For what it is worth, a 39/53 crankset is the standard option. Compact crankset (34/50) are in general for hilly course. Semi-compact (36/52) are for all-around course. I would say if you are a strong cyclist, go for the 39/53 (or 54 for flat TT). If you feel there's work that could be done on your cycling, go with the 36/52 or the compact as it will force you to have a greater cadence instead of destroying your legs on the 53 (or 54) ring.

172.5 crank arm are the standard option. 170mm (or less) will up your cadence (95+) as the circle described by your foot will be smaller than 172.5 or 175mm for a given rpm. 175mm (or more) are for the guys that like to hammer on the bike without having a high cadence (85-).

Medium cage derailleurs are for cassette that have their larger cog up to 28 teeth. Long cage derailleurs are for anything more than 28 teeth.

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-D

very helpful, thank you!

David, just curious...when do you usually replace the chainrings? I assume it's not nearly as frequent as the cassette. Or is it even necessary (outside of damaged teeth, slipping chain, etc.)? Thanks.

Oval. All the evidence points to the fact it's faster.

*runs for the door*

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The curious task of economics is to demonstrate to men how little they really know about what they imagine they can design.

Chainrings are changed very rarely (as long as you take care of your bike).
You got it. It's time to change the chainrings when those things happen but also when the teeth become to be "sharp edged". So it's very rare to change chainrings only because they are worn out. You may change a lot more chains and cassettes before changing chainrings.

Thing to not forget:

1. Change your chain every 3000km or so. This way, the life of your cassette will be way longer.

2. When your chain is skipping some gears on the cassette while riding and pushing hard on the pedals, assuming your followed rule #1, your cassette needs to be changed.

3. Don't ride a worn out cassette. It may be a disaster in group ride.

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-D

Can you point me to any of this?

I use to run a 53/39 on my old bike but found I very rarely using the small cog on the 12-25 cassette, essentially I was using a 9 speed. I live on coastal FL and suffered up some central FL & out of state hills with it a few times. I changed the cassette to a 13-25 junior cassette, gained the 18 cog, and only ran out of top gear once on a sustained effort when I had a 30mph tail wind. Bottom end still sucked though. My new bike has a compact 50/34 and all Ultegra 6800 with short age. I'm running a 12-25 11-spd cassette. Its a bit faster on the top end at the same cadence(0.5-0.7mph at 70-100rpms) with the taller 50/12 (rear wheel spins 4.167x per one crank revolution) vs 53/13 (4.077x) but now I can climb much better. I signed up for several hilly races last year an had no climbing issues with the 34 chainring.

IMHO, a majority of triathletes/riders can use a 50/34 everyday and adjust the cassette to match the needs. Supposedly a Midcage is needed to run bigger cogs like a 32+. I've read Shimano is conservative with their specs and others have run the 32 with the short cage.

What's nice about the latest Shimano Hollowtech II cranks is the fact that the chainrings can now be whatever size you want; 53-39T / 52-36T / 50-34T / 46-36T.

I use to run a 175mm crank arm, wanted to go to 170-165 to open up my hips more but could only get 172.5 when I ordered the crank. I can't tell the diff as the new bike fits me better than my old bike did. (5'10 long torso).

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<We all know that light travels faster than sound. That's why certain people appear bright until you hear them speak>

 
I just went through this same process, always rode whatever came on the bike, finally had to do something different in the past couple of weeks. My TT bike came with a compact 50/34 and a 12-25 in the back. My roadie had a standard 53/39 and a 12-25 in the back. Both cranks are 175mm long, and both setups are 10 speed.

I am heading to CA in two weeks for a week long training camp, will ride 500 miles over the course of the week and have some 10k+ climbing days. I did not want to do some of the steep climbs with my standard so I started looking at options for new front crank. I found that I could run a 50/34 up front and change to an 11-28 in the rear and gain a ton of usable gears for steep climbs. So I thought, that's great for climbs but what about hammering back down the hill, I'm gonna run out of gear too fast. I found out that the 50 up front and the 11 in the rear is actually a taller gear than the 53 in front and 12 in rear I was currently running. So I swapped to 50/34 and 11-28, gained a ton of room for climbing and even increased my top speed spin out. Win win IMO.

I found that the vast majority of my riding group is running compact, it is very versatile and the only real limitation would be long descents where you want to do more than 40mph. I am generally tucked worrying about handling at those speeds so I am not too worried about it.

If you know nothing the other things you may want to know is there are 2 bolt patterns 110BCD and 130BCD. Why is this important? Well you can obviously have different chain rings to swap onto a single spider. Effectively you could have 54,53,52,50 big rings and swap them out depending on course like the cassette(which is the more popular way to do this). While this isn't popular if you start getting into Rotor Q Rings or want forged rather than milled rings you'll want to know the bolt pattern on your spider.

So think of it as 4 parts on a double setup:
1. Crank Arms (L+R)
2. Small Ring
3. Big Ring
4. Spider

Most of the newer stuff is all 110BCD and the older 130BCD for road bikes. There are a bunch of other bolt patterns for MTB, Track etc so it's good to know which you have and which works with your type of bike.

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"Train so you have no regrets @ the finish line"

We can't really recommend chainrings/cassettes to you without knowing a lot of information. Where do you ride? What's your FTP? What's your CdA? The easier way is to take a look at the gearing that you have. What do you like about it and what do you want to change? Do you want a higher top end? Or a lower low end? Smaller jumps between shifts?

My best advice would be to figure out what gearing you have and play around with this gear calculator to figure out what kind of gearing you would like.

This conversation is so interesting. I know mountain bike drive train exceptionally well. In that sport you change rings annually, except for after the Iceman race, then you changed EVERYTHING.

Good education here on the road side of things.

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The curious task of economics is to demonstrate to men how little they really know about what they imagine they can design.

Good advice from durk onion...it really is hard to say. Gearing is so personal.

Play around with that gear caluclator, and take a look at the speeds you generally hit when riding, and your preferred cadence. Think about the terrain you ride as well. I'll probably get flamed for this from the HTFU police, but at 100rpm a 50x11 (50t cog front, 11t cog rear) will give you over 35mph. At 90rpm, it is still 32mph. I believe that 90% of the time, a 50/34 crankset and 11-25 cassette will cover you. 11-28 is nice to have if you hit hills regularly. 11 speed makes 11-28 an even nicer choice, because you get the nice tight gear cluster of an 11-25 plus an extra climbing gear.

52-36 is a nice option if you do a lot of group riding or regularly hit speeds over 35mph. 52t is a bit too much for me...that's me personally though. I'll run an 11-23 for racing, and an 11-25 or 11-28 for training. The 11t does the job for the odd big downhill I hit (compared to a 12t), I would recommend that before going bigger on the front. Again though, personal preference. Welcome to the wide world of gear configurations :)

Another factor that has not been brought up is wheel size (and to a much smaller extent tire size). If you are on 650c wheels, a 50X11 is a very small gear.

Generally most people are on 700c wheels, but it is something to keep in mind if you are recommending gearing.

I second this, there is plenty of fan boys in my area that tried to bring me down and my compact crank.
Until they actually cried when I can smoke them up hill and then some!

My favorite Combo is 50/34 with 11-26 cassette(SRAM).

Fair enough! An unfair assumption I made.

OP are we talking 650c or 700c wheels? If 650c, then I'll have to retract my advice...