Needing lower gears

fredmac
fredmac Posts: 83
edited November 2010 in Workshop
For a few years now I have been running a campag compact chain set, 10 speed veloce with 25 teeth on the lowest gear. This has served me fairly well as there are quite a few steepish hills where I live (Galloway, Scotland) and I also usually do some cycling in the Highlands as well.
However I recently bought another bike, which was second hand so I didn't have any choice on the gears. This bike has an Ultegra group set with a standard chain set and the cassette is 11-21. So as you can see I have lost quite a bit of gearing at the bottom end, where i need it!
Looking around it seems the lowest gearing I can get is 12-27 which wuold be a help.If I put one of these on are there other issues like chain length that I would need to consider?
Or are there other ways to get more teeth on the big cog? A cassette of 13-29 or 14-30 would suit me fine, is there any way of getting this?
Hopefuly some of you guys will have some anwers for me.

Comments

  • sungod
    sungod Posts: 16,432
    how far you can go depends on the rear mech

    it has two specifications that matter

    i) largest cog allowed on cassette

    ii) maximum capacity - capacity is the sum of the differences between big/small chainring and smallest/largest cogs, so 53/39 is 14, 11-21 is 10, sum of 14+10 is capacity of 24

    check which rear mech you've got, look up the spec, shimano is all here...

    http://techdocs.shimano.com

    ...and you can see what options are open to you, to fit a really big cassette you'd probably have to change the rear mech

    if you can't get the cassette size you want from shimano try sram, they're compatible
    my bike - faster than god's and twice as shiny
  • rhnb
    rhnb Posts: 324
    These lot will sort you out...

    http://www.highpath.net/

    Click the Marchisio link on the left.

    Can thoroughly recommend them.

    Cheeers... Allan.
    ~~~
    http://www.bikeit.eclipse.co.uk
    Cycle tour reports and the home of \'Cycling Before Lycra\'
  • ChrisSA
    ChrisSA Posts: 455
    Plus you can run a few more teeth than Shimano spec. I was running an 11-28 with a 50/34 - which was 33T all in.

    Just don't cross chain!
  • andrew_s
    andrew_s Posts: 2,511
    Shimano road mechs officially stop at 27T, but can usually be persuaded as far as 30T by fiddling with the chain length and B screw. The problem isn't cage length but the top jockey wheel hitting the big sprocket. Beyond 30T you will need an MTB rear mech.

    I assume that the Ultegra is 10 speed. Shimano road cassettes stop at 27T, and MTB 10 speed has only just been introduced so there isn't much choice at the cheaper end yet.
    There's SLX 11-34 (£40), XT 11-34 (£48), SRAM PG1050 11-32 (£50) at Chainreaction,
    or see St John St for other options.

    Chain should be long enough to be able to change on to big/big. If it isn't and you inadvertently select that gear, you could well break something. Picking the wrong gear is easily done if you ever ride in the dark. It might mean you get slack chain in small/small, but you shouldn't use those gears anyway,and nothing drastic will happen if you do select it.
  • ChrisSA
    ChrisSA Posts: 455
    andrew_s wrote:
    Shimano road mechs officially stop at 27T, but can usually be persuaded as far as 30T by fiddling with the chain length and B screw. The problem isn't cage length but the top jockey wheel hitting the big sprocket. Beyond 30T you will need an MTB rear mech.

    The new 105 and Ultegra short cage do 33T. As above, I got 33T on my Tiagra 4400 short cage.
  • Thanks for the help so far guys.
    andrew_s --it's a nine speed cassette, will that make much of a difference?
    I've had a look at the rear mech and I think it is the short cage version, going by the diagram on the shimano web site. Also when the gears are in large- large the jockey wheel is fairly close to the cassette, does this mean I will need a longer chain and if so how do you work out how much longer you need?--all very confusing.
    rhnb-- had a look at highpath engineering and that looks quite promising as they do a 14- 28 tooth cassette for shimano 9 speed .
    This would give a capacity of 28, would this work or not?

    Thanks again
  • ChrisSA
    ChrisSA Posts: 455
    28T works well, but those cassettes are expensive!

    The way most people size a chain is putting it over large-large, but not through the rear mech.

    However large-large and small-small should be avoided when actually riding the bike. It's bad to cross chain (also small-small). 52x28 is the same as 39x21, so the same ratio is achievable in the smaller chainring.

    SRAM do a 9 speed 11-32 . With a 52/39 chainset this could be do-able with care on a short cage. They also do a 11-34 but that would need a long cage mech.
  • k2rider
    k2rider Posts: 575
    put a mtb rear mech and cassette on it.
    who cares?
  • To get 28 teeth from these cassettes from highpath would cost another 20 quid, would it make all that much difference? Probably would be quite glad of it when struggling up some mountain in the highlands.
  • John.T
    John.T Posts: 3,698
    Just fitting a 12/27 cassette will lower your bottom gear by 20% which is a very good start. You should fit a new chain with a new cassette anyway so just set the length then.
    If you need lower still then your options are a compact chainset or MTB cassette and rear mech (9sp one as the 10sp use a different cable pull). You could push the big sprocket as far as 30 with care but you are pushing the mech limits and the cassette options are not cheap. Better and safer to stay with standard stuff.