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  1. #1
    mtbr member
    Join Date
    Dec 2013

    Road FD for 50T+ gear and the largest capacity RD

    What I want is the ultimate climbing setup. This is a priority to me.
    Something like 52T(or more) and 11T

    But I also want an ultimate cruising setup. Not so much a priority.
    Cranks 30/39/50 Tiagra 4703 - 26/36/48 <-Alivio T4060-> 22/32/44

    Component Speeds do not matter so 7/8/9/10/11 speed.

    Hill climbing monster!

    There are a few steep hills I want to conquer. I measured one and it was 24% grade for a good 150m or so which had warning signs with a zigzag gate. Other hills I did not measure, no warning signs but one was a very short goat trail switch backs, maybe 15-19%.
    Another 100m
    15% Another 115m
    11% Another 200m
    Another closed road very short

    Sunrace CSM680 11-40 for $20
    - Common part cassette.

    Cruising at Speed

    I can get crank sets with 52T all day long for $5
    - Boxes full of them at community bicycle store.
    - The cruising aspect is not an issue for me, but it would be nice to have whatever is available for a decent price.

    So I am looking for the largest/biggest capacity rear derailleur possible.

    Most RD capacities seem to be around 43T and 45T.
    The 11-40 rear cassette gives it 29T capacity + whatever front I get. Time to break out the Excel Spreadsheet to maximize the cruising capabilities.

  2. #2
    mtbr member
    Join Date
    Dec 2016
    The XT M8000 RD has the biggest capacity I know of, 47T. However even that wouldn't be enough for the setup you're planning and you won't be able to make it work on an 8spd cassette because of the Dyna-Sys pull ratio. The only RD that would work for you is 7-8-9-10spd road or 7-8-9spd MTB if you are sticking to 8spd at the back. After that not just the cable pull but the pull ratios are different to SIS.

    You haven't mentioned what shifters are you using, but you have to keep in mind that if you're mixing road and MTB stuff you might run into compatibility issues both front and back.

    For riding road (or anything really) that 8spd 11-40 cassette is going to be absolutely horrible. The jumps between the gears are enormous.
    Even though you think you need 52-11, you don't. Unless you are a competitive racer on a road bike.

    A sensible setup would be a sub compact 46/30 (if you have a 68mm BB) with an 11-40 at the back, but definitely not 8spd. Or a trekking triple just not with an enormous 8spd cassette.

    Also one thing I don't understand, you say you want the ultimate climbing setup: "Something like 52T(or more) and 11T".
    What do you mean here exactly? Are you planning to climb in 52-11?

    What kind of bike is it? What kind of tyres do you have, diameter of the wheel, width of the tyre? You need to consider all of these.
    For example at the same cadence 52-11 will give you quite a different speed on 28" wheels compared to 26".
    What BB does the bike have? 68mm or 73mm? You mention both road and MTB cranksets. If the bike has a 73mm BB you won't be able to use the integrated Tiagra triple you mentioned.

  3. #3
    since 4/10/2009
    Reputation: Harold's Avatar
    Join Date
    Dec 2003
    I also have to ask for clarification on the intended setup of this bike.

    I did a similar mix of road and mtb components on my commute/gravel bike.

    My goal wasn't lowest climbing gear, though. I wanted some climbing capacity, but I wanted to be able to cruise as I was setting it up for a road century ride.

    I used a Shimano Tiagra 11spd compact double crankset (50/34) paired with a Shimano 105 5700 FD.

    2018-12-10_11-27-55 by Nate, on Flickr

    At the back end, I used a Shimano SLX 10spd M675 SGS RD and an 11-36 cassette (SRAM, I think).

    1210181100a by Nate, on Flickr

    Since it's a drop bar bike, making all this work required that I use the Gevenalle GX 10spd shifters. If I did this on a flat bar bike, then I could skip the Gevenalle and just go straight to Microshift thumbies, since that's just what the Gevenalle setup is based on (that, and Tektro drop bar brake levers).

    1210181100b by Nate, on Flickr

    I am pretty close to the posted capacities on everything. The RD has a capacity of 43t, and I'm at 41t (equation here).

    I live in a hillier place now and with TONS of gravel. I find that my compact double offers excessively tall gearing and not enough at the low end. At some point, I'll probably be dropping to a 46/30 to fit with my available riding better. If you want to mix road/mtb components like this, you need a CLEAR goal in mind so you can handle it without compatibility problems.

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