Changing Fixed/SS gearing

dhope
dhope Posts: 6,699
edited October 2010 in Workshop
Folks,

I decided to clean and regrease hub and bearings. The back wheel had a bit too much lateral play and chain a little noisy, and I wanted to learn how.
I've been thinking of increasing the gear length a bit so now seems as good a time as any.
The bike is a fixed Langster
http://www.evanscycles.com/products/spe ... e-ec001392

42 tooth chainring
Shimano 16 tooth freewheel plus a 16 tooth fixed gear cog

Is it possible to get a 13 tooth cog and leave the chainring as is. Is it just a case of finding the cog and everything else will then go back together as normal...

TIA
Rose Xeon CW Disc
CAAD12 Disc
Condor Tempo

Comments

  • andy_wrx
    andy_wrx Posts: 3,396
    Answering your question - you'll have to take a few links out to shorten the chain, but yes you should be able to take off the lockring, take off the existing cog, fit a smaller one and the lockring back again.

    But what you are proposing is a huge increase in gearing !

    42 * 16 is 70.9", 42 * 13 is 87.2"

    For street use, do you really want it that high ?

    The hire bikes at the Manchester velodrome are 84" (which would be a 14 with your 42 chainwheel), where the velodrome is designed to be ridden around flat-out, no hills, no traffic, no stopping at junctions...
  • Butterd2
    Butterd2 Posts: 937
    ^^^ Wot he said.

    Cogs are pretty cheap, try a 15 next and see how you go. I ride 48/18 which gives 72 GI's.
    Scott CR-1 (FCN 4)
    Pace RC200 FG Conversion (FCN 5)
    Giant Trance X

    My collection of Cols
  • gaspode
    gaspode Posts: 110
    also, don't forget that if you want to make use of the flip-flop rear (i.e. if you want to use it singlespeed or fixed (or want to sell it at some point)), you really want to make sure that both fixed cog and freewheel cog have the same number of teeth (otherwise you'd have to adjust your chain length each time you swap over. It would probably be more sensible to put on a bigger chainring (something like 44 or 46T) if you want to increase things more gently - check out Sheldon's calculator http://www.sheldonbrown.com/gears/ to find out the best combination....
  • Are you some sort of monster rider, or do you spin at a ridiculously low cadence?

    I ride 42 x 16 fixed on my Langster, and it's great between 18 and 23mph at that gear.
    I really wouldn't raise the gearing unless I was racing on it.
    Commute: Langster -Singlecross - Brompton S2-LX

    Road: 95 Trek 5500 -Look 695 Aerolight eTap - Boardman TTe eTap

    Offroad: Pace RC200 - Dawes Kickback 2 tandem - Tricross - Boardman CXR9.8 - Ridley x-fire
  • edhornby
    edhornby Posts: 1,780
    because you're in london you'll benefit from the flat courses you ride but 84 or 87 would be difficult to use in everyday - I ride an 80in gear and that's the absolute max I would recommend. they can be a real bvgger to get moving through sets of traffic lights, and small inclines suddenly start getting tougher when over geared.

    as andy says, increase gear size slowly
    "I get paid to make other people suffer on my wheel, how good is that"
    --Jens Voight
  • dhope
    dhope Posts: 6,699
    Are you some sort of monster rider, or do you spin at a ridiculously low cadence?

    I ride 42 x 16 fixed on my Langster, and it's great between 18 and 23mph at that gear.
    I really wouldn't raise the gearing unless I was racing on it.

    Only some light SCR, but I'd gotten used to my geared bike recently where normal would be 20mph, and needing the occasional 25, 27, 30 if passing. In London so it's flat and it was more a curiosity than anything.
    I guess I can always clean the hub now and lengthen the gear another day.
    I don't really leg brake so not too fussed about not being able to skip.

    Maybe I just need to MTFU and spin faster :D
    Rose Xeon CW Disc
    CAAD12 Disc
    Condor Tempo
  • dhope
    dhope Posts: 6,699
    edhornby wrote:
    because you're in london you'll benefit from the flat courses you ride but 84 or 87 would be difficult to use in everyday - I ride an 80in gear and that's the absolute max I would recommend. they can be a real bvgger to get moving through sets of traffic lights, and small inclines suddenly start getting tougher when over geared.

    as andy says, increase gear size slowly

    I was thinking 42/14 wouldn't be ideal given the reduced number of patches if skidding at all (hence thinking 13 as 15's very close to what I have now).
    Rose Xeon CW Disc
    CAAD12 Disc
    Condor Tempo
  • markos1963
    markos1963 Posts: 3,724
    You also have to think about chain and sprocket wear, small front and rear gears have notoriously high wear rates. Go larger on the front chainring is probably the best way to go so you get a more gradual increase in gearing. I even fitted a larger rear tyre just to get a smaller gain to match what i wanted.

    Try this calculator to help you decide which way to go, personally I think anything more than 75inches is too much but then I'm a wimp!:

    http://software.bareknucklebrigade.com/ ... pplet.html
  • Gav2000
    Gav2000 Posts: 408
    Gaspode wrote:
    also, don't forget that if you want to make use of the flip-flop rear (i.e. if you want to use it singlespeed or fixed (or want to sell it at some point)), you really want to make sure that both fixed cog and freewheel cog have the same number of teeth (otherwise you'd have to adjust your chain length each time you swap over. It would probably be more sensible to put on a bigger chainring (something like 44 or 46T) if you want to increase things more gently - check out Sheldon's calculator http://www.sheldonbrown.com/gears/ to find out the best combination....

    You can probably change a rear cog 1 tooth larger or smaller and not alter the chain length as there should be enough adjutsment in the rear drop outs. That's certainly what I used to do with my Langster when I put a 17t cog one side and a 16t on the other. Then I could quickly switch between them depending upon whether I felt energetic or wimpy.
    Gav2000

    Like a streak of lightnin' flashin' cross the sky,
    Like the swiftest arrow whizzin' from a bow,
    Like a mighty cannonball he seems to fly.
    You'll hear about him ever'where you go.
  • andy_wrx
    andy_wrx Posts: 3,396
    ^ Sheldon recommends a fixed cog one side and a freewheel 1t larger on the other side, allowing you to swap-over if tired...
    http://www.sheldonbrown.com/fixed.html
  • Never used a gear/inch calculator, but FWIW, I use 46-16 on my Langster Steel and it's fine on my local 30 miles runs, which include a few short steep hills and plenty of long inclines.
    I'm at that difficult age... somewhere between birth and death.