Bigger road cassette range - Shimano 9/10 speed compatibility question

jas0_0
jas0_0 Posts: 4
in Road buying advice
Hi all,

I wonder if you could help. My Dad has an early 2000s Peugeot road bike with a (mainly) Tiagra 9 speed groupset and we want to replace the cassette to help him on the Somerset hills - the largest sprocket is currently just 23T.

He isn't bothered about having more gears and I see that Shimano makes a 9 speed HG400 11-34T cassette, and compatible chain, which seem ideal. To fit these we will also need to replace the Tiagra rear derailleur as his is short cage and maxes out at 27T. I realise we could just get the current Sora 9 speed GS derailleur and have done with it, but dropping the rear mech from Tiagra to Sora bothers me!

Could we use a current 10 speed Tiagra GS derailleur with a 9 speed Sora cassette/chain, or will we get into chain clearance issues on the cage and jockey wheels?

Many thanks in advance.

James

Comments

  • helterskelter
    helterskelter Posts: 66
    It should run with the shifters as they are what dictate cable pull and amount of shifts. 9/10 speed seems to be a common standard for jockey wheels so shouldn’t be an issue.
  • whyamihere
    whyamihere Posts: 7,700
    helterskelter said:

    It should run with the shifters as they are what dictate cable pull and amount of shifts. 9/10 speed seems to be a common standard for jockey wheels so shouldn’t be an issue.

    That's incorrect. The pull ratio of the shifter needs to match the pull ratio of the mech, and Tiagra 10 speed doesn't match Shimano 9 speed.

    The 9 speed Sora should work, and it's not really a downgrade because of the way Shimano trickle down features. The other option is a 9 speed MTB mech if you can find one - The Shimano 9 speed road and MTB systems used the same pull ratio.
  • masjer
    masjer Posts: 2,555
    As above, the MTB 9 speed derailleur is a good option. You can use the more modern type (shadow). I use a Shimano RD-M3000 on my winter bike
    , it works well and can be found cheaply.

    https://bike.shimano.com/en-EU/product/component/acera-m3000/RD-M3000.html
  • lesfirth
    lesfirth Posts: 1,382
    helterskelter said:

    It should run with the shifters as they are what dictate cable pull and amount of shifts. 9/10 speed seems to be a common standard for jockey wheels so shouldn’t be an issue.

    To say that is" incorrect " is being very polite. In fact it is total efin b0llocks. The OP wants to know what WILL work. Telling the OP what " should or seem to" work is no use. When you obviously have no idea you are better keeping your fingers off the keyboard.
    I have not looked in the mirror but I must have my grumpy old mans hat on this morning.
  • PMark
    PMark Posts: 159
    The Sora one will probably be a bit lighter, but the advantage of a MTB one is you could go to a 11-36 rear cassette if you desired.
  • helterskelter
    helterskelter Posts: 66
    lesfirth said:

    helterskelter said:

    It should run with the shifters as they are what dictate cable pull and amount of shifts. 9/10 speed seems to be a common standard for jockey wheels so shouldn’t be an issue.

    To say that is" incorrect " is being very polite. In fact it is total efin b0llocks. The OP wants to know what WILL work. Telling the OP what " should or seem to" work is no use. When you obviously have no idea you are better keeping your fingers off the keyboard.
    I have not looked in the mirror but I must have my grumpy old mans hat on this morning.
    He already knew what would work, the sora one.... Whilst not an out the box solution the 10 speed is probably a workable solution if you disregard what the Shimano rules tell you. Depends how adventurous you are. Get a coffee in you and cheer up.
  • whyamihere
    whyamihere Posts: 7,700
    helterskelter said:

    lesfirth said:

    helterskelter said:

    It should run with the shifters as they are what dictate cable pull and amount of shifts. 9/10 speed seems to be a common standard for jockey wheels so shouldn’t be an issue.

    To say that is" incorrect " is being very polite. In fact it is total efin b0llocks. The OP wants to know what WILL work. Telling the OP what " should or seem to" work is no use. When you obviously have no idea you are better keeping your fingers off the keyboard.
    I have not looked in the mirror but I must have my grumpy old mans hat on this morning.
    He already knew what would work, the sora one.... Whilst not an out the box solution the 10 speed is probably a workable solution if you disregard what the Shimano rules tell you. Depends how adventurous you are. Get a coffee in you and cheer up.
    No, it's not a workable solution.

    9 speed Shimano had a pull ratio of 1.7. That means that for each 1mm the cable is pulled, the derailleur moves 1.7mm. Current gen Tiagra 4700, which is the one which adds support for 34t cassettes in the GS model, uses a pull ratio of 1.4. This is marked in compatibility charts as only working with Tiagra 4700 shifters, but is actually the same pull ratio as 11 speed, not that that's relevant.

    The problem here is that the Tiagra mech won't move far enough for the shifting to work properly. You may get it to shift across one or two gears, but not across the range. Tiagra 4600 used the Shimano 10 speed pull ratio which was the same as the 9 speed at 1.7, but didn't support a 34t cassette officially. That *might* work, but it's dependent on a lot of variables.
  • rik.j.rayner
    rik.j.rayner Posts: 12
    I found this online resource which may help the OP - https://bike.bikegremlin.com/1278/bicycle-rear-derailleur-compatibility/

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