Front chainrings (compact vs mid-comp vs standard)

Discuss light weight issues concerning road bikes & parts.
wintershade
Posts: 239
Joined: Mon Apr 16, 2018 7:12 pm
Location: San Francisco, CA

by wintershade

Hi all --

I'm having some difficulty choosing the right front chain rings. I realize this is highly subjective based on FTP/weight, terrain, preferred cadence, etc. but I'm curious how others have landed on what they prefer. My situation is complicated by the fact that I'm putting Campy 12-speed on my next acquisition (a true work of art which will be on display at NAHBS and will post a build thread in about 3 months when it's done), but the addtional 12th gear is complicating my decision making.

About me: 3.5 watt/kg. Road riding is generally long weekend miles, chasing Strava PRs and the occasional sportive/fondo, with my only racing being Ironman/triathlon. Riding hilly (but not mountainous) terrain with the typical long rides I do averaging ~750 ft per 10 miles.

Most of the threads I've seen online about chainring selection focus on having a high gear to avoid spinning out. That's not my concern. I'm not worried about sprint-finishes and when descending fast I'd rather tuck aero. For me, it's more about wanting a more efficient chainline and fewer front shifts. I have 5 bikes, but my main ones are:

"Climbing" road bike with Record compact and 12-29 cassette, I find I spend a lot of time either cross-chaining (especially since for flatter sections I have a tendnecy to leave it on the 50T big ring) or do a lot of front shifting. I like the 12-29 better than the 11-29 because I need that 16T cog.

"TT race bike" with DA Di2 mid-compact and 11-28, I find I do a lot less front shifting, but I'm probably underutilizing the big ring and although 36/28 is fine for a race bike, I'd want a wider range for more leisurely riding on my "sunny day" dream bike.

Anyhow, so the question is -- do I go with a compact + 11-29, or mid-compact with 11-32.

With new(ish) Super Record 12 -- The 32 looks pretty appealing.
11-29 Ratios: 11-12-13-14-15-16-17-19-21-23-26-29 (266g)
11-32 Ratios: 11-12-13-14-15-16-17-19-22-25-28-32 (270g) -- the spacing looks great to me, basicly I get a 11-28 SRAM 11 speed casette with an addiional bail-out 32T gear. The biggest advtantage I see is similarlity to my TT race bike (same gear with just an extra bailout gear for long rides or when I want to chill)

With the 34/50 and 11-29, my min/max gear ratios are 1.17 and 4.55
With the 36/52 and 11-32, I get 1.13 and 4.73.

The way I see these two combos is: 12-speed Campy is affording me a "free" 32 bailout gear with the mid-compact setup, or a free 11T with the compact (normally I'd run only a 12T, because I prefer the 16T to the 11T in the 11-speed casettes).

Sorry for the rambling post.

by Weenie


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Calnago
Posts: 8428
Joined: Sun Nov 07, 2010 9:14 pm

by Calnago

Personally, I'd go with the mid rings (36/52) and choose the cassette based solely on whether you think you need the 32 that much. I never liked the compact (34/50) for the exact reason you mention, found myself too often switching between big and small rings. I really like using standard chainrings (39/53) and think that provides the overall smoothest experience of all over the course of an entire ride. Like you, I also like a nice chaninline for the vast majority of any given ride. Chainline is something conveniently largely ignored by the 1x club, since you really need to make use of the entire cassette a lot more if you only have one chainring up front to work with. It's not something to be ignored as everything runs so much more efficiently with a good chainline. So, when I shift between rings up front, I'm almost always simiultaneously shifting the rear by 1, 2 or 3 cogs at the same time and end up pretty much exactly where I want to be. Remember, that mystical 16tooth arose out of a time when standard chainrings were, uh... standard (39/53). Cruising along in the 53 in a paceline often finds one wanting for that 53/16 combo. Go test it out, see what speed that is. But if you drop down to a 52 up front, then the cog that gets you closest to that same speed is the 15 (if still forced to choose between 15 and 17). If you go to a 50 up front, then the 15 cog is almost the same as a 53/16, but you have the issue of switching between front rings much more I find. Point is, once you leave the 53 ring at home, and opt for either the 52 or 50, then the mystical sweet cog becomes a lot closer to the 15 than the 16. Just a thought. But, and this is big... it's all moot with 12 cogs, because the spacing between the center cogs in the cassette can still be kept pretty tight, especially with two rings up front. You've got plenty to play with in that range. I wouldn't even sweat it. You can't really go wrong here, but for me the only way I'd go full compact is if I was going somewhere that I really thought I'd be in the small ring (34) the majority of the time.
Remember, we're still talking road bikes here I hope. Paved roads, not mountain goat type stuff. There are other bikes for that.
Last edited by Calnago on Tue Dec 04, 2018 2:26 am, edited 2 times in total.
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spdntrxi
Posts: 3013
Joined: Sat Jul 20, 2013 6:11 pm

by spdntrxi

For pure road 52/36 is hard to beat... combined with an 11/30 I'm pretty happy. Maybe 32 if I know the ride will have sustained 10% plus. I was tooling around with 50/34 but spinning out on some group rides I do and on the border of getting dropped... the 52 keeps me there with not much to spare.

AJS914
Posts: 3399
Joined: Tue Jan 28, 2014 6:52 pm

by AJS914

With the cassettes available for 12 speed, I think I'd just go with the 11-32 and the mid-compact.

wintershade
Posts: 239
Joined: Mon Apr 16, 2018 7:12 pm
Location: San Francisco, CA

by wintershade

Thanks guys, especially Calnago -- I can always count on you for a very thoughtful response. 52/36 with 11-32 it is. This combo feels like a really great reason for me to run 12 speed Campy (and I've been looking for one for a while). I get cassette range I need for long days in the hills with front rings that won't have me running sloppy chainlines or shifting all the time.

If I lived somewhere flatter or with shorter/more gradual climbs I'd be all over it for at least one bike, but after two overuse related knee surgeries I figure play it safe and keep and extra cog in reserve.

VirginiaWheeler
Posts: 6
Joined: Tue Dec 04, 2018 4:57 pm
Location: Mclean, VA

by VirginiaWheeler

I recently switched my big ring to a 48 and kept the little ring at a 34. I hate the 16t jump that compact and semi-compact gives you. I know there's great concern out there about "spinning out", but my 48x11 at 100rpm gives me 34mph. If necessary, I can maintain a cadence of 115rpm and that puts me near 40mph. Spinning our really isn't an issue. And with the smaller big ring, I have a clean chain line and I'm in the big ring a majority of the time. Just food for thought.
CAAD 11, Sram Red, Power2Max Type S, Zipp 404
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Svetty
Posts: 530
Joined: Thu Mar 26, 2009 11:06 pm
Location: Yorkshire - God's Own Country

by Svetty

I'd not rule out a 53-39 with the extra spread a 12 sprocket cassette offers. The smaller front gap makes front changes less disruptive and a 39-32 Will get up almost anything with 3.5W/Kgs.

wintershade
Posts: 239
Joined: Mon Apr 16, 2018 7:12 pm
Location: San Francisco, CA

by wintershade

Yeah, looking at a gear ratio chart, I guess a 39x32 high gear where I live isn't crazy and might actually help build some leg strength/power. That gives me a gear ratio of 1.22, which is actually better than the 36x29 (1.24) I generally ride now. That said, on longer, hilier rides with sustained climbing, I do sometimes find myself wishing I had just one more gear...

I guess the easiest way to test this out woudl be throw a 11-32 Potenza cassette and standard chainrings on my comuter road bike for a month or so and see how it goes. Unfortunately with Campy this simple test won't come cheap.

All that said, for my next build (code name "Rising Sun") I don't want a "reason" (other than weather or probability of a crash) to be a reason I choose a lesser stead. The mid-compact gives me more versatilty without the annoying qualities of a compact. My goal this year is to get FTP up to 4 watt/kg. Then I'd not hesitate. The question then becomes, would I not prefer going down to a 11-29 for tighter gearing at the back rather than smoother shifting at the front?

The good news is, with the new BCD designs, at least I can swap rings rather than needing a whole new $1000 chainset.

alcatraz
Posts: 2153
Joined: Mon Aug 29, 2016 11:19 am

by alcatraz

The 11-32t cassette is a clear winner as it has the intermediate gear(s) you said you needed.

It reduces the need for front shifting and prolongs the life of that groupset. We all get older, we go more sightseeing. Sooner or later you'll be in that 32t.

When choosing chainrings I like to simply look at time in each gear. What gear are you most likely going to spend more _time_ in? (as in seconds during a ride). A 34f+32r or a 52f+11r.

That will decide if you go mid-compact or compact. Easy as that.

Spinning out a big gear is usually not as common as feeling less than top and possibly needing that bailout gear. Climbing takes longer time than descending and so on. Personally I'd rather spin out a few seconds than to have to muscle my lowest gear at low cadence.

/a

basilic
Posts: 752
Joined: Wed Jan 05, 2011 8:05 am
Location: Geneva, Switzerland

by basilic

Before getting the 11-32 cassette, make sure you can live with the 19-22 gap, 16% smack in the middle of the cassette. I don't see how that makes sense, especially if you are bothered by the smaller gap from 15 to 17. The 52/19 at a cadence of 90 corresponds to about 32 km/h, and 52/22 to 27ish km/h, so these are not bailout gears. The 11-29 is much better, except that the 11 cog acts as a spacer, big/11 too tall for most people, and the small/11 obviousy unusable.

RussellS
Posts: 865
Joined: Wed Feb 03, 2010 1:31 am

by RussellS

basilic wrote:
Wed Dec 05, 2018 6:49 am
Before getting the 11-32 cassette, make sure you can live with the 19-22 gap, 16% smack in the middle of the cassette. I don't see how that makes sense, especially if you are bothered by the smaller gap from 15 to 17.
I hate the 11-32 cassette cogs used by SRAM and Campagnolo. 11-12-13-14-15-17-19-22-25-28-32. Or with twelve speed 11-12-13-14-15-16-17-19-22-25-28-32. The last cogs should be 17-19-21-24-28-32. Far superior progression of gears.

alcatraz
Posts: 2153
Joined: Mon Aug 29, 2016 11:19 am

by alcatraz

If you need to downshift from 19t just drop to the small chainring.

Sure 16% isn't ideal but in the big ring you shouldn't really be to far to the left anyway.

Instead of 16-17-19-22 maybe they could have done 16-18-20-22.

/a

NickJHP
Posts: 257
Joined: Wed Feb 14, 2018 2:22 am
Location: Canberra, Australia

by NickJHP

I use 44-30 chainrings and 11-28 cassette. 44-11 is exactly the same gear as 52-13, and when I started racing in the early 1970s that was the standard top gear - riders won the TdF with that as their big gear. Unless you have team managers banging on your door wanting to get your name on a Worldtour contract, you don't need anything bigger.

jeanjacques
Posts: 190
Joined: Thu Apr 14, 2016 11:01 am
Location: France

by jeanjacques

NickJHP wrote:
Wed Dec 05, 2018 10:06 am
I use 44-30 chainrings and 11-28 cassette. 44-11 is exactly the same gear as 52-13, and when I started racing in the early 1970s that was the standard top gear - riders won the TdF with that as their big gear. Unless you have team managers banging on your door wanting to get your name on a Worldtour contract, you don't need anything bigger.
Nobody want to hear that, if you don't have a 52 or 53, your are a tourist, nothing more. I'm in a cycling club (french cat. 1&2) with a 46-30 and 11-26 (Sram 11-28 sometimes), no problem at all and a perfect range of gear without any gap. At flat cruse speed around 27mph (43kmh) chainline is not that bad with still 2 or 3 cogs.
But I think, there are several things to consider for sub-compact setup, it works better with small crank (I'm 1m85 with 170mm crank) and bigger tire, 25 or 28c on modern rim give around 30mm or more so this 46-30 is not the same than with 23c tire and 175mm crank.
The cycling area is also a parameter (the most important one in fact), I live on a very hilly place with a lot of climbing at more than 15% and going downhill very fast is impossible (tight turns).

So if you want to pedal down a straight hill in a competition mode at more than 45mph (70kmh), the 46-11 wont be sufficient. Also, if you spend a lot of time in a peloton on a flat area, that the same, the sub-compact ins't the best way. But if, like the op, less front shift is the point, a 46 font give you the opportunity to act like with a 1x transmission and make few front shift.

by Weenie


wintershade
Posts: 239
Joined: Mon Apr 16, 2018 7:12 pm
Location: San Francisco, CA

by wintershade

NickJHP wrote:
Wed Dec 05, 2018 10:06 am
I use 44-30 chainrings and 11-28 cassette. 44-11 is exactly the same gear as 52-13, and when I started racing in the early 1970s that was the standard top gear - riders won the TdF with that as their big gear. Unless you have team managers banging on your door wanting to get your name on a Worldtour contract, you don't need anything bigger.
I never really understood this kind of thinking. If ancient gear was so great, why aren't you riding that same 1970s bike today? I am sure Eddy Merckx would have killed to travel forward in time and bring a Campy 12 speed groupset back to 1970. Put another way, hospitals in 1970s were good enough to keep my grandfather alive, but if you had a heart attack woudl you rather go to a hospital with 1970s or 2018 equipment? My daily driver has more horsepower than the Ferrarri I lusted over as kid, and I still want more.

Analogies aside, maybe I'm doing something wrong, but I find that being able to pedal on technical or windy descents gives an extra bit of steering input which I often appreciate. So there is also that benefit, for me, of a 52x11 vs a 50x11.

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