Double vs compact

I ride a compact with an 11-28 cassette, and it seems to work great. I do spin out sometimes going down big hills, but the low end gearing more than makes up for it.

If you are interested, I've got one of these new in the bow that I can give you a smokin' deal on.
http://www.trisports.com/fsaslkmecaco.html?productid=fsaslkmecaco&c...

I moved from a triple (52/42/30) with a 12-25 (9 speed) to a compact (50/34) with an 11-25 (10 speed) this year.  I don't think I'm quite strong enough to push a full double yet, especially since I ride up things like Lefthand Cayon to Ward and Flagstaff fairly frequently.  Going from the triple to compact here's what I found.

the triple was 3x9 = 27 gears.  2 sets were duplicates, so 25 unique gears.  But you can't really use the extremes because of chain kink... so I'd basically not use 4 of the gears like 30&12, 30&13, 52&25 and 52&23.... which effectively gave me 21 unique usable gears.

At 90rpm on 700x23s my speed range was 8.4mph to 30.5mph (obviously you can spin slower and faster than 90rpm to push the limits).

The compact gives me 20 unique usable gears though, I still tend to avoid the two extremes though since they are fairly close in gearing to other usable gears.  But at 90rpm my speed range is from 9.6mph to 32mph.  So I lost a little on the low end, but gained some on the high end.  I'll never go back to a triple for sure... If I need to drop a little lower in gearing I'll make (or find) an 11-27 and it'll bring that low gearing down to 8.6mph (which is close enough for me to a triple)

As for a full double, assuming 53/39 with an 12-27... your 90rpm translates to 10.2mph to 31.1mph... an 11 tooth rear would put it up to 33.9mph.

I know all that changes how close gears are to each other in between and stuff, but I typically don't care as much about the middle gearings since there's so many options at that point, but the extreme low and high ends matter to me.  IMO anyone that hasn't been riding for a long time and has a real good understanding of what gearing they need should go the compact route.  You lose a high gear compared to the full double, but gain on the low end.

If you can't push 32mph on the flats then you'll only notice a lose on the downhills (which by the time you're doing 35mph it's nice to give your legs a rest, get a drink, etc)  If you can't push the double going up hill you're going to be pedaling squares and killing yourself before the run.

If you haven't seen Sheldon Brown's page, you should check it out and you can compare the difference of what you have, what you are thinking about, what your friends have, etc. http://sheldonbrown.com/gears/


Edited because of bad grammer... mis-using "your" & "you're" would have bugged me.

Edited by zionvier 2009-09-24 3:24 PM

I use a triple and haven't found a hill I can't climb with it, but I am still pedaling on the downhills when my friend with the compact has run out of gears.  Sorry I don't know what the gear ratios are. 

I have some advice that a friend who was a bike mechanic and competitive track racer gave me.  More or less it was "you can't polish a turd."
So take a look at your components especially and other parts of your bike.  If you're considering a new bike, it's not really worth upgrading your current bike if you're running tiagra, etc.  When I wrecked my last bike, I had considered buying a new frame and putting my old components on it.  What I would have ended up with was a nice frame with low grade components (which do all the work on a bike). 
What I'm saying is that if you're thinking of buying a new bike and your current bike isn't that great, it's probably just worth it in the long run to get the new bike with better components and the crankset you want.  If you're not sure and you're just breaking into triathlon, spend a season on what you have and see if you like it (you will).  If you've got a good bike now with good components, then it's probaby worth upgrading the crankset and throwing aerobars on.

I've heard great things about compacts and they take the hassle out of the triple.

If you're looking to set up your bike primarily for the tris you'll be doing, and the the tri-specific training you'll want to do to get ready for those tris, I don't think you'll want to go the route of the compact. If you want to use your bike for doing a lot of climbing as well, though, then a compact make make some sense. If you do go the compact route, you'll want to make sure you get an 11 on the back. You'll definitely use it on the flats on downhills in your tris.

Thank you for all the advice.  I think I'll hold off on upgrading components and put that money towards a tri bike in a couple of years. 

If you're relatively new to cycling or just starting to really ramp up in cycling, don't worry about the equipment. Instead, invest your time/energy in doing what you need to do regardless of equipment: ride. Your current equipment will likely be more than adequate for most ride terrains and training plans. Triple/Double cranks, standard/compact rings, 11/12 cassettes...all personal and really don't make a substantial difference in the end results. Unless you're a cat 1 roadie, chances are you won't be spinning out anything unless you're going downhill, and even then, the difference between 35 mph top end and 38 mph top end is not going to catapult you from BOP to FOP racer. Ride your butt off w/ what you have; as your experiences in the saddle grow, so will you understanding as to what will likely work best for you.