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Nob question about chain rings 'compacts'??

Discussion in 'Bicycle Mechanics and Repairs' started by Bigtallfatbloke, 13 Jun 2008.

  1. Bigtallfatbloke

    Bigtallfatbloke New Member

    I have only ever ridden my galaxy which has a triple on it. I am about to take th eplunge into a 'proper' road bike and buy a Bianchi which only has 2 chain cogs up front..but I think one is called a 'compact' (??) Now please correct my understanding...the smaller ring here seemed to me to be a little smaller than my middle ring on th egalaxy but bigger than the third smallest ring...so am I right in thinking that the term compact has something to do with the smaller size of the second chain cog on the bIanchi?
    If I am right how does that affect the ride and in particular the transition from the bigger cog to the smaller one?

    Th eBianchi has an option to have it supplied with a triple..I dont want to make a huge mistake and order a 2 cog bike if I cant get on with the smaller 'compact' cog...erm...but I'd rather have 2 cogs than 3 to save weight and because I almost never use the third cog on my galaxy (in Essex anyway) unless it is fully loaded and I am zonked.

    Told you it was a Nob question:biggrin:
     
  2. domtyler

    domtyler Über Member

    A compact will give you just as many useable gears as a triple.
     
  3. byegad

    byegad Guru

    Location:
    NE England
    Depends on how low a gear you need for climbing. I'd need a triple for hills, you may well manage on a higher ratio than I could.
     
  4. John the Monkey

    John the Monkey Frivolous Cyclist

    Location:
    Crewe
    A "standard" road setup might be a 52T big ring with a 42T small ring. Manufacturers reckoned that this had too much top and not enough bottom, so the compact has something like 50T big and 39T small.

    The idea is that most mere mortals gain more from that because more lower gears is more useful than more big gears.

    I ride a compact triple (because that's what came on the Giant) which is 50T/39T/30T. I don't like it as much as I liked my old bike's 52T/42T, personally, but if I'm completely honest that's more because I tend to be on the big ring as soon as I've moved off, whereas on the old bike I got at least some use out of the middle ring. Also, with the 30T inner ring, and living in Cheshire, I reckon more big gears would be more useful :rolleyes:
     
  5. gbb

    gbb Legendary Member

    Location:
    Peterborough
    The transition from one chainring to the other on a compact is horrible IMO.
    You may find you need to double shift on the rear, or you end up spinning like crazy when you shift on the front.

    Its easy to fix BTFB, if you're terrain is flat(ish).
    Get a 40t (or thereabouts) and replace the 34. The transitions MUCH better.

    It's quick to do, and quick to revert back if you need, and only cost me £15.
     
  6. John the Monkey

    John the Monkey Frivolous Cyclist

    Location:
    Crewe
    This thread has some really good discussion of the benefits and otherwise (imo).
     
  7. domtyler

    domtyler Über Member

    Very true but it is easier to adapt the timing of your shifting rather than change rings imo. If you ride a compact in the same way as you ride a triple, then yes, you will get yourself into bother.
     
  8. gbb

    gbb Legendary Member

    Location:
    Peterborough
    If the chainlines the same on new Via Nirones as my 2005 model, what you will find is...
    On the 34 T(now 40 on mine), you can use it right across the cassette (9 speed), barring the smallest cog.
    On the 50 T, the chainlines poor on the 4 larger cogs on the casette.
    I find i'm on the small ring a lot.
     
  9. gbb

    gbb Legendary Member

    Location:
    Peterborough
    I spent some time looking at shifting when on different cogs on the rear...some were better, but the difference in cadence when changing on the front was still a problem.
    I see what you mean about the timing, but it means you have to lose too much cadence when going uphill before changing. A 40T ring stopped the problem in its tracks.

    Everything depends on your terrain really. There are no (or few) big hills here, so a compact was never needed anyway. Thats just what the bike came with. A normal double wasnt available.
     
  10. Joe24

    Joe24 More serious cyclist than Bonj

    Location:
    Nottingham
    Front mech has to be set up just right i find. You get so far the block, then flick the front mech lever and use the rest of the block, but the last 2 gears. Thats what i find works. When going into the larger chain ring i have to flick back through the gears(which is usually just pushing the right lever all the way) and flick the left lever so it goes into the big chain ring. So its sort of smooth going from about 19mph when in the smaller ring, to about 19.5-20mph on the larger ring.
    I dont find a problem with hills with it either. I can shoot up the hills and keep a decent cadence up.
     
  11. OP
    OP
    Bigtallfatbloke

    Bigtallfatbloke New Member

    Thanks...

    the bike I am after has shimano ultegra/105 10 speed compact (which means little to me except I am told it is all good gear).

    I cant figure out from this catalogue how many T (teeth??) the rings have though.

    I am pretty much in the hands of Bianchi and the dealer here because the bike comes as it is...BUT if any of you more experienced riders feel I could be heading for a problem with this set up please shout now & I can ask the dealer to change the cogs accordingly before I paret with my wad so to speak.

    My riding style is pretty average I would say...I plod along at about 15mph average mostly but I can and do move much quicker on occassion...like when I'm burning up a porsche at the lights or busting for a piss or something;):rolleyes:

    The arnt any hills here that demand a triple for me without panniers...so i am likely to go with just two cogs I feel, so i just want to avoid any obvious problems if I can before purchase.
     
  12. I expect that an Ultegra or 105 compact will have 50 & 34 front chainrings, that's the standard.

    You also need to know what the size of the rear cassette is - possibly 12-27 or maybe 12-25


    If you have a triple, it generally has 52/42/30 or 52/39/30 rings with perhaps a 12-25 cassette
    The highest gear you can get is the 52 vs the 12 at the back - but it's so high you'll very seldom use it except on downhills
    The lowest gear you'll get is the 30 vs the 25, which is pretty low

    On a 50/34 compact with a 12-27 cassette
    The highest is 50 vs 12, which is equivalent to 52 vs 12.5-ish on the triple and to all intents and purposes is just as high as you had with the triple
    The lowest, 34 vs 27 is equivalent to the 30 vs 25 on the triple

    So you get sort-of the same gear range on a compact as a triple

    A triple has more gears, because you've got all 30 (3 x 10) theoretically, but you can't use all of them - you can't use the smallest cogs on the cassette vs the smallest ring at the front or the largest cogs on the cassette vs the largest ring at the front, and you'll find there are duplicates - combinations of front ring vs rear cassette which are the same ratio.

    A compact saves a bit of weight, but don't get carried away it's only 100-150g
    Some think it looks a lot more swish - like a racing bike rather than a tourer with a triple.

    But there's slightly bigger gaps between the gears on a 12-27 cassette to a 12-25 and definitely a bigger gap between changing from 50-34 front rings on the compact than changing between 40-42 or 42-30 on a triple
    - you might find that if you change down 50->34 you 'go down too far' and have to change up a gear or two with the back cassette to get the gear you want : double-shifting

    I run a 50-36 compact which is better in this respect, someone further-up the thread was saying they have 50-40 : you just lose a bit of bottom-end gear.

    Well, I say I run a 50-36 : I live in Cheshire and it's fine here, but I fitted a 34 last weekend when I did White Rose Classic and it's staying on this weekend for Pain in the Pennines...

    I also run a triple on my Winter bike and practically never use the little-ring...
     
  13. ransos

    ransos Usual suspect

    No compact can match the range on my triple - 30T front and 27T rear. Nice to have with full panniers and a long hill. Plus I find a middle ring of 39T gives a much nicer range for pootling along than 34T. For the sake of 100g I'd stick with a triple.
     
  14. gbb

    gbb Legendary Member

    Location:
    Peterborough
    How's this compare BTFB..
    I'm 50, quite fit, cycled semi seriously and regularly for 5 years, terrains mostly flatish with moderately undulating hills, average 15 to 16 mph over 30 to 40 miles on a Via Nirone 9 speed compact with the 34T changed to a 40T.
    On a good flat without wind resistance, i can maintain 20 to 24 mph for some miles.
    There are no awkward changes between the 40 and 50T, i dont struggle on any of the local 'hills'.

    Changing the 34 for a 40T made the bike perfect in my case. Best thing i did...all it cost was £15.
     
  15. Nick1979

    Nick1979 New Member

    Location:
    London (SW11)
    Not on a pure road (race) bike: unless you have some serious mountains around (or tour of course), a 50/34 compact is the way to go. One guy at the LBS the other day even suggested I went for a 'standard' (for use mainly around London) but unless you need very high "racing" speeds, I'd stick with the comfort of the compact (which is found on most "entry level" road bike nowadays).

    Which Bianchi do you plan to buy BTFB? I'm spending a lot of time at the Bianchi dealer's these days as well :-)
    And isn't it a sin to put Shimano on a beautiful Italian bike BTW??