Compact v not compact

by mancsi   December 21, 2011  

Can somebody please tell me the difference between the above?

Ta

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Typically 3 teeth on large chainring, 5 on small.

arrieredupeleton

posted by arrieredupeleton [563 posts]
21st December 2011 - 13:38

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its to do with the chainset, more specifically the front rings.

If you imagine you have a bike with triple chainrings at the front, you'd reasonably expect that it could cover a wider range of gear ratios than a bike with just double chainrings. And historically this would have been true.

However, where the compact chainset comes in is that you just have the two rings, but the number of teeth they have gives you broadly the same range of ratios as if you had a triple. So they've "compacted" from 3 rings to 2.

Pete

PeteH's picture

posted by PeteH [159 posts]
21st December 2011 - 13:40

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Nice one for that Pete

2 wheels please!

posted by mancsi [119 posts]
21st December 2011 - 13:42

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Pete, I think he means the difference from a 'standard' chainset of 53/39 compared to a compact of 50/34.

A compact is unlikely to give the range of a triple unless you increase the sprockets. The Sram Apex grupo is the exception as it was designed as a 'compact' with the range of a triple and hence a long cage rear mech with a 11-32 block on the back.

If you need to compare different size chainsets and sprockets, look at Sheldon Brown's website:

http://www.sheldonbrown.com/gears/

arrieredupeleton

posted by arrieredupeleton [563 posts]
21st December 2011 - 13:44

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I think a compact makes sense for many riders, in place of a standard racing double chainset. It gives you a reasonably low bottom gear for winching up hills. But there is a big jump between gears on a 50/34, so when changing the front you'll often need to change the rear as well. I think that a "cyclo-cross" 46/36 compact is nice for non-racing leisure riders - you can ride most of the time in a sensible gear in the big ring, less of a gap to the small ring, and still have a reasonably low bottom gear.

two wheels good; four wheels bad

posted by cat1commuter [1360 posts]
21st December 2011 - 15:30

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and just to be confusing 'compact' can also refer to frames - those with very sloping (front to back) top tubes are called compact as they're smaller than traditional horizontal top tubed frames.

TheHatter's picture

posted by TheHatter [811 posts]
21st December 2011 - 17:16

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Where will you ride? Hills or flat areas?

I love the 53/39 in Cambrideshire and in Somerset I needed a 12-27 cassette or a compact in the hills.

Some riders look down on a triple. But if you are injured, heavy or have health issues, then why not use a triple.

I only found I took ages with a front mech/triple setting it up.

Sram's Apex range of gears is a good option too.

I like my bike but it needs a hidden 25cc motor Smile

Fish_n_Chips's picture

posted by Fish_n_Chips [325 posts]
21st December 2011 - 17:29

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Add in 11 speed too...

when I specced my new bike last year I was going to get standard 39-53 front rings. But in that case I would have gone for 12-25 at the back.

With a compact 34-50 and 11-23 I have a wider range, including a higher 'top' gear and a lower bottom gear, and closer to a straight block.

The other answer to your question is that a Compact front often attracts scorn from people who don't regard it as 'serious' for racing and fast riding. Possibly true in the days of 9 and 10 speed but less so now.

abudhabiChris's picture

posted by abudhabiChris [543 posts]
21st December 2011 - 17:40

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Fish_n_Chips wrote:
Some riders look down on a triple. But if you are injured, heavy or have health issues, then why not use a triple.

Those riders are poorly educated or plain ignorant.

I am 64kg, healthy and ride a triple. I like the fact that the 39T middle ring covers a decent range of gradients and I'm in the middle of the cassette's range a lot of the time, whereas with a 50/34 compact I'd often be riding on big-big or small-small. The additional 250g over a compact does not keep me awake at night.

Returning to the OP, the 50-tooth outer ring of a compact (50 and 34 teeth) is only slightly lower gearing than the 52 teeth of a standard double (52 and 39) so there's no real difference on the flat or downhill.

However, the 34-tooth inner gives noticeably lower gears for us mortals to keep pedalling up steep or long hills without needing a big MTB cassette on the back, which would otherwise require a MTB-specific rear derailleur. David Millar did the latter for some stages of this year's Giro d'Italia.

The compact's range is close to that of a 50/39/30 triple, though there is a big jump in ratios when you switch chainrings.

Graph of compact ratios compared to my old 52/42/30 triple:

http://www.flickr.com/photos/ruralwales/2570786321/

Hope that helps.

Simon E's picture

posted by Simon E [2008 posts]
22nd December 2011 - 13:52

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Simon E wrote:
Fish_n_Chips wrote:
Some riders look down on a triple. But if you are injured, heavy or have health issues, then why not use a triple.

Those riders are poorly educated or plain ignorant.

Totally agree, I used a triple and stormed up hills that my friends struggled up.

I use a double now as I can.

I will be buying my old man a triple or maybe Apex as he is quite old and not very fit but he loves cycling.

I like my bike but it needs a hidden 25cc motor Smile

Fish_n_Chips's picture

posted by Fish_n_Chips [325 posts]
22nd December 2011 - 22:41

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found that 50-36 (a genuine SRAM chainring too !!) is an
even nicer combo with a 12-26 out back Smile

still on the 3rd switch-back of Bwlch !

posted by therevokid [730 posts]
24th December 2011 - 17:36

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My main beef with compacts is the fact that you end up in 50 all the time, as the 34 is useless unless climbing steep stuff.
Whilst the 39 on a standard makes a nice general purpose gear.
Just about to convert my training bike from 53/39 & 11-25 to 53/38 & 12-27.

posted by oldgit [27 posts]
31st December 2011 - 7:59

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Triples are for the old, heavy, injured? You cheeky b******s Angry I ride a triple as I live in Devon and like the slick shift you get on a straight through block...A couple of hours ago I left my companions for standing on a 1 in 5 because I can change gear comfortably whilst out of the saddle (because of the close ratio) and they cannot. I love the sound of their clunking gears. Triples are superb in the hilly country round here the old, heavy injured need not apply; or stick to the Tarka trail of course!

posted by SideBurn [838 posts]
31st December 2011 - 19:48

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