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Thread: Compact gears

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    Senior Member GaryPitts's Avatar
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    Compact gears

    So I went by the Harpeth River ride this weekend to check out the vendors and see Lance in person. As it turns out, he rode right by me in a pack of 8 or 10 finishing his 100 miler and I didn't even see him Crap!

    Looking at bikes in the vendor area I noticed all the fast road bikes had compact gears up front and I'm wondering now why they don't use these on all bikes instead of just the higher end road bikes? Seems that 2 gears up front would make better sense than 3, especially when I've yet to use the small front gear. I guess if I get into some serious hills I might be glad to have it, but what's the disadvantage to compact gears and why don't they use them on all bikes?

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    Some of us are poor enough on the hills that the small chain ring comes in real handy at times. I have both a compact double and a triple, and on the rides with steeper hills I will ride the triple because it is less strain to get up the hill.
    We have met the enemy and they is us.

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    Junior Member leftnose's Avatar
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    You know that "Compact Gears" doesn't refer to the fact that there are only two chainrings? It refers to the fact that the two chainrings are smaller. 50/34 is pretty typical for a compact whereas 53/39 is pretty normal for a standard double crank set.

    The *compact* double is geared lower and is a compromise between top speed and hill climbing ability while maintaining only two chain rings. Really, I think they are aimed at the amateur rider who can't push big gears from a standard up a hill.
    Last edited by leftnose; 06-14-11 at 08:01 PM. Reason: missing word

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    Senior Member Retro Grouch's Avatar
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    There are 3 factors in gearing: You'd like a gear that will allow you to pedal as fast as you're able. You need a gear that will allow you to pedal up the steepest hill you're likely to encounter. You'd also like resonable steps between your highest and lowest gears to always keep you in a comfortable RPM range.

    Standard road bike double gearing generally uses 53 and 39 tooth chainrings up front. Racers need that but, for people like me, that yields some high gears that I never use and doesn't provide low enough hill climb gears to suit my needs.

    Typical road bike triples generally provide a slightly smaller big ring and add a 30 tooth granny ring for climbing the steepest hills. They yield the widest range of gearing so, if you don't know what your needs are, a triple is the safest option.

    Compact doubles usually have a 50 tooth big ring and a 34 tooth small ring. They'll provide a high gear almost as high as the racer gearset and a hill climb gear almost as low as a triple. So what's the downside? Remember "reasonable steps to keep you in a comfortable RPM range? Compact cranksets have a bigger gap between the two chainrings. To keep the steps between gears comfortable you generally have to make 2 rear shifts every time that you change front chainrings. If the only time that you have to change front chainrings is at the top or bottom of big climbs, a compact crankset will suit you perfectly. If you find yourself having to make a lot of front shifts on a relatively flat road, you're going to hate the compact.

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    GP, Threads involving compact gearing usually draw some serious debate.

    I ride 8S road bikes and a compact crankset just doesn't allow me to fill the intermediate ratios as I like, but since the advent of wide range 10S cassettes the compact crankset has become a viable alternative, IMHO. The potential for less weight is certainly a draw for some as well for those that just don't like the look of a triple on a road bike, but still need low gearing for their most ridden terrain.

    There also maybe a marketing move towards compact cranksets as one bike wouldn't need to be built in both a double and a potentially less popular triple. The future of the triple may evolve to modified mountain bike cranksets for recreational and touring riders.

    Brad

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    Crispy Member ahsposo's Avatar
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    Quote Originally Posted by leftnose View Post
    You know that "Compact Gears" doesn't refer to the fact that there are only two chainrings? It refers to the fact that the two chainrings are smaller. 50/34 is pretty typical for a compact whereas 53/39 is pretty normal for a standard double crank set.

    The double is geared lower and is a compromise between top speed and hill climbing ability while maintaining only two chain rings. Really, I think they are aimed at the amateur rider who can't push big gears from a standard up a hill.
    Almost there.

    Compact chainrings have been around for a long time. TA marketed one in the early 1970s.

    What has changed since then is more gears and wider range in the back. Using a 11-25 with a 50/34 keeps a far amount of top end gearing and still gives a nice lower end.

    I think leftnose hit the nail on the head though Gary. You may not have been aware that there are two common sizes of double chainrings: a 53 or 52/39 (known as a standard) and the 50/34 (compact) as well as some less common variations.

    So to answer your question as I think you meant it:

    For a fit rider (not an old fat broken down roadie like myself) on a lightweight bike the standard double up front will work on just about any road you can ride on. Triples are less efficient and can be problematic as to shifting and trim. However they are priceless on loaded touring bikes or for carrying heavy riders. Often they are sold on entry level bikes because the bike frame and wheels are heavy and the assumed buyer is not necessarily very fit. Plus there is the marketing aspect (and it comes with 24 gears!).

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    Life is good RonH's Avatar
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    My Specialized (SRAM Apex) doesn't have a compact crank. Its a 52/36. Not sure what it is.
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    coprolite fietsbob's Avatar
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    3 tooth difference to 50t is not compact, 44 is.

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    Thanks for the education all. Yes, I was thinking that compact meant the 2 gears instead of the one. I'm still quite new at all this and trying to suck it all in

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    Quote Originally Posted by fietsbob View Post
    3 tooth difference to 50t is not compact, 44 is.
    44? You probably mean 46 or so and that's commonly used on cyclocross bikes.

    I wouldn't consider a 46 tooth 130mm BCD compact. Compact chainrings are typically 110mm BCD.

    From Wikipedia:

    In the context of road cycling, compact drivetrain typically refers to double cranksets with a smaller (usually 110mm) bolt circle diameter than the standard 130mm or Campagnolo's 135mm. As of 2006, all of the major component manufacturers such as Shimano and Campagnolo offer compact cranks in their midrange and high-end product lines. The compact crankset provides a compromise between the standard road double crankset (with 39/52 or 39/53 tooth chainrings) and the road triple (with 30/42/52 or 30/39/53 tooth chainrings). The compact crankset has two chainrings and typical ratios are 34/48, 34/50 and 36/50. This provides nearly the same lower gear ratios as a triple but without the need for a third chainring, a triple front derailleur and a long cage rear derailleur. Both Shimano and Campagnolo recommend and sell front derailleurs specifically designed for compact cranksets, claiming better shifting.
    Compact gearing is not necessarily lower than standard gearing if cassettes with smaller sprockets (such as 11–23) are used. A high gear of 5011 on a compact drivechain is actually slightly higher than the 5312 of a standard set.
    Compact gearing usually has a large percentage jump between the two chainrings. In balance, it may also allow small jumps in the rear by allowing a closer ratio cassette to be used, except for the 9% jump at the high end between the 11 and 12 tooth sprockets.


    And here's the link to the complete entry:http://en.wikipedia.org/wiki/Crankset#Compact_crankset

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    coprolite fietsbob's Avatar
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    Well

    they weren't called that when Maeda Sun Tour Sugino
    made the Mighty Tour 110 BCD cranks in the 80's.



    old is promoted as brand new..
    to the memory impaired, no history ..


    Wide range double , perhaps ?
    Last edited by fietsbob; 06-16-11 at 02:38 PM.

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    I was probably a relatively early adopter of a compact crank, changing about 5 years ago. I agree that 10 speed cassettes (I had 9) make them even more practical. It is rather satisfying to me to now see them spec'd. on very expensive bikes. I'm sure a big part of that is the fact that 90% or more of high end bikes will never be raced.

    FWIW - I rode this AM about 25 miles, averaging about 17.5 mph over a moderately hilly course and never got off the 34T.

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    I've been riding a 50/36 with a 9-speed 11-23 cassette for years. It's just seems too darn easy to spin out a 34t.

    Anyway, I've always maintained the principle advantage is better front shifting for spinners like myself that would otherwise be stuck with a triple. They can also be used to provide lower, near triple chainring climbing gears with better front shifting at the expense of wider gear spacing.

    If I really, really needed the lower climbing gears, I'd still go for a triple with an 12-23 cassette over a compact double with something like a 12-28. I simply find it much easier to maintain my rather high cadence while climbing with a 36t inner ring. A 39t ring either leaves me without a 14t cog in the back and a big jump between the 13t and 15t cogs or spinning out a 12t cog too easily on the steep descents that are so prevalent out here.

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    Life is good RonH's Avatar
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    From Sheldon Brown:
    Compact Crank
    A double-chainring crankset with that permits the use of smaller chainrings than will fit with the common 130 mm B.C.D. Most "compact double" cranks use the old standard 110 mm B.C.D., which permits the use of chainrings as small as 33 teeth (more commonly, 34 or 36 teeth.)

    Compact crank sets usually come with a 50 tooth chainring, and are normally used with an 11 or 12 tooth top sprocket in back.

    110 mm B.C.D. double cranks with full-sized chainrings (52-42, 52-40, etc.) were common in the late'70s and early '80s, but they had become nearly extinct for double chainrings. The rebirth of this format, with smaller rings, was pioneered by Tyler Hamilton who used one of these in the 2003 Tour de France


    http://www.sheldonbrown.com/gloss_cn...l#compactcrank
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    Quote Originally Posted by GaryPitts View Post
    So I went by the Harpeth River ride this weekend to check out the vendors and see Lance in person. As it turns out, he rode right by me in a pack of 8 or 10 finishing his 100 miler and I didn't even see him Crap!

    Looking at bikes in the vendor area I noticed all the fast road bikes had compact gears up front and I'm wondering now why they don't use these on all bikes instead of just the higher end road bikes? Seems that 2 gears up front would make better sense than 3, especially when I've yet to use the small front gear.
    You don't use the small gear because triple equipped road bikes generally leave the factory with huge cogs for tourists (who need them to get 50 pounds of luggage up hills) and out of shape people. With more reasonable cogs (I built up my first triple equipped bike with a 13-14-15-16-17-18-19-21 8 speed cassette, netting me ideal gearing for flat rides plus a low like 39x27 for mountains without needing to change wheels/cogs depending on whether the day's ride was headed west up the Rocky Mountains or east on the plains) you'd use it and may appreciate the tighter spacing.

    For the same overall range a triple provides tighter spacing between gears when
    you're not strong enough to spin a 34x26, 34x23, or 34x21 up any hill you'll encounter (with 10 cogs in back; 9 cogs reduce those to 23/21/19 and 8 cogs 21/19/18) depending on whether you prefer a 13, 12, or 11 starting cog.

    Where you are strong enough the wide crank and tight cogset combine to produce limited overlap so there's a lot more front shifting, the front shifts are more involved, you use the extreme cogs instead of ones in the middle so the bike is noisier,

    I currently use 50-34x13-14-15-16-18-18-19-21-23. Disregarding the fully cross-chained combinations the only overlapping gears are 50x21 and 34x14. With the wrong terrain, wind, fatigue, and rest-day combination situations with speed dropping to 15 MPH and exceeding 20 MPH there are a lot of front shifts.

    With the same cassette, cross-chaining avoidance, and cadence range a 40 middle ring on a triple is good for 12 - 24 MPH. While 20-24 MPH doesn't look like a lot on paper, it takes over 60% more power to get to 24 MPH. For many flat rides you can pretty much stay on the middle ring with no shifting.

    With the compact a front shift goes with five cogs in back (ex - 34x14 to 50x19 or 50x21 to 34x15) and two right shifter wiggles with Campagnolo. On the triple it'd be 3 cogs like 40x14 to 50x17 or 50x21 to 40x17.

    When cruising at a comfortable 18-19 MPH I'll ride 50x21 or 34x14 on the compact which are one cog from the end and noisy. With the triple I'd ride 40x17 (in the middle of the cassette) or 40x16 (just one off).

    I guess if I get into some serious hills I might be glad to have it, but what's the disadvantage to compact gears and why don't they use them on all bikes?
    Wider spacing between gears for the same over-all range than a triple, more double shifting, more chain noise at cruising speeds. Mountain bikers, larger riders, and people with payloads also can't get the same range out of a compact.
    Last edited by Drew Eckhardt; 06-16-11 at 04:58 PM.

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    Quote Originally Posted by cachehiker View Post
    I've been riding a 50/36 with a 9-speed 11-23 cassette for years. It's just seems too darn easy to spin out a 34t.

    Anyway, I've always maintained the principle advantage is better front shifting for spinners like myself that would otherwise be stuck with a triple.
    My 50-40-30 triple shifted better than the 50-34 compact I replaced it with after wearing out my big ring. I haven't a clue whether that's the smaller difference between rings or a difference in pins/ramps.

    Some triples can't be trimmed to be noise free, although that's a shifter problem not a triple problem (first and second generation Campagnolo ergo levers use 7 of 12 clicks for triple cranks and current production Ultrashift levers have 6)
    Last edited by Drew Eckhardt; 06-16-11 at 04:56 PM.

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    Quote Originally Posted by fietsbob View Post
    Well

    they weren't called that when Maeda Sun Tour Sugino
    made the Mighty Tour 110 BCD cranks in the 80's.
    Stronglight was making 50.4mm BCD cranks before WWII.

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