Rear derailliur......

ted-on-tour
ted-on-tour Posts: 225
edited December 2011 in Road beginners
Just wondering the diference between long, medium, and short rear mech derailliurs?

Also any pros/cons to each...

Thanks
Pain is a momentary lapse of character.

Comments

  • nicklouse
    nicklouse Posts: 50,675
    it is to do with the range of the mech. the diference between zour big cogs and your small cogs.

    a bit of reading
    viewtopic.php?f=40043&t=12546123

    Ok it is more MTB sizes, so check yours. but the basics are the same.
    "Do not follow where the path may lead, Go instead where there is no path, and Leave a Trail."
    Parktools :?:SheldonBrown
  • ted-on-tour
    ted-on-tour Posts: 225
    Ok, makes sense.....almost.....I think.

    So if I was running 50-34 to 12-32 I would need a medium? Correct? Sorry I'm so naff at this.....I feel like i should already know!

    Anyway, next question, how does the number of teeth on a cog/sprocket affect the performance/dificulty of a riding a bike? (I'm not sure if that question even makes sense)

    Thanks.
    Pain is a momentary lapse of character.
  • keef66
    keef66 Posts: 13,123
    Ideally you want the shortest one that's compatible with your chainring / cassette combination. All to do with how much chain slack the mech can take up.

    The limitations of the mech are often described in terms of the difference between the largest and smallest chainrings, and the largest and smallest sprockets of the cassette. Added together they give the total capacity.

    eg I have a 105 triple chainset with a 30 / 39 / 50t chainrings and a 12-25 cassette. Total capacity is (50-30)+(25-12) = 33.
    This means I need the medium cage mech.
  • keef66
    keef66 Posts: 13,123
    Bike gearing is a pretty simple concept, and should allow you to keep spinning the pedals round at a comfortable speed (cadence) whatever the road is doing. Using the smaller chainring at the front is easier pedalling than using the larger one, and the reverse applies at the back where the larger sprockets are easier and the smaller ones harder.

    So when you're going up hill you tend to use the small chainring / large sprockets, and going downhill, the large chainring / small sprockets. Flat stuff, somewhere in between.
    The cassette you mentioned has a 32t largest sprocket, which is big for a road bike but would help a beginner climb hills (albeit slowly). Don't think any of the Shimano road mechs would cope with that.
    Anyway, if you are buying a complete bike, the manufacturer will have fitted an appropriate mech
  • ted-on-tour
    ted-on-tour Posts: 225
    Ok so for the most difficulty you'd have high numbers of teeth on the front and low numbers of teeth on the back, and vice-versa?

    And as for the derailliur I work it out at 36, wich is medium/large?
    Pain is a momentary lapse of character.
  • keef66
    keef66 Posts: 13,123
    ted-on-tour wrote:
    Ok so for the most difficulty you'd have high numbers of teeth on the front and low numbers of teeth on the back, and vice-versa?

    And as for the derailliur I work it out at 36, wich is medium/large?

    Most difficulty = fastest = downhill and vive versa, yes

    Which mech you need to cope with that total capacity depends on the manufacturer, the exact mech and whether it's road or mtb
  • ted-on-tour
    ted-on-tour Posts: 225
    Ok so SRAM Apex/Rival for a road bike is what I'm looking at, Could you possibly check thats correct (med/large) as I really dont want to buy one, go through all the trouble of explaning why I wanted that one to her indoors only to have the wrong one.

    I'm asking all this because I'm attempting a build soon and I've started to muddle through all the parts I'll be needing and getting together all the questions for each part (Gears and mechs and all that business confuse me).......I'm simple folk.
    Pain is a momentary lapse of character.
  • keef66
    keef66 Posts: 13,123
    So are you buying the complete groupset? That makes things easier.
  • keef66
    keef66 Posts: 13,123
    eg Merlin have the Apex groupset for £400

    http://www.merlincycles.co.uk/Bike+Shop ... -OFFER.htm
  • keef66
    keef66 Posts: 13,123
    Apex has the 11-32 cassette and comes with the medium cage rear mech

    The Rival groupset is quite a bit dearer but has more conventional road cassette options
  • ted-on-tour
    ted-on-tour Posts: 225
    No I'll be buying it one piece at a time ( limited funds)

    So I think I'll be taking your advice Keef, thanks for your help.

    Dan
    Pain is a momentary lapse of character.
  • John.T
    John.T Posts: 3,698
    ted-on-tour wrote:
    No I'll be buying it one piece at a time ( limited funds)
    Cheaper to get a groupset if you need all of it. Just save up and then take the plunge.
    I would also suggest you use the time to find out what you actually need for the type of riding you intend doing. Find a 'proper' bike shop run and staffed by cyclists and talk to them. They can show you things better than asking on here.
    My Fleet.

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