Rear Mech - what Can I Use ?

andyrr
andyrr Posts: 1,823
in Workshop
We've been given what was a nice Trek Alu-framed Madone for my daughter to use - 10 speed transmission with some 105, an Ultegra front mech etc. It unfortunately was dumped in a damp garage I think and things have seized and paint has flaked off. I managed to unseize the calipers and the gears worked ok until I found that the rear mech would not pivot cleanly. End result was a snapped rear hanger then the mech adjuster sheared off. I've a rear hanger on it's way but the rear 105 mech also has suffered damage to a cage plate so needs replaced.
I only gave the bike a quick whiz up and down the street before breaking things so I assume the mech combinations were ok but it came with the following:
11 - 32 10 speed cassette
50-32 front chainrings
Rear mech is a 5701 105 - ss/gs ? I measured the cage from centre of each jockey wheel bolt and it seems quite short at a fraction under 60mm, from reading I thought that was closer to SS spec?
I'd like to keep this range of gears, certainly on the lower ration side, just to enable my daughter to spin up the hills.

So, what can i use in place of this 5701 105 rear mech? Am I right in thinking a road 9 / 10 speed mech, other than Tiagra 4700 which has the 11 speed pull-ratio, will do, as long as it can cope with this range of gears front and back?

Comments

  • arlowood
    arlowood Posts: 2,561
    105 5701 GS rear mechs are not that easy to source but I have located one at J E James Cycles

    https://www.jejamescycles.com/product/1978/shimano-105-shimano-rd-5701-105-10-speed-rear-derailleur-gs-double-black/option/

    £55 - so not that cheap but it would be the best option to cope with the gear ratios you describe
  • andyrr
    andyrr Posts: 1,823
    Thanks - I really need to source a s/h/cheaper one to keep the overall spend down, as the bike, unless it gets a complete strip plus respray (which I don’t plan to do), ain’t worth a huge amount.
    Unfortunately being rim braked the braking tracks are pretty worn - I’ve got a couple of spare wheels fortunately - and other bits are scruffy, including spinning bolt cage rivnuts so I see it as viable only if I can reuse as much as possible and buy a few half decent bits so that it’s usable if not the prettiest.
  • Mad_Malx
    Mad_Malx Posts: 5,183
    9 speed shimano MTB RD have the same pull ratio and work fine with 10sp road shifters. But not 10sp. eg 9sp XT - this will also give the option of lower gears. Going for around £25-30 on 'bay.

  • andyrr
    andyrr Posts: 1,823
    Perfect, thanks, will have a look again : found this that confirms what you say and might help others in similar situations
    https://www.bikeradar.com/advice/buyers-guides/a-complete-guide-to-rear-derailleurs/
    .. road 10 speed (except for 4700) is compatible with MTB 9 speed. In fact it’s MUCH MORE backward compatible with other Shimano generations. For Shimano, ALL indexed 6,7,8,9 and 10 speed road derailleurs have the same cable pull ratio - the derailleur moves sideways 1.7mm for every mm of cable pull by the shifter. (with the exception, that you called out, of pre 9 speed dura ace which is on its own, and the Tiagra 4700) So for these 6-10 speed systems, its only the cable pull, determined by the shifter, that varies.
  • lesfirth
    lesfirth Posts: 1,382
    Good info above. Cheapest option will be 9sp mountain bike mech.
    A 5700 gs mech will not do.( personal experience )
  • Munsford0
    Munsford0 Posts: 680
    FWIW I have a 5701 GS rear mech working with 10 speed 105 triple 50/39/30 chainrings and 11-32 cassette. If that ever goes pop I'll be looking to replace it with a 9 speed MTB RD. Did that on the other bike so I could fit a 36t cassette...
  • andyrr
    andyrr Posts: 1,823
    lesfirth said:

    Good info above. Cheapest option will be 9sp mountain bike mech.
    A 5700 gs mech will not do.( personal experience )

    It’s a 5701 105 that came off the bike - not sure what differs between that and a 5700?
  • Munsford0
    Munsford0 Posts: 680
    edited June 2023
    Memory is hazy but a bit of googling suggests Shimano released the 5700A which increased the max sprocket to 30t. Guessing that continued into the 5701 which I can confirm handles a 32t cassette without any faffing about with the B-screw

    (My bike originally had a 5600 which only went to 28t and I ran with 25 and 27t cassettes)
  • dj58
    dj58 Posts: 2,224
    105 Series
    RD-5701-SS 30T Max Low Sprocket with Front Double
    RD-5701-GS 32T Max Low Sprocket with Front Double, 30T with Front Triple.
  • Mad_Malx
    Mad_Malx Posts: 5,183
    Never understood why Shim doesn’t use a diff number for ss gs & sgs. It’s not as if gs stands for anything obvious.
  • andyrr
    andyrr Posts: 1,823
    Mad_Malx said:

    Never understood why Shim doesn’t use a diff number for ss gs & sgs. It’s not as if gs stands for anything obvious.

    Also i don’t think the specs inc cage measurements etc, which help ID the components, are easily avail for the various flavours of rear mech, even on Shimano’s own website.
  • dj58
    dj58 Posts: 2,224
    Agree would make more sense to refer to them as Short Cage, Medium Cage and Long Cage. Alivo RD-T4000 SGS 9sp MTB gives you a 34T low sprocket.
  • secretsam
    secretsam Posts: 5,120
    You could use a Wolftooth or similar hanger extender, which would allow your rear mech to accommodate larger cassettes - they're about £20
    It's just a hill. Get over it.

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