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Old 09-21-08, 03:29 PM   #1
cyclinfool
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Compact convert

Today was the trial ride of the new group on my Simoncini. The triple Veloce group was about 12 years old with about 15K miles on it, it still worked fine but I came into a little bike money, enough to pay for a 10 spd Chorus upgrade. I finished the build yesterday, adjusted the drive train as best as I could and took it for a spin. I really like the compact crank set with the 10spd cassett, I think it will be easy to stay in the 50 ring for most riding and drop to the 34 ring for the climbs. The pedal feel is really smooth. I don't have the gears adjusted quite right - I am getting a little skipping when in the 34/23,24,25 & climbing - but I think I'll get that out with a little more fiddling. I can't wait for next weekends century. I think I am a compact convert! I'll still keep the triple on the Tarmac because thats my climber and it needs the range only a 54/39/30 triple can give but for a long distance rider, the compact is a great alternative. Since the steel Simoncini is my distance bike - I am more than pleased

The Simoncini now sports a 50/34 crank & 25/11 Cassett. It now has a great top end and an adequate low end.
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Old 09-21-08, 07:17 PM   #2
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I enjoy having both my 50/34 and my 53/39......but definitely need the compact when riding in the mountains. I'm glad your initial impression was positive.
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Old 09-22-08, 04:22 AM   #3
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This is also my impression of the compact. I treat it more like a dual range crankset. Low range, most of the gears for climbing or slow speed stuff. High range for most open road riding. Cross chaining is not much of a problem as both chain rings are relatively close to the center of the cassette.

That may be the other big advantage of the double, just about full use of the cassette from either chainwheel in addition to easier shifting.
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Old 09-22-08, 06:49 AM   #4
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Get a cassette with a 27 or 28 cog on it, and you'll have virtually the same low end as your triple, within one or two gear inches.
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Old 09-22-08, 10:42 AM   #5
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Have compacts on my Hill Bike and the Distance bike. Have a triple on the OCR and I never got out of the 42- except downhills. The compact just has better gears for the hills and the flat.
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Old 09-22-08, 06:24 PM   #6
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Get a cassette with a 27 or 28 cog on it, and you'll have virtually the same low end as your triple, within one or two gear inches.
Yep - I did a lot of figureing before I settled on the 11/25. Since I never dropped into the 32 on this bike except for a few very steep hills I figured the 34/25 ratio will do me just fine. The low ratio on the bike was 1.28 where as now it is 1.36. The low gear on the Tarmac is 1.2 and there is only one hill I climb where I need that gear not to mention the added stiffness and 5lbs less weight the Tarmac brings.

Worked on the adjustment tonight - I have gotten it better but it seems to want to skip the 4th or 5th ring in the cassett, I have teh skipping out of it but can't seem to find a spot where all the gears shift smooth. It does better in the big ring than in the small ring. I think I will ride it some more and see if it settles in.
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Old 09-23-08, 06:35 AM   #7
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Yep - I did a lot of figureing before I settled on the 11/25. Since I never dropped into the 32 on this bike except for a few very steep hills I figured the 34/25 ratio will do me just fine. The low ratio on the bike was 1.28 where as now it is 1.36. The low gear on the Tarmac is 1.2 and there is only one hill I climb where I need that gear not to mention the added stiffness and 5lbs less weight the Tarmac brings.

Worked on the adjustment tonight
- I have gotten it better but it seems to want to skip the 4th or 5th ring in the cassett, I have teh skipping out of it but can't seem to find a spot where all the gears shift smooth. It does better in the big ring than in the small ring. I think I will ride it some more and see if it settles in.
Are you using a new chain and cassette?
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Old 09-23-08, 10:44 AM   #8
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Everything is new, Chain, Cassett, Crank, derailuers, Brifters, cables.
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Old 09-23-08, 10:53 AM   #9
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Everything is new, Chain, Cassett, Crank, derailuers, Brifters, cables.
Could one of the cogs be in backwards? Maybe a bent dropout?
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Old 09-23-08, 10:57 AM   #10
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Originally Posted by cyclinfool View Post
Worked on the adjustment tonight - I have gotten it better but it seems to want to skip the 4th or 5th ring in the cassett, I have teh skipping out of it but can't seem to find a spot where all the gears shift smooth. It does better in the big ring than in the small ring. I think I will ride it some more and see if it settles in.
If it was my bike I'd check the derailleur hanger alignment. That'll sometimes make it skip a cog that way.
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Old 09-23-08, 11:07 AM   #11
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Could one of the cogs be in backwards? Maybe a bent dropout?


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If it was my bike I'd check the derailleur hanger alignment. That'll sometimes make it skip a cog that way.
Don't think it is a backwards cog as I kept the cassett mostly together when it went on - only the small ring slipped off and I had to put it back. The alignment may be the issue as I made no real attempt to align it when I bolded it up the the hanger. The hanger should be OK as the bike shifted perfectly with the old group. After working on it more last night I have it down to wanting to jump over one gear in the middle of the cassett, otherwise it is perfect - and it just does this when in the lower chain ring. I can tease it into this gear and it will stay but when moving a full click either up or down it will jump over this cog. The problem can be moved up or down a cog but I seem to have one that is not quite right.

Anyway I will check the alignment more carefully - I think it will just take some patience. I plan to ride a century on it this weekend if the weather holds - even as it is now I will have no problem riding it and running it in might help it.
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Old 09-23-08, 11:10 AM   #12
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Make sure that you have the spacers in the right sequence. I was in a hurry once and got them off a little and had the same problem.
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Old 09-23-08, 11:37 AM   #13
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I remember Frank Berto recomending compact, small tooth count drivetrains back in the early 1980s. He's reasoning at the time was it saves grams.

Some twenty years later, Mr. Berto did a drive train efficiency test with Dr. Chester Kyle (here, beginning on page three). They rediscovered - and empirically measured - some 100 year old knowlege about reducing tooth counts: the smaller the cogs, the lower the efficiency. Through most of the range used by cycle gear trains, the degradation is negilgible, but once the number of teeth drops under the mid-teens, it really starts to go south. A 34/11 is in the neighborhood of 10% less efficient than a 52/17 - a huge difference compared to the small amount of weight lost.

I see your drivetrain has an impressive 123 inch top gear. At 120rpm, that would deliver ~44 mph. As I said, impressive.

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Old 09-23-08, 12:16 PM   #14
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^^^^For some reason I can't get this to download past about page 3. I have to try again at home. Looks like an interesting article. I had always assumed that a roller chain drive lost very little turning corners.

Edit: for some reason I can't get this page to download beyond about 1/2 meg........then it hangs.
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Old 09-23-08, 12:42 PM   #15
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I remember Frank Berto recomending compact, small tooth count drivetrains back in the early 1980s. He's reasoning at the time was it saves grams.

Some twenty years later, Mr. Berto did a drive train efficiency test with Dr. Chester Kyle (here, beginning on page three). They rediscovered - and empirically measured - some 100 year old knowlege about reducing tooth counts: the smaller the cogs, the lower the efficiency. Through most of the range used by cycle gear trains, the degradation is negilgible, but once the number of teeth drops under the mid-teens, it really starts to go south. A 34/11 is in the neighborhood of 10% less efficient than a 52/17 - a huge difference compared to the small amount of weight lost.

I see your drivetrain has an impressive 123 inch top gear. At 120rpm, that would deliver ~44 mph. As I said, impressive.

Best,
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Since my normal RPM ranges from 80-90 that gives me a top speed in the low 30's which is correct. Infact Sunday when I had it out I was sprinting next to another rider and we were doing around 28 on the flat. It has more top end than I think i will reasonably use except when on the down grades trying to make up ground when having gotten dropped by the group on the upgrades...

As far as efficiency is concerned, I agree that the more the chain has to roll the more loss there will be, now is it significant compared to the losses in everywhere else in the system including the wind resistance when you are in the higher gears is the real question. One should always attack the nail which sticks up the highest first.
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Old 10-05-08, 06:45 PM   #16
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Finally found the problem here - the rear derailluer cable was on the wrong side of teh cable clamp and that little difference messed up the amount each click on the brifter moved the derailluer enough to cause it to skip one cog in the cassett. Once I moved it to the other side it shifted perfectly.
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