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PostPosted: Thu May 15, 2014 4:42 am 
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Joined: Tue Dec 27, 2011 2:19 pm
Posts: 606
I couldn't find a relevant topic in the search, so I guess I"ll make a new one...

I've been on standard 53-39 cranks forever. I ride in an area with some long false flats and a few short punchy hills. I'm talking 2-4% grade for 3-4 miles being the longest or a 10-16% grade for under 200 yards, being the steepest. my current setup is standard on super record 12-27 cassette. my drivetrain is pretty worn down and I"m going to replace a cassette, chain, and I started thinking about the crank as well (It's a rotor 10 speed crank which has a loss in shifting speed/precision with the 11sp campy setup since chainring spacing is different than on campy 11sp cranks, besides I can lose a ton of weight moving to the new Over-torque crank)

When I run the gear calculators I see that with a compact crank and a smaller cassette I can get basically my same range while shedding weight in the cassette and possibly the crank as well.

Has anyone else made this move? I would only do this on my Cervelo R5 (5.9 kilos already) I'd leave the rest of the fleet with the standard crank.

If it matters I typically ride with groups at 22mph (35kph) on flats (+ or - wind, rain, motivation) and pedal at a cadence between 90-105. I don't race, but I do like ultralight stuff (like everyone else here)

Feel free to tell me I'm nuts... my wife would appreciate the reinforcement!

Thanks!


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PostPosted: Thu May 15, 2014 5:55 am 
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Joined: Thu Jul 19, 2012 6:09 pm
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Location: Loveland, CO
From a purely theoretical analysis you also have to look at increased friction with the compact setup. Smaller chainring + smaller cassette = increased chain friction at the same bicycle speed. My guess is that any difference is so small that you won't notice it. How much weight savings are you looking at?

ps I run a compact setup with a 12x28 cassette not for weight savings but because I really need the low gears


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Posted: Thu May 15, 2014 5:55 am 


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PostPosted: Thu May 15, 2014 6:12 am 
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Being that this Weight Weenies. I'd say is you can save weight and it's still pleasurable to ride. Then go for it.

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PostPosted: Thu May 15, 2014 7:14 am 
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You'll save weight from having a shorter chain as well!

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PostPosted: Thu May 15, 2014 4:10 pm 
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Joined: Tue Dec 27, 2011 2:19 pm
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According to competitive cyclist (I believe their numbers more than manufacurers)

I'm going to drop about 120 grams from my Rotor 3D+ to a Campy Overtorque crank (it lists the same weight for standard or compact, which doesn't really make sense to me but I'm betting it's so new they haven't weighed them all yet)

But I will for sure drop 30+ grams going from a 12-27 cassette to a 11-25 cassette, and a little more if I drop to a 11-23. (This is in the chorus line, steel is real when it comes to cassettes and I'd rather have a $150 cassette that lasts a season or two than a $500 cassette that lasts 1/4th as long)

and maybe another gram or two in chain shortening...

so going compact would be a net 30-40 gram loss over staying standard? (not really concerned about price/ gram since I will be upgrading this stuff anyway)

anyone else bounce between standard and compact on different bikes?


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PostPosted: Thu May 15, 2014 4:28 pm 
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Joined: Fri Jan 31, 2014 4:54 pm
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39/27 is 1.44
53/12 is 4.42

When you bought 50-34 and 23-11 setup; ratio is 1.48
50/11 is 4.54.

So 50/11 is faster than 53/12.
34/23 is a bit harder than 39/27 so you can consider buying 25 cassette.

As a result;
You will have lighter components, shorter chain and closer ratios on cassette.
Biggest disadvantage is the look in my opinion. I really don't like the look of compact crank on road bikes.

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PostPosted: Thu May 15, 2014 4:38 pm 
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It wont be as much weight savings however you should also consider the so-called mid-compact being widely offered recently. I have been riding around southern Ohio (which has similar terrain to what you described) on my colnago with a mid compact and an 11-25 and it has been really nice! It consists of a 52/36 and if you are worried about under or over gearing it provides a really nice middle ground. You run it on a compact crank (110 BCD) like a 50/34 which is also nice because if you take a trip to the mountains or something you can switch down to a set of compact rings with a simple ring (and perhaps chain) swap unlike a standard 53/39.

Plus slight weight loss still :thumbup:

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PostPosted: Thu May 15, 2014 4:58 pm 
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Joined: Thu Jul 19, 2012 6:09 pm
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Location: Loveland, CO
Another benefit of going compact is that with a smaller big ring it allows you to stay in the big ring longer as the road tilts up. This is an important and often overlooked psychological advantage, haha. Joking aside this advantage is real on rollies as there would be less front shifting going on....a real benefit. Go for it!


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PostPosted: Thu May 15, 2014 5:41 pm 
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Does anyone have numbers for the friction loss between 11t and 12t, which to the best of my knowledge is pretty big, but haven't got actual reliable % numbers, and also numbers for friction loss between 53 and 50? Can't imagine that being huge, but still it is absolutely there...

There is a reason we've seen some bikes with chainrings just barely clearing the ground for world record attempts.

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PostPosted: Thu May 15, 2014 6:48 pm 
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Location: Santa Cruz, California, USA
difference from 11t to 12t: .3 watts @ 200w input.

http://djconnel.blogspot.com/2010/01/dr ... erent.html


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PostPosted: Thu May 15, 2014 8:16 pm 
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Joined: Fri May 25, 2007 6:43 pm
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And depending on the terrain and your fitness you may save *some* power by getting a slightly better chainline.

Probably about the range order of magnitude as you lose by going to smaller cassette and chainrings........

(I switched to compact due to a lack of fitness and excessive eating, and to be quite honest, I'm pretty sure the next new bike will start off with compact, and probably stay there. I can get up mountains, and get down them again with no noticeable issues. Except the weedy legs and fat gut)


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PostPosted: Fri May 16, 2014 1:00 pm 
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DMF wrote:
Does anyone have numbers for the friction loss between 11t and 12t, which to the best of my knowledge is pretty big, but haven't got actual reliable % numbers, and also numbers for friction loss between 53 and 50? Can't imagine that being huge, but still it is absolutely there...

There is a reason we've seen some bikes with chainrings just barely clearing the ground for world record attempts.



I have heard this and thank you to others for the response, but my time in the highest gear is usually soft pedaling on big descents. I'm more of a spinner than a grinder so this one is pretty far down the list of things to consider on my end.

I went to my LBS yesterday and talked to my wrench, we dug in the spacer box and found enough to make it work on my BBright Cervelo R5 and ordered a Campagnolo Over Torque Ultra Comp yesterday at my, should be in next week, I'll get full bike weights before and after when it gets installed. I also had him set aside some higher end bearings, right now I'm on a SRAM FORCE level bearing, so I'm going to toss in a SRAM RED bearing while we have it all apart.


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PostPosted: Fri May 16, 2014 3:33 pm 
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Joined: Thu Mar 20, 2008 3:03 am
Posts: 620
Location: nyc
I love the insanity of this premise@!!!

True WW post here....I miss the good old days...

Maybe try cutting-off every other chainring tooth too, save the weight there!

I've decided to cut off a couple of toes and pull out the rest of my toenails...

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PostPosted: Sat May 17, 2014 7:31 pm 
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Go singlespeed, save even more.


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PostPosted: Sat May 17, 2014 9:06 pm 
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Joined: Thu Jul 19, 2012 6:09 pm
Posts: 120
Location: Loveland, CO
Although the crank doesn't spin very fast we're talking about rotational weight savings here. When I dropped 186g. by upgrading the crank I noticed the weight savings immediately after leaving the driveway on a level road.


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Posted: Sat May 17, 2014 9:06 pm 


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