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Compact Double ?

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Old 07-28-06, 10:15 AM
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Txtigah
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Compact Double ?

I have come to the conclusion that I really don't understand how this compact double really works. Does anyone know of a website that offers a tutorial or if someone could explain this half shifting business. Any help would be appreciated.

Thanks!

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Old 07-28-06, 10:34 AM
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A compact double does not offer any half shifting. It is more or less a happy medium between a triple which has some really low gearing on the smallest front ring and a standard double that does not go near as low as a triple but does go as high as the triple on largest ring.
The compact offers you some lower gearing on the small front ring so climbing will be easier than a standard double.
The large ring is slightly smaller than a standard double large ring so you will lose some of the higher gearing but not much.
What does your bike have now for a drivetrain, what type of riding do you do (Hilly, flat, mountains)? Are you looking to switch or get a bike with a compact double?
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Old 07-28-06, 10:41 AM
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There is no doubt about the fact that a compact double is a compromise. It is difficult to get the percise gearing one might find perfect, in terms of smooth jumps between the large and small chainring. Most folks I know simply stay on the large chainring as long as possible and then drop down to the smaller one when they need the lower gears. For me this means I functionally have eight gears on the large chainring (I never go to the largest rear cog while on the large chainring... can't keep the chain from rubbing). I also have four functional gears on the small chainring (the four largest cogs). Hence, I find that 98% of my riding is done with just 12 gear combinations. For me this is a compromise I gladly make in lieu of a tripple.
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Old 07-28-06, 10:43 AM
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Originally Posted by NOS88
There is no doubt about the fact that a compact double is a compromise. It is difficult to get the percise gearing one might find perfect, in terms of smooth jumps between the large and small chainring. Most folks I know simply stay on the large chainring as long as possible and then drop down to the smaller one when they need the lower gears. For me this means I functionally have eight gears on the large chainring (I never go to the largest rear cog while on the large chainring... can't keep the chain from rubbing). I also have four functional gears on the small chainring (the four largest cogs). Hence, I find that 98% of my riding is done with just 12 gear combinations. For me this is a compromise I gladly make in lieu of a tripple.
Same here, just enough gears to cover all my riding conditions comfortably. Good post.
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Old 07-28-06, 11:39 AM
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Originally Posted by Txtigah
I have come to the conclusion that I really don't understand how this compact double really works. Does anyone know of a website that offers a tutorial or if someone could explain this half shifting business. Any help would be appreciated.
Thanks!
I Believe Floyd Is Innocent!
not being snitty, but BF has a mtn of great info, from tech to personal notes, if you do a 'search' here 'compact crank', you'll come up with tons of really valuable insight on the option/options. BF certainly helped me decide, in this respect.
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Old 07-28-06, 11:45 AM
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I'm also a compact crank convert from a triple. My old gearing on the triple was a 52/42/30 and I was running a 12/27 rear cassette. My new setup on the compact is a 50/34 crank and I run either a 12/25, 12/27 or even a 11/34 cassette depending on the terrain. The 12/27 is probably the best compromise for all conditions. With the 11/34 I actually have a wider range of gears than with the triple-especially on the low end.

With the 50/34 I've shaved some weight off the bike and feel like I'm using a larger percentage of the gears. I did have to change the rear derailluer to a mountain bike rear der to go with the 11/34 but it is very welcome on long climbs where the slope or grade is 10% or more.

You do lose a little gearing on the high end, by moving from a 52 or 53 to a 50 (or harder pedaling) but for me that is a low percentage of the time when I really needed that very hardest combination.

The FSA (lots of various choices of models in the FSA line) is a very popular, potentially lightweight and nice looking compact crank. However, the best shifting compact right now is probably the Shimano R700. It is slightly heavier than some of the carbon FSA's but from my experience you don't have the chain drops that you might have with a FSA when shifting from the 50 to a 34.

By the way, you can also get a 36 chain ring instead of a 34 if those gear inches suit you better.

I've also found like the others that usually I'm spinning more in the 50 than the 34-which probably is a substitute for being in the middle chain ring before.

Hope this helps.
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Old 07-28-06, 11:52 AM
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As far as top end is concerned, I find that with today's 11/12T cogs, the 53 ring is simply too large to push, even on descents. A 50 or even a 48 ring gives me plenty of top end.
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Old 07-28-06, 11:56 AM
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If you currently have a double, and are looking for more usable gears on the large ring, then you could just change the big ring from a 53 to a 50 for around $30-$40. You also can change your rear cassette to a 12-27 to give you more range on both the large and small front rings. Lots of options depending on what you want to accomplish.
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Old 07-28-06, 12:44 PM
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I'm running the 50-34 FSA with a 11-23, here in central il i hardly use the 34, but when i was in southern il
the 34 worked out great. i dont have any chain drop problems, i do have to let up on pressure slightly when shifting to large ring for it to shift.
the 50-11 is a larger gear than the 53-12 also

karl

here's a gearing link
http://www.fullspeedahead.com/downlo...ut%20chart.xls

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Old 07-28-06, 01:12 PM
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I have a bike with a double and while I was at the bike shop they were talking half shifting and quite honeltly i was lost.
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Old 07-28-06, 01:22 PM
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half shift

check this, i believe this is half shifting, i call it trimming
http://www.bikeforums.net/attachment...4&d=1154050825

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Old 07-28-06, 02:20 PM
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Now I understand what is meant by half shifting. I have always know it as trimming. I am not sure how it works on the Campy but on Shimano it is pretty straightforward. If you are using STI levers the trim will help eliminate the chain from rubbing on the front derailleur.
For example: you are on the small cog on the back cassette and the big ring in the front. All is fine, no rubbing of the chain on the front derailleur. Now as you shift the back derailleur to a larger cassettes the chain may begin to rub on the inside of the front derailleur due to the angle the chain with respect to the front ring. If you give the front deraillur(smaller black lever) one small click it will move the derailleur slightly to the left so you do not get this rubbing. If you click the lever again it will move the front derailler enough to shift to the lower ring in the front.
So basically it is a way of moving the front derailleur enough to make a small adjustment so the chain will not rub. Once you figure it out and learn to use it, it will be second nature. Until then it is just plain frustrating.
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Old 07-28-06, 03:58 PM
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Many moons ago -we did not have indexed shifters in that one click and we change to the next gear. It used to be friction shifters. You just moved the lever till you changed gear and then stopped. I was lucky in that I had XT topshifters on my Kona and these were indexed but by flipping a tag- you could change to friction shifting. Index shifting has improved over the years, but there are still times when I wish for that old style friction shifting to compensate for the cable stretch that comes on in the middle of a hill.
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Old 07-28-06, 04:01 PM
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My "current" Shimano downtube shifter has that switching tag.
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Old 07-28-06, 05:16 PM
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My bar end shifters also have that little switch to go between index and friction but only on the rear.
The front is friction and I do not mind it. Just move it a little bit one way or the other.
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Old 07-28-06, 05:52 PM
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Originally Posted by NOS88
Most folks I know simply stay on the large chainring as long as possible and then drop down to the smaller one when they need the lower gears. Hence, I find that 98% of my riding is done with just 12 gear combinations.
I'm a little different in that I generally stay on the small chainring (about 80% of the time) and only move to the large when things gets quicker (>35kph). It's probably a reflection of my highish cadence - normal cadence for me is between 95-100 rpm and it doesn't seem to bother me too much if it climbs up to 105. The bulk of my riding would be done in only 5 or 6 gear combinations.

I don't find I miss out on the top end. If I push hard in the top ring with the small cog I'm seeing around 60 kph and my nerve is giving out before my legs

Having said all that, the compact wasn't even a consideration when I bought the bike - it was just standard equipment and seems to work just fine.

// kak
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Old 07-30-06, 01:31 PM
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My two road bikes have friction-only Suntour bar-end shifters. My MTB has friction-only Suntour top shifters. The tandem has Shimano indexed bar-end shifters with friction option. None of these have indexing on the front and it is so much easier to use and to set up than the newer shifters with indexing on front. If the chain rubs the front derailleur you just move the lever until it stops rubbing. So simple.

I have just switched my main road bike from 30-40-50 Campy triple to 34-50 compact double. I had a Sugino XD triple crank (110 BCD) with steel rings, so I removed the small ring and replaced the middle and large rings with aluminum Sugino rings. I used a 113 spindle bottom bracket (had been using a 118 on this crank as a triple on another bike. I kept the Campy triple front and long cage rear derailleurs as I figured they could handle the larger steps between the front rings.

After one short ride I'm very pleased with the way it turned out. My big ring is the same 50 teeth as before and the 34 small is a good compromise of the 30 and 40 I had. I'll probably use the big ring a little more, but I still have several useable gears on the small ring. I've lost a lot of weight and gained a lot of strength in the past year, so I was almost never using the small ring anymore.
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Old 07-30-06, 02:07 PM
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I have never heard of half shifting but suspect that is what I call the trimming function. There is a method of gearing called half-step gearing where the two chainrings are relatively close to each other and the rear cogset splits the difference so that you get evenly spaced gearing jumps by alternating your shifting between front and rear. It seems to have fallen from favor. For the compact system, I have a 50-36 on my commuter and a 50-34 on another bike. Compared to the 53-39, I find the 50-34 considerably more useful. I do not miss the 53 at all. ymmv
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Old 07-30-06, 02:52 PM
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On my ride today- I started to use a few more gears than I normally would and I had the front Derailler Rubbing the chain in certain gears on the rear cassette. Thought about your double shifting and suddenly realised that I could cure the rubbing. I have Sora changers on the giant and to shift the front derailler you just push once- but this one shift is actually moving the derailler twice. With a full swing of the lever- I will change smoothly from one ring to the next. However- If I just push the lever partway- it does not fully move the chain to the next ring. So As I found out- small chainring on the front and biggest ring on the rear cassette is fine. Then as I change up to the smaller rear ring- I was getting the chain rub on the Front derailler. Just a touch on the lever and no chain rub.
Hadn't really thought about it, but the half change is there. Funny how technology has moved on to cure a problem that never used to exist with friction shifters.
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Old 07-31-06, 08:25 PM
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I've also got a compact crank on my Lemond. I went smaller on the big ring, with a 46/34 combo and either 13-26 or 12-32 on the cassette. There are times when I spin out on downhills, but I can also power over some rolling hills that aren't too steep in the 46T ring. I'm almost always on the 46 on the flats and gradual rises. On hilly rides, the 34-32 combo gives me a nice low gear for the steeps. Before I had compact, I ran a 52/42/30 triple with 13-26 in back. I think the triple crank is one of the nicest innovations they've come up with in years.

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Old 08-01-06, 03:29 AM
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I cannot imagine riding without my 53T chainring.
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Old 08-01-06, 08:00 AM
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Here is a chart of gear inches for several top gear options. smallest rear cogs are running down the left side, largest chainrings run across the top. The intersection of the rows and columns shows the gear inches for that combination.

46 48 50 52 53

11 113 118 123 128 130
12 104 108 113 117 119
13 96 100 104 108 110

My current highest gear is a 13x50 or 104 inches. With a 12 cog I can get 113 inches which is all I can imagine ever needing. A 11x46 combination would acheive the same high gear. 11x48 is about the same as 12x53. 11x50 is higher than 12x53. If you can push a 11x53 gear, we need to evaluate your testosterone level for possible violations
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Old 08-01-06, 08:45 AM
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Originally Posted by BluesDawg
Here is a chart of gear inches for several top gear options. smallest rear cogs are running down the left side, largest chainrings run across the top. The intersection of the rows and columns shows the gear inches for that combination.

46 48 50 52 53

11 113 118 123 128 130
12 104 108 113 117 119
13 96 100 104 108 110

My current highest gear is a 13x50 or 104 inches. With a 12 cog I can get 113 inches which is all I can imagine ever needing. A 11x46 combination would acheive the same high gear. 11x48 is about the same as 12x53. 11x50 is higher than 12x53. If you can push a 11x53 gear, we need to evaluate your testosterone level for possible violations
I just put a 53/39 on my Madone and I've found I can easily push the 53/12 (12/27 cassette).......although it has to be going down a descent of at least 3-4%!!! What was I thinking?????
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Old 08-01-06, 09:05 AM
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My bike came with an Ultegra crank (53/39 chainrings) and 12-25 cassette, but since I'm old and many of the bike club rides are hilly, I've installed a Shimano R700 compact crank. I have 2 Ultegra cassettes; 11-23 and 12-25. I've combined them into an 11-25 cassette (11,12,13,14,15,17,19,21,23,25) so that I have higher top end and lower low end compared to how the bike came stocked. There should be a miniscule amount of weight savings realized as well.

One tip if you decided to run an 11-25 cassette--remember to use the locking ring that came with the 11. The one for the 12 is too big and -may not- allow the cogs to be tightened down properly and -will not- let the chain seat properly in the teeth of the 11T cog.

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