Changing drivetrain - any help?

Specialized Needs
Specialized Needs Posts: 802
edited April 2010 in The workshop
Hi

Sorry this is a long post, but I'm thinking of getting in deeper than I ever have with fiddling with my bike. I have a 2009 Sirrus Comp, specs in the link.

So, I've trashed my drivetrain. In fact, looking at all the pointy teeth, I'm surprised it isn't doing worse than slipping when I'm out of the saddle!

The cassette and chain are straight swaps - done that before. That leaves the dérailleur jockey wheels and the frontend.

So to the questions, if anyone is able to help:

* I was thinking thesejockey wheels. Can anyone assure me that they will be OK with the tiagra long cage? And, by the way, is there a difference between the top and bottom wheels in the dérailleur? I've always wanted to know that!

* I thought of changing the whole chainset rather than just the individual rings - it works out cheaper. But I'm not sure what that is getting me into. This was the chainset I was thinking about - should it fit? Am I right to assume the crank length is measured from the centre of the bottom bracket to the centre of the pedal socket? Do I need one of these as well? Do I also need a new bottom bracket? If so, any cheap but reliable suggestions; the specs say the bottom bracket is 68x113mm?

Right - what should I look out for when doing this? What is difficult? What might go wrong? I really don't want to take the bike to pieces next weekend and not have anything to ride to work on Monday morning :?

Many thanks in advance.

Comments

  • MrChuck
    MrChuck Posts: 1,663
    I'll have a go, but don't take it as gospel!

    Those jockey wheels should fit, but if in doubt you could always just get the appropriate Shimano ones. I think on some setups there is a difference between the top and bottom ones, but if you get a pair it shouldn't really be an issue. I usually leave mine until they look like throwing stars!

    Chainset: if you got the one you've linked to, you would indeed also need the bottom bracket cups as it's a fundamentally different setup to the type you have now. If you go for that option, bottom bracket width isn't an issue as you should get spacers with the chainset to sort all that out. If you do this you don't need another bottom bracket like the one you have now: the chainset and the cups are all there is to it with Hollowtech II chainsets. Your current BB would come out and go in the spares bin.

    But if you go for this option you should really get the bottom bracket shell on the frame faced, which is a shop job and something you may or may not want to get into, maybe depending on what your local options are. You'll also need a couple of new tools: one to install the BB cups, and another to install the non-drive side crank. But it's a very easy job, there are some good videos around to help you out.

    If you don't already have it you'll also need a BB tool to get your current BB out. I'd wager that this would turn out to be the hardest part of the job- it needs a bit of grunt and it can be hard to hold the tool in place.

    HTH...
  • Specialized Needs
    Specialized Needs Posts: 802
    Thanks Mr C
    MrChuck wrote:
    I usually leave mine until they look like throwing stars!
    You've seen mine, then :wink:
    MrChuck wrote:
    But if you go for this option you should really get the bottom bracket shell on the frame faced, which is a shop job...If you don't already have it you'll also need a BB tool to get your current BB out.
    :evil: That would add to the expense. Not sure I am going to do that then - hopefully in a short while this will only be a backup bike. Well, perhaps I could still buy that chainset and swap the chainrings over. Not sure if I have a BB tool (I have a set with all sorts of weird stuff, so I might have). If I have, I may swap the BB anyhow and just keep the cranks.

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