Semi compact with 11-34 cassette

Kauto5
Kauto5 Posts: 71
in Workshop
Hi all,

I'm looking at buying my friend's Giant TCR Advanced SL which he is selling. He's the same height as me so as long as the way the ISP is cut is ok, I think I'll go ahead as it's a good deal for me.

However, I'm worried about the gearing. It's a semi compact and has an 11-28 on the back which I don't think will be small enough for the riding I do (and my ability of course). I currently have a compact with a 32 on the back and use it fairly regularly on the sharp climbs I like to torture myself on in the peak district and north Yorkshire dales. It has an SS ultegra rear derailleur so I'd have to buy the GS, but I'd just like to check that buying an 11-34 cassette would be compatible with a semi compact in terms of the front mech and chainset etc? It's mechanical, not Di2.

This probably sounds like overkill but I'd rather have the added assurance of knowing I have a dinner plate on the back to save me!

Comments

  • joe_totale-2
    joe_totale-2 Posts: 1,333
    Total capacity of the GS rear derailleur is 39 teeth which is exactly the number you'd have if using a 52-36 with an 11-34 so it'll be fine:

    https://bike.shimano.com/en-EU/product/component/ultegra-r8000/RD-R8000-GS.html

    Remember to get a new chain as well.
  • bobmcstuff
    bobmcstuff Posts: 11,196
    If it's only a semi compact on there now it'll be cheaper to swap that to a compact than to buy a new derailleur. 50-34 and an 11-30 (would a 30 work on the SS?) would still be pretty low gearing.
  • Kauto5
    Kauto5 Posts: 71
    Thanks for your replies!

    Only problem with swapping to a compact chainset is that it had a Giant pro power meter, so I would ideally like to like keep that.

    I'll look a bit more into the costs and weigh it up from there.
  • super_davo
    super_davo Posts: 1,128
    You don't need to change the chainset, just the rings.
    Or if cheaper buy a new chainset and swap over. Not a hard job.
  • Kauto5
    Kauto5 Posts: 71
    Oh didn't I didn't realise you could just change the rings. That's interesting, might be my best bet actually, thanks.
  • pilot_pete
    pilot_pete Posts: 2,120
    edited July 2020
    I run Rotor chainsets on two of my bikes. One is a 52/36, the other 52/34, which I use for hillier rides. I have a short cage Dura Ace 9070 rear derailleur which handles this fine (just) and the front shifting is perfect (I run an 11-28 cassette) even though the jump between chainrings is supposedly outside of the manufacturer’s stated capacity. Maybe just try a smaller inner chainring first and see how you get on.

    PP
  • lesfirth
    lesfirth Posts: 1,382
    bobmcstuff said:

    If it's only a semi compact on there now it'll be cheaper to swap that to a compact than to buy a new derailleur. 50-34 and an 11-30 (would a 30 work on the SS?) would still be pretty low gearing.

    I will be polite and simply say that I do not agree with that.
    New rings will cost more than a R7000 gs rear derailleur. R7000 ( 105) and R8000 (ultegra) are interchangeable.
    You could buy a compact chainset off E bay and sell your semicompact there. You might even make a profit.
    However if you then find 34-30 is not low enough you will be back where you started looking for a lower gear and you have bought a new cassettte. A R7000gs will handle a cassette with upto a 36T big cog and so keeping your options to go lower open.
    Remember that it is always better to have a low gear you do not need than to need a low gear you do not have.


  • N0bodyOfTheGoat
    N0bodyOfTheGoat Posts: 5,842
    edited July 2020
    Have to say I'm loving the climbing gear options of my recently installed 11-34 cassette with 34/50 chainrings and an R7000 GS mech, for me it was so worth the swap from 11-32 cassette, the slight compromise of 2T steps when using the 50T ring when actively pedalling downhill in 15-13-11 is not an issue at all...

    Having 17-19-21-23-25-27-30-34 sprockets for climbing compared to 18-20-22-25-28-32 is wonderful!

    https://www.sheldonbrown.com/gear-calc.html is handy to see what ring/sprocket changes do.
    ================
    2020 Voodoo Marasa
    2017 Cube Attain GTC Pro Disc 2016
    2016 Voodoo Wazoo

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