Converting from 53/39 50/34 cheaply

louman999
louman999 Posts: 90
edited May 2016 in Road general
I currently have a 105 53/39 crankset. I have quickly realised I need a 50/34. Originally I was going to buy new chainrings but I can't find both chainrings sold together. Individually they are a ripoff for a piece of metal. I've seen some cheap FSA cranks but they are for BB30 and I have hollowtech II. Any suggestions on what to do ???

Comments

  • Sleeper Service
    Sleeper Service Posts: 126
    Buy a 105 compact crankset? Currently £73 from Wiggle.
    Carrera Subway 2015
    Boardman Hybrid Team 2014
  • simon_masterson
    simon_masterson Posts: 2,740
    If you could do it by changing chainrings, the compact chainset wouldn't exist. Go on eBay or forum classifieds.
    Retro(ish) TT 2017-
    Fixed TT 2015-2016
  • sungod
    sungod Posts: 17,379
    Louman999 wrote:
    I currently have a 105 53/39 crankset. I have quickly realised I need a 50/34. Originally I was going to buy new chainrings but I can't find both chainrings sold together. Individually they are a ripoff for a piece of metal. I've seen some cheap FSA cranks but they are for BB30 and I have hollowtech II. Any suggestions on what to do ???

    your cranks are likely to be 130bcd, you cannot physically fit compact rings to 130bcd cranks, you need 110 bcd, so you'd need to buy a complete crankset

    what cassette do you have? if it's an xx-25 then fitting one with a 28 would give you a gear almost as low as switching to a compact
    my bike - faster than god's and twice as shiny
  • louman999
    louman999 Posts: 90
    I'm just about to replace my cassette from an 12-25 to 12-30. However I still find the 53 to big and so I think I will be better with a 50. Looks like I will have to replace the whole crank that will be cheap.
  • louman999
    louman999 Posts: 90
    Just another question can I fit cranks that are designed for bb30 in hollowtech II ???
  • nochekmate
    nochekmate Posts: 3,460
    Louman999 wrote:
    Just another question can I fit cranks that are designed for bb30 in hollowtech II ???

    Nope - spindle is different diameter. You can do it the other way round though with various adapted BB designs.
  • paul2718
    paul2718 Posts: 471
    If this is 105 5700 then you will need a new crank, if 5800 then you can swap the rings because all the cranks are the same BCD. But a pair of rings costs almost the same as a crank. About £70 regardless.

    You can get adaptors to fit 24mm Hollowtech II (BB86 or BB90?) to a BB30 frame, but vice versa would seem less obvious, I can't find one at a glance but I'm not an expert, and whichever you are adding expense and complication.

    Paul
  • sungod
    sungod Posts: 17,379
    Louman999 wrote:
    I'm just about to replace my cassette from an 12-25 to 12-30. However I still find the 53 to big and so I think I will be better with a 50. Looks like I will have to replace the whole crank that will be cheap.

    going from 53 to 50 makes less difference than one cog on the cassette, not much return for such an investment

    as you're putting a 12-30 cassette on, it's really only worth changing the crankset if need 34-30 instead of 39-30, i'd really wait and see how you find it before changing crankset

    btw is your rear mech ok with a 30t maximum on the cassette? not all are rated for that
    my bike - faster than god's and twice as shiny
  • MikeBrew
    MikeBrew Posts: 814
    sungod wrote:
    going from 53 to 50 makes less difference than one cog on the cassette, not much return for such an investment

    To me, going from standard to compact is really more about the spread of lower gears that the 34 (or 36) inner ring gives. I quite like a 53 ring but the 39 inner (38 minimum) that 130 BCD caters for just doesn't give a nice RANGE of lower gears for the steeper stuff.
    I know that you can stick a longer cage rear mech and a 32 sprocket on a bike with standard gearing and get a lowest gear equal to some compacts, but you get larger gaps between the ratios. Also it's often just as much hassle and expense as buying a compact crank-set.
    And 39 32 will always being a higher gear than 34 32. One of the daft things about cycle spares prices is that it's often as cheap (or cheaper) to buy a cheap crank-set as two brand new rings...
  • whoof
    whoof Posts: 756
    Louman999 wrote:
    I'm just about to replace my cassette from an 12-25 to 12-30. However I still find the 53 to big and so I think I will be better with a 50. Looks like I will have to replace the whole crank that will be cheap.

    When you say the 53 is too big when are you using it?

    If it's just the top end 53/12 or 50/12 there's not much in it. If you pedal at 100 rpm then in 53/12 you go 34.6 mph and in 50/12 you go 32.6 mph.

    If it's because you're riding in the 53 on the flat at 'middling' speed and it's too hard then use the 39 ring. A lot of people use the 50 on a compact for most riding other than going up hill. Turning your legs at 90 rpm in 50/21 you will go about 16 mph. With a standard road you can use the 39 for these middling speeds. If you have 53/39 then use 39/17 and you will also go about 16 mph.

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