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Shimano Tiagra - Expanding Cassette??

by Walshinoz
Thu, May 20, 2021 14:38
9

Hi,

I have a 10 year old roadbike that is kitted out with a Shimano Tiagra groupset. It is 50/34 on the chainwheel and 11/28 (10spd) on the cassette. It is in pretty good nick but  don't really want to spend lots of money upgrading ( I would rather put that towards a new one when the time comes). I have a trip coming up with a few tasty gradients over a few days. So question: Is there any way I can expand the rear cassette to incorporate a bigger granny cog, say a 32t (or a 30t), without having to buy a new groupset / lots of new parts? Is there something similar to the 'oneup' system where I can take one sprocket out of the current cassette and replace with a 32t sprocket in the cassette? Or can I replace with an 11/32 cassette only (if I can get one) withut buying a new shifter/derailluer/chain etc? I understand the issue with the cage length, but if I only used a new 32t sprocket whilst in the 34 chainwheel upfront (and adjusted tbe B screw) would that work? Or am I just barking up the wrong tree?? Just trying not to spend a lot of money.

Many thanks in advance

Cheers, Jason

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9 comments

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Walshinoz | 3 years ago
1 like

Many thanks all, appreciate the feedback. At least it looks like there is a way that doesn't involve a full refit! I will follow up the below suggestions, which hopefully saves me from walking up the steeper climbs!!

Great responses, cheers

Avatar
tincaman | 3 years ago
1 like

You could fit a cheap hanger extender like this:

https://www.ebay.co.uk/itm/143965962587

 

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Dnnnnnn | 3 years ago
1 like

If you really want to save money and can get hold of an old cassette with a 30t or 32t sprocket then you can knock out the three long rivets that hold the sprockets together and swap it for a sprocket in your current cassette (having also knocked out its rivets). A proper hole punch helps for this task.

Given it's the last sprocket on the block it doesn't even need to come from a 10spd cassette - a 8 or 9 speed sprocket will work fine (they're only about 0.2mm thicker).

If your freehub body is soft aluminium, rather than steel (unlikely but not impossible) then it might be worth re-using the rivets - they won't hold the sprockets totether anymore  but they will prevent individual sprockets biting into the aluminium by spreading the load across the cassette. Insert from the rivets from the small sprocket end of the cassette so they don't fall out.

I agree with other posters that your existing rear mech should work OK, even if it's a short cage - and that you need to check your chain is long enough!

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wtjs | 3 years ago
3 likes

This is off-topic and no help to the OP, but I feel obliged to note again that crappy Sora 9-speed is really good and trouble free, with clean shifts.

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Grahamd | 3 years ago
1 like

I replaced my Tiagra rear derailleur with a long cage 10 speed Ultegra, handles 34 cassette without needing to adjust B screw at all. 
Agree with John Stevenson, that 4700 RD is not compatible.

Do factor in that a new chain will likely be required, unless you have some spare links.

 

Avatar
Walshinoz | 3 years ago
1 like

That's great feedback, thanks all for the comments. Its good to know there are options that seem like they will work. Really appreciate taking your time to respond, I will certainly follwo up the below options.

Cheers all!

Avatar
OnYerBike | 3 years ago
1 like

As Rich says, giving it a go is the best bet to begin with. The "official" capacity is very conservative so it might work even if it shouldn't. I would however be inclined to put on a new chain. Firstly I wouldn't want to risk accidentally changing into the wrong gear a causing major problems, and secondly a new cassette will work better and last longer with a new chain.

If it's not happy, you should be able to get away with just replacing the derailleur if you can find the right one. I think you would be looking for the long cage Tiagra 4600 derailleur (RD-4601-GS). Note that, as I understand it, the new Tiagra series (4700) would not be compatible.

Failing that, I think all current and recent (mechanical) 11 speed derailleurs have the same cable pull ratio as the old Tiagra shifters (not the new Tiagra ones though!) so you could put an 11-speed 105 (or Ultegra etc.) derailleur on and it should work. I've got a 105 derailleur on my otherwise Tiagra bike for this exact reason and it works fine (NB - bought because of price/availability, not because I thought the performance would be noticeably different).

Avatar
wycombewheeler replied to OnYerBike | 3 years ago
2 likes

OnYerBike wrote:

 Firstly I wouldn't want to risk accidentally changing into the wrong gear a causing major problems,

't shift

does it cause major problems?

Once i twisted a chain took some links out and reconnected with a split link, reminded myself not to use big/big and carried on, 40 miles later I forgot and tried to shift. I found it just wouldn't shift, but nothing broke.

I think you'd have to be putting a lot of power down at high revs to damage anything

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Rich_cb | 3 years ago
1 like

Your best bet is to buy an 11-32, screw the B screw all the way in and see if it works.

I used to have a bike with Tiagra 4600, short cage and I'm sure I got an 11-32 to work in that way.

If it doesn't work a cheap derailleur hanger extender should do the trick.

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