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My wife has a worn 9 speed 12-27 cassette and worn chain, so when replacing I would like to use a cassette with a 30T if possible so was looking for advice on cassette and Derailleur replacement.
Currently I think she has a Tiagra RD-4400 derailleur which has a max rear sprocket of 27T with 105 9-speed shifters and a 52-30 chain-ring.

So I was looking at HG50-9 11-30 cassette which would make capacity (30-11) + (52-30) = 41T.
I found Shimano 105 5701 10 Speed Rear derailleur which can take 30T on back, but capacity is 40T, so is there flex in capacity for extra 1 tooth of 41T.
I did look for a 12-30 as she doesn't need the 11T sprocket and this would make capacity 40T, but could only find IRD 12-30 cassette which is £75 compared to £20 for Shimano 11-30.

Are then any downsides to changing cassette - would there be much difference in how smooth gear changes are having a wider gear range, or because Shimano 105 5701 is both newer (I think Tiagra RD-4400 is 10-20 year old technology) and 105 is above Tiagra, would it actually be smoother?

Any advice/comments appreciated.

Mike

14 comments

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DaveE128 [885 posts] 2 months ago
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So, easy questions first:

Downsides to moving to a wider range cassette:

  • bigger steps between gears mean you need to be able to ride with a slightly broader range of cadences.
  • slightly less quick/smooth shifting, but it will still be perfectly acceptable unless you're really fussy.

I believe the 105 5701 rear mech has the same cable pull ratio as the 9-speed shifters, but you may want to double check to ensure compatibility. Some recent road mechs (eg 4700) have a different pull ratio so watch out.

Now, as for capacity, you may be able to get away with it. My advice would be to make the chain long enough that cross-chaining in the big-big combination doesn't rip the rear mech off! If the chain goes slack in the opposite, small-small combination, this is less problematic IMHO. If you are confident that you wife can avoid using the small-small combo you should be able to get away with it. You might even find, depending on exact chainstay length, that it actually works fine in both extremes. (If I'm thinking straight, the mech needs extra capacity to deal with slightly longer than optimal or slightly shorter than optimal chains because chain length can only be set in 1" increments - you might get lucky and have the ideal chainstay length for your sprocket sizes)

You might be better off, however, fitting an mtb 9 speed rear mech with more capacity eg RD-M591 or 592, which both have a capacity of 45t I believe. It will be compatible. You can also go for an even lower low gear, should you wish - you can get 12-36 that would work with the M592. Don't buy an MTB 10 or 11-speed mech however, as their pull ratio is incompatible!

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DaveE128 [885 posts] 2 months ago
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Oh, and you could also mash up your own cassette, like this: http://harriscyclery.net/product/harris-custom-century-special-13-30-9-s...

Shifting might not be quite as slick, though, as the ramps may not line up as well. (not 100% sure about this).

See this page for Sheldon Brown's comments on exceeding capacity:

https://www.sheldonbrown.com/harris/derailers-rear.html#capacity

See the links in the text to understand why he says that.

 

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DaveE128 [885 posts] 2 months ago
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Oh, and if many miles have been covered, the newness of chain, cassette and mechs will probably make more difference to shifting that the bigger jumps across the cassette.

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dave atkinson [6304 posts] 2 months ago
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Because there are differences in mech position, chain line and chainstay length between bikes, manufacturers are always going to give themselves a bit of a margin. mechs that claim a 28T or 30T max sprocket can usually cope with sprockets a couple of teeth bigger, and i doubt you'll have any issues with a capacity that's one larger than what's stated.

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wycombewheeler [1100 posts] 2 months ago
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That's a very big range. I would suggest if you really need a 30 tooth large sprocket you could probably look at downsizing the 52 chairing to a 50. This would be cheaper than a longer much, but would mean moving the front mech down and so recabling and tuning.

11-28 seems fine with a 30 tooth small ring.

Is the chainset a triple? Seems like a big jump otherwise, if it is a triple the chance of ending up in small small or big big seems more remote. Agree with the statement above make sure the chain is long enough for big big (fit round the ring and cassette with no mech then add 2 links) then see what that means for small small it may or may not result in the chain passing from chainset to mech rubbing against the chain passing round the top jockey wheel.

Not desirable but not catastrophic and would only happen with using the gears on the wrong combination.

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mikepridmorewood [26 posts] 2 months ago
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I've run an 11-32 with a 52-39-30 using a RD-5701-GS (later 105 mech but remember its the shifter that does the indexing) The box states that it is up to 30 with a triple or 32 with a double but it works perfectly on mine with 32 on a triple. Did all 100 Greatest Climbs like that so should be OK  1

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mikebounds [6 posts] 2 months ago
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Thanks for all you comments - much appreciated.
If you Compare her existing 12-27 with 11-30 by offseting by 1T, then you have
12 13 14 15 17 19 21 24 27
11 12 14 16 18 20 23 26 30

So actually the difference is really you gain an extra low gear at the expense of having one wider jump at the high end (12 - 14) - other than that, you still have 3 jumps of 2T and 2 jumps of 3T, so there isn't a big change in terms of bigger steps between gears .

Having a 30T should be low enough - it is only serious hills she struggles with and she can still get up a category 3 hill - she just stops for less than a minute a few times , but doesn't walk up any of it, so she is not even sure whether she needs the 30T.

A bike shop today suggested she has an Alivio HG300 11-28 so she can keep the existing derailleur and have a very slightly bigger 28T. Never heard of Alivio before, but this seems to be for MTB, so not sure if this is ok - would be interested to know what people think and how this compares to Sora - Tiagra - 105 road range.

She does have a triple 52-42-30 and I checked 105 RD-5701 at Wiggle and this says "Compatible with 8, 9, and 10-speed drivetrains" so I assume cable pull ratio is ok.

Thanks for https://www.sheldonbrown.com/harris/derailers-rear.html#capacity link - I use this site a lot, but had only read https://www.sheldonbrown.com/derailleur.html, so this gives some reassurance that 5701 mech would be ok.
I always avoid using small-small combination anyway, but if she did go into this combo by mistake and the chain was a bit slack, what would happen, would the chain just slip a bit, or might it come off?

Thanks again for all your help.

Mike

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kevvjj [241 posts] 2 months ago
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It will work just fine. Go for it. As stated, manufacturers always err on the side of caution. I have successfully run a 30 tooth sprocket on an ancient Dura Ace derailleur which specified a max sprocket of 25 (and with a 52/39 front).

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maviczap [56 posts] 2 months ago
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What chainset are you using for this?

A 110bcd chainset can only go to 33t inner chainring.

I'm looking to have something like a 48/30 chainset, as the 30 is great for spinning up alpine climbs and 48 would be ok for the descents.

I'm not talking about old square taper ones, but newer hollowtech

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mikebounds [6 posts] 2 months ago
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Thanks again for all the replies - I did reply on Friday, but as I am a new user it didn't get checked by admins and posted until today.

In the link below (in particular posts 8 and 11):

http://forums.roadbikereview.com/components-wrenching/medium-cage-vs-sho...

it says a medium cage derailleur will shift the same as a short cage and the only possible disadvantage is the weight, but the existing RD-4400 derailleur is 280g and the RD-5701 medium cage is about 50g lighter at 232g (only 11g lighter than 5701 short cage)

So it seems to me that:

  1. The existing 9-speed Tiagra 12-27 is circa 2001 so about equiv to Sora range when it went to 9-speed and with 9-speed Sora 11-30 you effectively just have a bigger jump between 12 and 14, but you gain an extra 30T low gear (and you have an 11T which is potentially useful when in middle chain-ring).  I have tried to show comparison again below as in my last post the spaces were deleted.
    12 13 14 15 = = 17 = = 19 = = 21 =  =  = 24 =  =  = 27
    11 12  =   14 = = 16 = = 18 = = 20 =  =  = 23 =  =  = 26  =  =  =  =  30
     
  2. The 105 RD-5701 medium cage, compared to existing RD-4400 derailleur :
    - Will shift the same (or maybe better)
    - Is about 50g lighter
    - Is effectively 1-2 ranges higher as Tiagra RD-4400  is circa 2001 and 5701 is 2010+ Shimano 105 range (which is why I guess it is about 50g lighter)
    - Is 10 speed (compatible with 9 speed) so could upgrade to 10 speed shifters and cassette in the future without having to change the cage.

So the only downside is it costs £32 more to replace derailleur, but the extra 1T capacity should be fine and in the worse case you might not be able to get the small to small cog combo which you shouldn't use anyway, so my wife thinks this is worth it and so has ordered the parts today!

Mike

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maviczap [56 posts] 2 months ago
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Yes, 10 speed is compatible with 9 speed. The pull ratios changed when they went from 10 to 11 speed.

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Felltop [1 post] 2 months ago
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It'll be fine.  Exactly the setup my wife is running on her Equilibrium. 

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Simon E [3046 posts] 2 months ago
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A 3500 Sora 9 speed medium cage (GS) derailleur should be fine, they can handle up to 32t or 34t cassette used with a triple chainset. Shimano's rear derailleurs seem very similar in use, I don't think you get any better shifting with 105, it's more down to the cables and STI.

I ran 11-30 (and 12-27) with Tiagra 4500 then Sora 3500 medium cage derailleurs and a triple chainset. I didn't like the gap due to the absence of 13t on the 11-30 so fitted the 12 and 13t from a hardly used 12-27 I picked up on ebay.

Am currently using SRAM PG-950 11-28 (11,12,13,15,17,19,21,24,28) with compact chainset. You may be able to find Shimano HG61 in 11-28 (11,12,13,14,16,18,21,24,28) if you prefer that set of ratios.

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mikebounds [6 posts] 2 months ago
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 RD-5701 medium cage was fitted yesterday with 11-30 cassette and my wife is really pleased.  She can get in to all gears - the big to big rubs on the front derailleur, but this is because the chain is really diagonal in this combo, so shouldn't be used anyway and it did this with the old set-up, so my wife changes to middle ring when she is changing down and is getting near the big cog on cassette.

So now the hills are that little bit easier and she has a shiney new 105 derailleur that matches her 105 shifters.

Mike