still, but I haven't found a reference for this yet.

ugo.santalucia

Chain is too short and jockey wheels are too far from the sprocket. The latter is easily sorted by undoing the B screw.

masjer

If the top pic is in the big chainring -biggest rear cog, then the chain might be the correct length as you'd never ride with that selection (cross chaining). With the correct gear selection the upper jockey wheel will also be closer to the cassette- not ideal but should work ok- especially as a turbo bike.
Try new inner/outer cables if they're old/worn.

dj58

Is it a 10sp or 11sp freehub, 4600 or 4700 RD As already pointed out you are out of the range for the min. low sprocket so I doubt you will get it to work satisfactorily. CS-4600 cassette has a built in spacer so non needed on a 10sp freehub though a 1.85 mm is required for an 11sp freehub. I don't non the requirements for the Miche cassette.

https://www.sjscycles.co.uk/cassettes/1123-shimano-ultegra-cs6700-10-speed-cassette/