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Compact to Triple - 10spd

Mike HowarthMike Howarth Posts: 75
edited November 2009 in Workshop
I'm planning on taking my Kaffenback touring in New Zealand in December.

At the moment I'm sporting a compact chainset and whilst its been plenty low enough geared for all my usual riding I just can't see how I'm going to get by on a fully laden bike riding a compact.

I built the Kaff up with the guys at Planet X and think it should be relatively straightforward.

Heres my thoughts wouldn't mind someone just validating what I'm thinking and whether I've missed anything.

As I see it the main components are:

Shifters - 105 - understand these are interchangable and and can run double/triple
Front Derailleur - Ultegra - will need swapping for a triple
Rear Derailleur - Ultegra short cage - will swap this out for an old XT long cage rear mech
Cranks - Ultegra compact will need swapping for a triple
Bottom Bracket - 105 - think this is a universal b/b for both double and triple?
Casette - bit stumped on what to do with this. Have looked at some of the IRD casettes to get some low gearing but they're not cheap
Chain - will need to add some more links

Posts

  • sheffsimonsheffsimon Posts: 1,282
    Not sure why you need a longer chain and long cage rear mech??

    Are you fitting a with much bigger sprokets? Even if so, you arent going to be using the largest tooth sprocket on the the big chainwheel, so no need for more chain for that reason, and presumably your largest chainwheel on the triple wont be bigger than 50-ish?
  • Sorry I was probably a little quick to hit the submit button.

    Basically I'm thinking of also dropping the rear casette down from a standard 27t rear block to something more suitable to touring. Maybe 11-25 or lower.
  • Mister WMister W Posts: 791
    You may need a longer cage rear mech even if you don't change the cassette because the short cage mech may not take up enough chain slack when you're on the small ring. Check the Shimano website to see how much each mech will cope with. It will be shown as a maximum front difference (i.e. the difference in the number of teeth between the smallest and largest chainrings) and the total capacity (the difference between the the largest number of teeth the chain is going round and the smallest number of teeth). So, if you have a 52 45 30 chainset with a 12-25 cassette you'll need a rear mech with a total capacity of (52+25) - (30+12) = 35.

    In reality you probably won't use the extreme combinations (big chainring with big cog or small chainring with small cog) but it's nice to know that if your mech will cope if you do select them by accident.
  • Thought as much on the mech front. I think I'll be able to pick up a cheap XT rear mech on e-bay or similar.

    What are peoples thoughts on 10spd rear casettes. From what I've seen I haven't seen any Shimano casettes go lower than 12-27T.

    Are the IRD casettes the only way to go, and does anyone know of UK stockists as IRD don't do international shipping apparently.
  • John.TJohn.T Posts: 3,698
    If you use the XT mech you mentioned you can run any size rear cassette up to about 34 teeth. You would need to get a custom one for anything larger than a 28 (SRAM)as there are no larger 10sp ones. (except SRAM X10 which cost a fortune). 28 teeth is the largest you can run on a 'road' mech but the MTB ones go larger.
    You should fit a new chain of the correct length. Adding links to an old one is not such a good idea.
    If you swap the cassette from a 27 to a 25 and go to a triple with a 30 inner ring from a 34 you will have almost the same bottom gear so is it worth doing at all.
  • John - you get a bonus prize for spotting the obvious mistake.when I was quoting 11-25 I was going the wrong way.

    What I actually mean't to say was 11-32 or even 11-34. I reckon that would give me a fairly nice granny gear to spin up some of the mountain passes in NZ.
  • John.TJohn.T Posts: 3,698
    With 10 sp your only real option is a custom cassette. You can go up to 30 with a Marchisio or 34 with IRD.
    http://www.parker-international.co.uk/3981/Marchisio-Aviotek-Shimano-10-speed-Cassette.html
    http://store.interlocracing.com/10elcas.html
  • ProssPross Posts: 31,576
    Don't you start to effectively lose the benefit of having a smaller chainring the larger you go with a sprocket? For example a 34 - 23 gear is roughly 4.6" longer than a 30 - 23 but it would be down to 3.6" by time you get to a 29 tooth sprocket. Not saying it isn't worth getting a triple as you'll obviously have a better overall range just a case of diminishing returns on the lowest gear as the sprocket gets larger.

    BTW According to Sheldon Brown Shimano do a 13 - 29 10 speed cassette.
  • John.TJohn.T Posts: 3,698
    Pross wrote:
    Don't you start to effectively lose the benefit of having a smaller chainring the larger you go with a sprocket? For example a 34 - 23 gear is roughly 4.6" longer than a 30 - 23 but it would be down to 3.6" by time you get to a 29 tooth sprocket. Not saying it isn't worth getting a triple as you'll obviously have a better overall range just a case of diminishing returns on the lowest gear as the sprocket gets larger.
    BTW According to Sheldon Brown Shimano do a 13 - 29 10 speed cassette.
    Yes to some extent this is true, which is why I always recomend a 12/27 over a 12/25, but if you want lower gears there are only 2 ways to go. Bigger sprockets or smaller chainrings. Road chainsets only go down to 30 teeth and touring / MTB ones bring in problems with front mechs. A road one does not work well because the cage is profiled for a 53 ring and an MTB one is designed for a slacker seat tube angle. It also has a different cable pull (this is not insumountable).
    I can not find a Shimano 10sp 13/29 cassette on SB. And definately not on the Shimano site.
  • Thanks for all the comments on this. Just bringing this one back from the dead before I go out and do some spending.

    Had a bit of a change in thinking. At the moment I'm thinking that I'm probably going to give the IRD casette a miss and probably look at using a 9 speed mtb rear block (11-34) use the alternate cable position to mix and match the 10sp shifters and the 9sp block.

    Obviously whilst switching the block I'll put an XT rear mech on and put a new 9sp chain and power link on.

    Up front I'm a bit unsure what do. Looking at things I'm thinking about putting an LX hollowtech crank on which would mean I'd need to look at putting an MTB front derailleur.

    I'm wondering whether road shifters and mtb front mechs are actually compatiable though. Any ideas?

    Anyone see anything glaringly wrong with my thinking?

    I'm sort of thinking I'll use this kit to tour on and may just swap back once to the existing kit once I'm back but who knows.
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