pharding

What are the benefits of a compact crank? What type of rider should look at a compact crank?

botto 

lighter gears for climbing.

depends.

next question.

climbhoser

Next question: when is Botto going to sprout his beginner nub?

As for compact cranks, the idea is to give you more of a low range than your typical double, by sacrificing some of the middle range.

Your big ring gives you the high range, which is probably where you'll spend most of your time on flats or slightly rolling terrain. The little ring gives you a low range for billy-goating mountain passes and such.

Here in CO we see lots of 'em for exactly that reason, because we can get by with the big ring in the valleys and use the wee one for the passes. Some people use them for touring to replace Triples if they like life more simple.

I have a 50-36 compact double and a 12-32 cassette in back because I don't really need the minute gear jumps for hanging with a group (I rarely ride with a group, and if I do it's my buds from college not a hardcore outfit), but I do quite a bit of billygoating.

Retro Grouch 

The benefits are easy. A 34 tooth chainring is smaller than a 39 so you'll have an easier hill climb gear.

The drawback takes some explaining. It's lack of overlap. If you're used to nice, tightly spaced gear changes, when you shift chainrings on a compact you'll find yourself having to make a couple of gear changes on the back to access the next gear in sequence. If you only find yourself doing that at the start of a big hill, like the poster from Colorado suggested, it's not a problem. If you find yourself changing chainrings a lot on a flat road or if you ride a lot of rolling hills, a compact crankset can be a PITA.

Fird

ok, excuse my n00bishness but just to confirm that the only thing that changes in a 'compact' crankset is the small chainring?

KevinF

No. Standard doubles have 53 and 39 tooth rings up front (usually). Compacts have 50 and 34 (or 36) tooth rings up front -- i.e., both chainrings are somewhat smaller. You sacrifice a bit on the high-end, but you get it back on the low end.

urbanknight

More specifically, it allows you to put a smaller chainring on it than a standard. You usually use a smaller big ring with that as well. For example, compact cranks commonly come with 50/36 or 50/34 while most standard ones (today) come with 53/39.

AEO

"regular" cranks have a 130mm or 135mm BCD (Bolt Circle Diameter)
"compact" cranks have a 110mm BCD

you can't swap rings from regular to compact and vice versa.

maddyfish

No. Usually a standard is 53-39, or older 52-42. Compacts are usually 50-34 or 50-36

billallbritten

One thing that helps is the feature on Veloce > Record Campy shifters pre '07, Chorus > Record 07,08, back to Veloce > Record for 09, of multiple shifts in both directions on the cog with one shift motion.

That is, if you shift to the small chainring, you can shift higher (to smaller cogs) in the rear by 2 or more steps with one thumb press of the thumb lever.

Similarly, if you shift to the large chainring, you can shift lower (to larger cogs) in the rear two or more steps with one swing of the lever.

My understanding for '09 is that all Campy shifters, Veloce > Record levels, will shift the cassette up to 5 higher (larger to smaller cogs) with one thumb press and shift up to 3 cogs lower (smaller to larger cogs) with one lever swing. Robbie McEwen rode on Monday, a bike equipped with 2009 Centaur shifters with an older 2x10 gearset. REF:https://velonews.com/article/79345

I like to pedal at a reasonably high cadence, 105+, on level ground, so, in our local group, we typically cruise at 20-22 mph, and pick it up to 24-26+ for short periods, I stay on the 34/13,14 combinations and spin. Climbing is easy as I'm already on the small chainwheel, just downshift to larger cogs by whatever steps are necessary.

Faster riding, I shift to the 50 chainring, and go 2, 3 or more steps lower (to larger cogs) in the rear. If I'm going fast and hit a hill, upshift to 34 in front and go to a much lower (larger cog) gear in back. My older ergo shifters will sweep the cassette in two shift lever/paddle motions in either direction. New ones will require 4 to go from 12>25 or whatever on 10,11 speed, 2 to dump 10 cogs going down in back

Much more complicated to write out than do.

This was one reason I went with a Campy equipped compact ride in 06, the ability to sweep up and down the cassette.

Note, the 50/34 combo is really not that much larger a drop than 53/39 so it's a bit of a tempest in a teapot IMHO to worry about the 16 tooth drop in front.

Fird

Thanks for the compact crank explanation!