Changing from a Compact to Double chainset - what impact?

Weeman1973
Weeman1973 Posts: 471
edited February 2013 in Road buying advice
I had a Retul fitting at the weekend and found out that my perfect crank length is 167.5mm as opposed to the 170 I currently ride. Whilst not making a huge difference, I would like to try this combo but have found it's only really Dura Ace that make this length which equals pricey.

I have found a Double Dura Ace Chainset that isn't too expensive so may give it a go but it's a regular Double 53/39 as opposed to my current Compact set up of 50/34. Am I going to notice a significant difference?

I am not into Stelvio style climbing (living in Cambridgeshire!) so very rarely use my largest cog on my rear cassette (12/25) so doubt it would be an issue. To counteract the higher gearing at the front, could I put an 27 cog on the rear?

Will I have to amend my current chain length to accommodate the larger chainset / cassette?

Comments

  • awsm
    awsm Posts: 210
    If you're not riding up hills all the time you should be fine, the main differences are at the opposite ends, comparison of the change here:

    http://www.gear-calculator.com/#KB=34,5 ... =2099&SL=2
  • rolf_f
    rolf_f Posts: 16,015
    You'll be doing well if you can find anyone on here who can convincingly claim to have noticed a 2.5 mm crank length difference. Not so much 'not a huge difference' as an almost infinitesimally small difference!

    If someone showed me that my crank lengths were wrong I would consider changing next time I needed a crankset but I doubt I'd change until then.

    That said, if you can't manage with a 53/39 in Cambs, where could you manage with one! A bigger cassette will restore your range if you need it to.
    Faster than a tent.......
  • Rolf F wrote:
    You'll be doing well if you can find anyone on here who can convincingly claim to have noticed a 2.5 mm crank length difference. Not so much 'not a huge difference' as an almost infinitesimally small difference!

    If someone showed me that my crank lengths were wrong I would consider changing next time I needed a crankset but I doubt I'd change until then.

    That said, if you can't manage with a 53/39 in Cambs, where could you manage with one! A bigger cassette will restore your range if you need it to.
    Totally agree and am only thinking of changing chainset to have a regular 53/39 double as opposed to the the compact 50/34 - whilst I am at it, might as well see if I can try the smaller cranks at the same time.

    If I were to change to 53/39 and 12/28 cassette, would I need to add links to the chain as my current chain is set up for 50/34 and 12/25 cassette (through a Force rear mech)?
  • Yes you would need a longer chain, as you have a bigger 53 chainring and you may well go to a bigger 28 rear cassette.

    Personally, I would advise against this move unless you're a very strong rider and can happily turn a 53/14/13/12 on the flat.

    Because although you're not troubled by big hills, if you do change cassette you will have a bit more of a gap between gears. The chainset, chain and cassette will all be slightly heavier, if you're into the whole weight thing....!

    And one day - you may hit some hills - sportive, trip to the Alps, etc.

    167.5 is a size you don't see very often, so resale may be tricky. 170 is already what most riders generally feel is the normal minimum.

    Personally, I wouldn't bother.
  • Yes you would need a longer chain, as you have a bigger 53 chainring and you may well go to a bigger 28 rear cassette.

    Personally, I would advise against this move unless you're a very strong rider and can happily turn a 53/14/13/12 on the flat.

    Because although you're not troubled by big hills, if you do change cassette you will have a bit more of a gap between gears. The chainset, chain and cassette will all be slightly heavier, if you're into the whole weight thing....!

    And one day - you may hit some hills - sportive, trip to the Alps, etc.

    167.5 is a size you don't see very often, so resale may be tricky. 170 is already what most riders generally feel is the normal minimum.

    Personally, I wouldn't bother.

    To be fair I don't need a new chainset as my 105 is 50/34 and 170mm and relatively new - was just looking for next time but as you say probably not worth the hassle.

    I need a new cassette anyway as have bought some new wheels and can't be doing with changing cassette ever time I change the wheels over so was thinking of changing the gearing there instead as an option. If I went with say 11/27 or 12/28, would I need a longer chain then do you think - if so, really not worth it I guess.
  • If you stay with the compact and move from a 25 to 27 cassette you might get away with it depending on who built your bike and how long your chain is - it may have enough slack - put it into 50-25 and see how stretched the derailleur is - that will give you some idea.
  • rolf_f
    rolf_f Posts: 16,015
    Needing a longer chain isn't a reason to make the decision one way or another. Chains wear out by mileage so having a second chain for a second cassette doesn't cost anymore in the long run. Swapping the chain off the bike is no bother if you use quick links and if you are going to the trouble of swapping cassettes, presumably you'd take that opportunity to clean the chain properly (ie off the bike) anyway.

    I take the cassettes off regularly as well anyway - just to keep them clean.
    Faster than a tent.......