Upgrading compact to standard chainset

designman
designman Posts: 405
edited March 2011 in Workshop
Ive got a Kinesis Racelight T2 which ive been using for my winter training which has fitted a FSA Gossamer 172.5mm 50/34 chainset...... I'm wanting to change the chainset to a standard one for the summer season, seen a Shimano 105 Octalink chainset 39/53 at a good price....
My question is - Will it fit the Kinesis Racelight T2 ok or will I need to buy a new BB?
And what is a Octalink Chainset?

Comments

  • neeb
    neeb Posts: 4,473
    Why do you want to change to a standard chainset? If you get a cassette with an 11 tooth sprocket you'll have higher gears than you need. If it's because of the big jump between the 50 and the 34 chainring you could just replace the 34T ring with a 36T.

    I might choose a standard chainset on a new bike/groupset, but I'd never bother to change a compact to a standard just because I wanted a standard. With the appropriate cassette and a 36T ring there's effectively no difference.
  • designman
    designman Posts: 405
    I can purchase the Shimano 105 Octalink chainset for £35 New.
    I guess buying cassette & chainring would cost me more...
  • John.T
    John.T Posts: 3,698
    edited March 2011
    designman wrote:
    I can purchase the Shimano 105 Octalink chainset for £35 New.
    I guess buying cassette & chainring would cost me more...
    You will need a new BB with that.
    Just fit different chainrings.
    http://www.spacycles.co.uk/products.php?plid=m2b0s149p294
    http://www.spacycles.co.uk/products.php?plid=m2b0s149p296

    This is an Octalink BB.
    http://upload.wikimedia.org/wikipedia/en/thumb/d/d8/Shimano-octalink.jpg/150px-Shimano-octalink.jpg
  • dennisn
    dennisn Posts: 10,601
    neeb wrote:
    Why do you want to change to a standard chainset? If you get a cassette with an 11 tooth sprocket you'll have higher gears than you need. If it's because of the big jump between the 50 and the 34 chainring you could just replace the 34T ring with a 36T.

    I might choose a standard chainset on a new bike/groupset, but I'd never bother to change a compact to a standard just because I wanted a standard. With the appropriate cassette and a 36T ring there's effectively no difference.

    I agree 99%. Why bother going to a "standard" crankset? Won't DO anything for you.
    Get a 36 tooth for the front if the 34 is a bit too low. As for my 1% disagree, I wouldn't bother buying an 11 tooth rear cog. You'll never use it. A 50-11 is a monster gear that
    you can't possibly push on anything except the rare downhill, and you would probably go faster just coasting.
  • designman
    designman Posts: 405
    What gear ratio would be 39 x 25 on a compact chainset?
    Is there any tables or charts which tell me the the ratios between compact & standard.
  • John.T
    John.T Posts: 3,698
    34 x 21 is just a little higher than 39 x 25. Try this table for checking gear ratios.
    http://sheldonbrown.com/gears/
  • neeb
    neeb Posts: 4,473
    Also a 36 x 23 is effectively the same as a 39 x 25
  • dennisn
    dennisn Posts: 10,601
    designman wrote:
    What gear ratio would be 39 x 25 on a compact chainset?
    Is there any tables or charts which tell me the the ratios between compact & standard.

    Don't take this wrong, but do you realize that by switching to a 53-39 from a 50-34 you won't go any faster or any easier or any longer or spin better or climb better? A crankset is not something you bolt on to a bike and are instantly transported to anything other than a new crankset on the bike. They really aren't a "upgrade" except, possibly, in the bling department.
  • rolf_f
    rolf_f Posts: 16,015
    dennisn wrote:
    You'll never use it. A 50-11 is a monster gear that
    you can't possibly push on anything except the rare downhill, and you would probably go faster just coasting.

    Rare downhill? Depends where you live. Here (West Yorkshire) the only rare gradient is no gradient!
    Faster than a tent.......
  • John.T
    John.T Posts: 3,698
    Rolf F wrote:
    dennisn wrote:
    You'll never use it. A 50-11 is a monster gear that
    you can't possibly push on anything except the rare downhill, and you would probably go faster just coasting.

    Rare downhill? Depends where you live. Here (West Yorkshire) the only rare gradient is no gradient!
    Still don't need an 11 unless you are racing. The only times I have used a 50/11 have been on gentle down hills with a big back wind during races. I regularly get over 40mph during the Circuit of the Dales TT and may even be on the 12 but I am not pedalling, this is recovery time. Never needed it any other time.