How to reduce gear ratio on a triple

rkid84
rkid84 Posts: 3
edited April 2019 in Workshop
Hi everyone,

So I've got an old trek 2011 2.3 with a Shimano 105 5700 triple groupset. It has 30/39/50 and 11-28 with a medium cage rear derailleur.

My problem lies in the fact I have a sportive coming up soon which has plenty of really tough climbs and I'm not the lightest guy around.

My question can I reduce the gear ratio of the current groupset above? This isn't my usual bike and it is a one off event so I don't want to spend a lot of cash. I was wondering about a bigger cassette and a long cage derailleur?

Thanks in advance.

Comments

  • rkid84
    rkid84 Posts: 3
    Oh and I forgot to mention it is a 10 speed setup.
  • imposter2.0
    imposter2.0 Posts: 12,028
    You should be able to get a 32 or 34 cassette on the rear without too much issue..
  • Bumo_b
    Bumo_b Posts: 211
    As above, depends on the derailleur ie whether short or long cage as the back. If long cage, you can go to a 34 on the back without any trouble (slacken off the B screw). This was exactly the setup I had for L'Etape which was always going to be a huge struggle. Also, don't forget the chain length will need consideration and you might need a new longer one
  • step83
    step83 Posts: 4,170
    If its a Shimano 105 5700 medium rear it will take up to a 32T, it may need a new chain to deal with the chainring growth but a 30X32 should allow you to climb most things.
    Titanium Px Spitfire
    Easty commuter
    Tripster AT
  • mercia_man
    mercia_man Posts: 1,431
    It’s easy to get lower bottom gears on a triple like yours with a a 74 BCD little ring. Just replace your 30 tooth little chainring with something smaller. Spa Cycles, for example, will supply 74 BCD triple little rings by Stronglight and TA as small as 24 teeth to fit. I reckon you would do fine with a 28 or 26. It will only cost £17. No need to fork out for new cassette or mechs. This is what I have done to get lower gears on my Campag equipped tourer.

    https://spacycles.co.uk/m2b0s149p290/ST ... ral-24-36T
  • lesfirth
    lesfirth Posts: 1,382
    Step83 wrote:
    If its a Shimano 105 5700 medium rear it will take up to a 32T, it may need a new chain to deal with the chainring growth but a 30X32 should allow you to climb most things.

    Look at the number on your rear mech. A 5701 medium cage will go upto 32 ( I have used 34) but a 5700 will not.
  • keef66
    keef66 Posts: 13,123
    Smaller granny ring is definitely the cheapest option if the FD copes.

    I have a 5600 105 triple which is 12 years old. Well some of it is. It's so far had a new LH shifter, middle chainring, front and rear mech, and consumables like BB, cassettes and chains. Oh, and some 5800 calipers. Not quite Trigger's broom yet, but getting there.

    I'd also already gone from a 12-25 cassette to a 12-27, but the older I get the steeper the hills seem.

    Fortunately the newer rear mech is a 5701, so when I was looking for even lower gears I was able to fit an 11-32 Tiagra cassette. Just needed to add back a couple of chain links using an extra quick links and adjust the B screw a bit. Works perfectly, and if I find I'm needing a lower gear than 30/32 I think I'll start looking at e-bikes....

    Looking at the clearance twixt cassette and upper jockey wheel I guessed it would take a 34 at a push, and Les confirms as much. Might be exceeding the total capacity of the RD though, so if you size the chain to allow big-big, it'll be too long in small-small. Not that you should be selecting those extremes...

    Although having used my new lowest gear in anger for the first time on Saturday I can't imagine actually being able to use a lower one. So spinny I was in danger of falling off through lack of forward speed at times. But crucially it did get me more easily up the hill that nearly killed me a couple of weeks ago.
  • Bumo_b
    Bumo_b Posts: 211
    If you cross chain smaller to smaller, the jockey wheel does rub a little on the cassette, but I am not aware I have never been in a position that I have used this combo ( I don't think) and if I have, I have not noticed any mechanical ill effects. I have however regularly been in the large in the front and lowest in the rear before realising to drop the front.
  • keef66
    keef66 Posts: 13,123
    keef66 wrote:
    Although having used my new lowest gear in anger for the first time on Saturday I can't imagine actually being able to use a lower one. So spinny I was in danger of falling off through lack of forward speed at times. But crucially it did get me more easily up the hill that nearly killed me a couple of weeks ago.

    ETA - just checked the Garmin files for that particularly nasty little hill; max HR with the 27t cassette =167, and with the 32t = 154. It certainly felt easier!

Categories