Compact Crankset vs. Full Size

See the charts below. The Compact Crank gives you more top end speed and more range on the bottom end.

This is assuming that you have the choice between a compact and regular crank. If you already have a standard double, then a cassette change can probably do what a compact will do.

As Bicycling Magazine said, the compact crank will soon replace the triple crank on most bikes.


Gear chart using MPH @ 100 RPM
For 700 X 23 / 23-622 tire with 172.5 mm cranks
With 9-speed 12-13-14-15-16-17-18-19-21 Cassette
53 39
12 34.5 25.4
13 31.9 23.5
14 29.6 21.8
15 27.6 20.3
16 25.9 19.1
17 24.4 17.9
18 23.0 16.9
19 21.8 16.0
21 19.7 14.5


Gear chart using MPH @ 100 RPM
For 700 X 23 / 23-622 tire with 172.5 mm cranks
With 9-speed 11-12-13-14-15-17-19-21-23 Cassette
50 33
11 35.5 23.5
12 32.6 21.5
13 30.1 19.8
14 27.9 18.4
15 26.1 17.2
17 23.0 15.2
19 20.6 13.6
21 18.6 12.3
23 17.0 11.2

Honestly, I think that a compact crank with 12/23 or 12/25 is the appropriate combination for most triathletes regardless of hills or not.  Folks on SlowTwitch will flame me for saying that because surely you need an 11 on the cassette and a big TT ring up front if you're a real cyclist.  In reality, I doubt anyone will spin out a 50/12 unless they are screaming downhill and they're probably better off using that time to rest their legs anyway.  I prefer to spin up the hills so the 39/25 is a good choice and I'd even go to a 27 for very hilly courses.  I like to keep my cadence around 95rpm and climbing hills last week on my century ride I was in the 39/25 pushing 80-85rpm.

Compact with a 11/23 rear cassette gives you the same climbing ability of a 27 and more top end speed. Dumb to use only a 12...negates half the advantages of a compact crank. Most would be hard pressed to need more climbing and most will use the 11 at some point on a typical tri course.

36/27 is a mtn bike gear set. 36/25 is getting there. Typically 39/27 si the biggest gear set you'll see on a tri bike at places like Lake Placid and a 36/23 duplicates that.

I have compacts on 3 out of 4 of my bikes includsing my tri bike. But I also run a 11/23 on all but one of them. The exception is a bike built specifically for climbing and has a 12/27. I use it on things like long 20% to 33% grades locally. If you are under 200# a 11/23 will get you up pretty much anything you can pedal.

Edited by Nob 2006-08-13 1:27 AM

If you are running Shimano you don't have a tigher ratio with a 12/25 compared to a 11/23 just the opposite in fact. 12/21 is tighter than a 11/21, which is tigher than the 11/23. 11/23 tighter than the 12/25. 12/25 is a tigher gear ration than a 12/27.

11-12-13-14-15-16-17-19-21-23T Three 2 tooth gaps
12-13-14-15-16-17-19-21-23-25T Four 2 tooth gaps and a lack of top end at 90rpm made worse yet if you are trying to spin out your legs to freshen them past 90 rpm. Your gears with a 12/25 are now similar to a 27t sprocket and a 30t sprocket in back on a 53/39. That is some serious gearing for climbing or spinning.

Having done it more than once I don't see the rational to use a compact and a 11/23 on a completely flat course. You still have the same gearing as a 53/39 with a 27 so you are wasting 2 gears minimum, 21/23. 11/21 or a 12/21 do make some sense on a flat course or better yet a bigger front chain ring.

Here are the other gear rations on a 10 speed Shimano set up.
12-13-14-15-16-17-18-19-20-21T no gaps
11-12-13-14-15-16-17-18-19-21T One 2 tooth gap.
12-13-14-15-16-17-19-21-24-27T Four 2 tooth again but with a added 3 tooth gap now.

Unless of course you really want to spin in 23T at 90rpm and 10 mph.
At least a 21 will make 11.5 mph at 90rpm.

I've been using compacts for some time now. Don't plan on changing that. But the biggest advantages to a compact are tigher gears if you use the right cassette, a easier set of climbing/spinning gears and a ligher weight drive chain set.

Obviously you need to choose the gears that work best for you. To do that you need the correct info to judge against your riding style and local terrain.

One of the best ways to see what cassette really works for you is on long rides. Do you ride a straight chain? If you are running a tightly crossed chain say the 36 in a 11/12/13 or the 50 in a 21/23/25 you are not riding the right casette for that ride.