Front chainrings (compact vs mid-comp vs standard)

Discuss light weight issues concerning road bikes & parts.
AJS914
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Joined: Tue Jan 28, 2014 6:52 pm

by AJS914

Well, when I raced 25 years ago our big gear was a 53-12. I'd usually start my sprint in a 53-14 and finish in the 53-13 or the 12 if there was a tail wind.

In any case, it's too bad Campagnolo isn't making a 12-29 or 12-32 12-speed cassette. For me that would be perfect with a 52x36. These cassettes that start with an 11 are the primary reason I have zero lust for 12 speed. It gives me one extra gear I never needed or wanted.

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Calnago
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by Calnago

I have Campy cassettes in 12/25, 12/27 and 12/29. But yes, they stopped making them and I would bet anything its not because they weren’t useful for many, but rather, everyone wanted the 11... not because they could necessarily push the 11 effectively, but because it was cool. After all, what “sprinter” would ride a bike without that 53/11 combo. I wouldn’t, and I’m a sprinter. “Right mom?... I’m a sprinter right?”
“Yes Calvin, you’re a sprinter, now please take out the garbage.”
Market trends and demand.
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by Weenie


wobbly
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by wobbly

My gear sizing spreadsheet now has the Shimano 14-28 highlighted with 52-36
This would mean the small chainring for uphills with nice gaps and the big chainring for the flats for my modest power output.
No-one ever said the smallest gear was too small :wink:

Just need to switch back to Shimano....

AJS914
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by AJS914

My theory is that the Compact crank is killing the 12-xx cassette. Most everybody I know switched to a compact once they were available. It was great to have the extra climbing gears but it's easy to spin out in a 50x12 so everybody wanted the 11.

I'm still hoping that Campagnolo will make 12-29 and 12-32 12-speed cassettes in the future.

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Calnago
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by Calnago

^Same thing essentially. Everyone wants that go fast gear. So with a 50/11 not too much is given up to the 53/11 big boy gear, and is actually even bigger than the 53/12, not by much but it is. Thing I dislike about the compact 50/34 is not just the excessive back and forth compared to either the 36/52 or 39/53, but it is also the combo that is most likely to drop a chain on the inside. The physical distance the chain must drop from the 50 to the 34 is the largest of the 3 combos. It was little wonder when the compact became popular that all of a sudden there were way more chain drops. I remember on a sponsored ride with tons of people I seemed to be constantly stopping to help people get their dropped chain back on. And guess what, that was the main mechanical takeaway from the day... these compact cranks sure do drop a lot of chains. Then came the rise of the chain catchers which help immensely.
The other thing is that people talk like they have to end up in the next cog to be in the next gear. I rarely shift the front without simultaneous shifting the rear 1,2 or 3 cogs at a time. It’s instant and second nature. With today’s double cranks and close ratio cassettes there is a lot of overlap and “in between” gears. And that isn’t a bad thing. I am never wanting for a gear that I can’t get to instantly. Simultaneous front/rear shifting also keeps the chain at a pretty good chain line reserving but not limiting the outer two cogs at either end of the cassette for the extreme situations of really hard climbing or really fast sprinting. This is something that Campy mechanical excels at under an experienced user. Can’t do that nearly as efficiently with any of the other groups and certainly not with a 1x system. I’ve gotta say, I’m pretty happy with the gearing choices available for road bikes these days.
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spdntrxi
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by spdntrxi

50/34... did not work for me often enough (it depends on who I ride with)... 52/34 is shifting pretty good for me right now ... so I might just stay with it. 48/32 will go on the allroad bike soon.. (once my road bike is built). Road bike needs that 52t for sure.

ooo
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by ooo

Front shift chain drop distance:

32,3 mm 52-36T (radius=105-73 mm) - mid-compact
32,3 mm 50-34T (radius=101-69 mm) - compact

32,3 mm 48-32T (radius= 97-65 mm) - sub compact
32,3 mm 46-30T (radius= 93-61 mm) - sub compact
32,3 mm 48-32T (radius= 97-65 mm) - urban sram
28,3 mm 46-32T (radius= 93-65 mm) - urban shimano

28,3 mm 53-39T (radius=107-79 mm) - standard

26,3 mm 50-37T (radius=101-74 mm) - sram 2019
26,3 mm 48-35T (radius= 97-71 mm ) - sram 2019
26,2 mm 46-33T (radius= 93-67 mm ) - unknown

20,2 mm 46-36T (radius= 93-73 mm) - cx
16,2 mm 42-34T (radius= 85-69 mm) - cx women
14,1 mm 46-39T (radius= 93-79 mm) - cx top
'

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Calnago
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by Calnago

@ooo: Ha. Well done. I’ll take your word for it. I know when I actually measured the distance I just did it with a ruler and was comparing the compact at the time 34/50 with the standard cranks 39/53. I thought I had checked the 36/52 as well but maybe not as they weren’t even out yet. The only reason I came up with for the inordinate number of chain drops with compact cranks was that it was easier for the chain to “miss” the landing mark the further it had to fall. Maybe it has something to do with the tighter radius as well. But it just seems that compacts would be more subject to chain drop than either the 36/52 or 39/53. But for sure, 39/53 just never experienced frequency of chain drops of 34/50, well... except for Andy Schleck.
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alcatraz
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by alcatraz

Seems there is something else apart from the tooth difference that dictates a feasible setup or not.

You don't see 16t difference mtb or cx cranks.

Maybe a theory could be that as the small ring gets smaller the same drop in teeth will start to cause more chaindrops. There's simply less to grab on to. Maybe the rd cage tension also plays a role.

The killer is obviously the upshift. I guess shimano rings are better with that and they can handle 52/34 pretty well. Some can't even handle standard 16t spacing wihout dropping chans.

blaugrana
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by blaugrana

ooo wrote:
Thu Dec 06, 2018 12:43 am
Front shift chain drop distance:

32,3 mm 52-36T (radius=105-73 mm) - mid-compact
32,3 mm 50-34T (radius=101-69 mm) - compact

32,3 mm 48-32T (radius= 97-65 mm) - sub compact
32,3 mm 46-30T (radius= 93-61 mm) - sub compact
32,3 mm 48-32T (radius= 97-65 mm) - urban sram
28,3 mm 46-32T (radius= 93-65 mm) - urban shimano

28,3 mm 53-39T (radius=107-79 mm) - standard

26,3 mm 50-37T (radius=101-74 mm) - sram 2019
26,3 mm 48-35T (radius= 97-71 mm ) - sram 2019
26,2 mm 46-33T (radius= 93-67 mm ) - unknown

20,2 mm 46-36T (radius= 93-73 mm) - cx
16,2 mm 42-34T (radius= 85-69 mm) - cx women
14,1 mm 46-39T (radius= 93-79 mm) - cx top
Yes, and this is not only true for these examples, but for any size of chainrings, if the tooth difference is the same, their size difference will be the same as well. This is because the chain drop distance is 2*pi*l, where l is the length of the extra teeth on the big ring compared to the small one.

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Calnago
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by Calnago

blaugrana wrote: Yes, and this is not only true for these examples, but for any size of chainrings, if the tooth difference is the same, their size difference will be the same as well. This is because the chain drop distance is 2*pi*l, where l is the length of the extra teeth on the big ring compared to the small one.
Now there’s a good bit of math right there, and all the proof I need to determine which combos have the largest drop just from the tooth differential. Thanks, wasn’t sure if it was that simple and thus I got out the ruler long ago. Ok, so the drop is the same on the 36/52 and the 34/50, yet it certainly seems the likelihood of chain drop to the inside is much higher on the 34/50 (from experience and yes, it certainly could have been setup issues as well). Just curious now I suppose, and it’s probably moot anyway considering most people run chain catchers these days. But I think, as was mentioned already I beiieve, the larger the radius is on the smaller ring, the easier it is for the chain to catch a tooth or two as it drops down from the big ring. At least that would make sense to me.
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basilic
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Location: Geneva, Switzerland

by basilic

blaugrana, I think you flipped the variables, it's length=2pi*drop
With the number of aging wannabes out there buying bike stuff I don't understand why there isn't a line of 12-x and 13-x cassettes. I'd buy those.

Marin
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Location: Vienna Austria

by Marin

The solution is called 1x

3Pio
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by 3Pio

Calnago wrote:
Wed Dec 05, 2018 9:30 pm
I have Campy cassettes in 12/25, 12/27 and 12/29. But yes, they stopped making them and I would bet anything its not because they weren’t useful for many, but rather, everyone wanted the 11... not because they could necessarily push the 11 effectively, but because it was cool. After all, what “sprinter” would ride a bike without that 53/11 combo. I wouldn’t, and I’m a sprinter. “Right mom?... I’m a sprinter right?”
“Yes Calvin, you’re a sprinter, now please take out the garbage.”
Market trends and demand.

After some experimenting 52/36 in the front with 12-29 (I choose Chorus Version for longevity) in the back is my personal choice for terrain i ride (plenty of steep climbing, and every ride is minimum 500m climb up to 2000m (gradient from 5% up to 20%). But it's not just climbing.. On our very often riden route there is 1250 m climb in 120 km ride, when there is like 20 km flat part, then steep climb, then rolling hills....So also a lot of variety...So 12-29 perfect...

Im very dissapointed if Campy really stop producing 12-29.. Are they officialy stopped making 12-29? And since when? If this is the case, to know to order few 12-29 while i can see them on stock...

blaugrana
Posts: 65
Joined: Wed May 24, 2017 9:49 pm

by blaugrana

Calnago wrote:
Thu Dec 06, 2018 3:37 am
Ok, so the drop is the same on the 36/52 and the 34/50, yet it certainly seems the likelihood of chain drop to the inside is much higher on the 34/50 (from experience and yes, it certainly could have been setup issues as well). Just curious now I suppose, and it’s probably moot anyway considering most people run chain catchers these days. But I think, as was mentioned already I beiieve, the larger the radius is on the smaller ring, the easier it is for the chain to catch a tooth or two as it drops down from the big ring. At least that would make sense to me.
Yes, that only means that the distance is the same, but there are many other variables at play that could make a chain more or less likely to drop. I guess the main thing to consider is that on bigger chainrings the chain still have more teeth engaged to the big ring while it's trying to engage the small, making it less likely to fall off. Intuitively, on a ridiculously huge set of chainrings with the same gap as a compact (say 216 and 200 teeth) it would be much more difficult to drop the chain. Whether the difference when going from compact to mid-compact is signifficant is a completely different matter, but it certainly could be.

basilic wrote:
Thu Dec 06, 2018 6:32 am
blaugrana, I think you flipped the variables, it's length=2pi*drop
With the number of aging wannabes out there buying bike stuff I don't understand why there isn't a line of 12-x and 13-x cassettes. I'd buy those.
Yes, you are right, I should have double checked before posting. In any case, the main point is that the relation is linear, so the same teeth difference results in the same drop distance no matter the size.

by Weenie


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