ok, gotta admit some ignorance on my bike parts - I’m looking at buying a new bike, and my LBS (the guy’s fantastic) recommended a compact crank. I’ll go with it, but I’m just wondering exactly what it is, why I need it (BTW, I’m at 5ft 2in 120lb female looking at a bike with 650s), what it gets me, etc.
Hmmm…what kind of terrain are you mostly riding on? Hills or flats? I love my compacts on my tri bike with 700 wheels. I had a 55\44 on my tri bike with 650 wheels, although in retrospect 53\39 would have been fine.
There are many, many fine threads on this forum discussing the ins and outs of compact cranks. I’d hate to generalize, but basically compact cranks allow an extra ‘low’ gear to spin in. Most riders don’t need the high end gear, and especially in a tri it is usually beneficial to be able to keep a constant cadence without standing or mashing. Compacts lend themselves to that very well.
But on 650 wheels it may be overkill, unless you are in a hilly area I guess.
If you ride down hills or in a tailwind, or if you time trial or are a strong cyclist, get traditional chanrings.
Compact rings have their place, usually for smaller riders.
Compacts basically serve a similar purpose as 650’s, only in a slightly more convenient package. I’d say both would be overkill. My gf is similar size to you, and rides 650’s, and she does fine with a 53/39 (normal) front with a 12/25 cassette in the back, and we live in very hilly territory.
Very true Gary, but wouldn’t she typically have to ride UP the hills before riding DOWN them?
I do very much agree that if she is doing TT or if she is (or soon will be!) a strong cyclist she would be better off on traditional chainrings, especially with 650 wheels.
I’m riding alot of hills - pretty steep ones too, I’m in the Bay Area.
So my big take-away is that a compact crank may be overkill with 650s, but not a problem. Anything else?
go with a 39/54 or 42/54
or 39/53
skip compact
FWIW, I have spun out a 54x12 at 90-100’ish rpm for 25 minutes on the flats, 15mph tailwind, 700c.
Yup. A compact paired with an 11-23 gives you a better range than 53/39 paired with 12/25 in terms of biggest/smallest pairing.
Oh, I also forgot. You really should get a compact-specific front derailleur. The jump from 34->50 is 16 teeth. Most FD’s are meant for 14 teeth (53-39). So if you use a regular FD with a compact, your shifting up front won’t be as smooth.
I’d really avoid it, if only for the above reason. You definitely don’t need it…
a 12/27 cassette will be your best bet. That’ll do you just fine. Plus no worries about a special FD…
Yeah but are you a 5’2, 120 lb female? 
The very first few months I started cycling and training for tris I would spin out of 53x11 with 650 wheels every time I hit this one certain flat section of my training ride. For that one section only I was hitting 28 mph easily, sometimes flirting with 30+! I thought it was my legs, so naturally I went to the LBS beaming to get my 55. After riding much more, I realized that my ‘fast’ section actually had a VERY slight downgrade and that there was ususally a tailwind. So much for skill, right?
I have 50/34 compacts on my road bike and would never go back to regular cranks. They are explained quite well here:
It appears no one has answered the most elementary question, so here goes.
A compact crank isn’t exactly compact, its just a name. The cranks arms are the same length. The “compact” portion is the spider in which the chainrings are mounted. This allows you to put a smaller-than-traditional sized chainring on the front. However…the BEST (IMO) part of “compact cranks” is that you can always put traditional (53/39) cogs on the front, although they are getting hard to find now.
Many folks who buy compact cranks are also folks that would ride a triple chainring in front, but do not want all the weight and hassle.
It’s tough to know in your case w/o more information. Trust your LBS. My 2 cents at your height is to double check to make sure you are getting the proper LENGTH crank as many LBS may put standard length cranks on a bike for smaller riders…
Good luck!
A few people have tried to answer this, so I’ll take a shot using some different language.
Compact cranks make it easier for you to climb hills, and they make it easier for you to find a gear combination that feels right for the terrain.
Easier to climb hills: Especially in the first 6-18 months of cycling, when you’re falling in love with the sport but still developing the strength and technique for it, it’s very common to overreach and ride further than your ability – you go down one too many hills that you have to come back up. With compact cranks, the small ring in the front is much smaller than it is on traditional cranks. That means that you can make it very easy to go up hills at a reasonable cadence, instead of grinding it up the hills on already fried legs. If you live in the Bay area, it probably means the difference between having to stand on many climbs and being able to sit and spin.
Find a gear combination that feels right: Because the front rings are smaller, the back gears can also be smaller. That means the gears in back can be closer to the same size, allowing you to fine tune your gearing. I can’t think of a way to explain this without numbers, but it’s pretty straightforward. If you have traditional cranks with 42 teeth on the small ring, you may need 25 teeth on your largest gear in back in order to get up the hills. 42/25 is a ratio of 1.68. To achieve the same ratio in compact cranks, with 36 or 34 teeth on the small ring, only requires 21 teeth in the back. If you look at the available cassettes that have 25 teeth, they skip some sizes in the smaller gears – there’s no gear with 18 teeth or 20 teeth, for example. If you look at the cassettes that have 21 teeth as the largest gear, they do offer gears with 18 teeth and 20 teeth. In fact, the 12-21 ten-speed cassette has gears with 12, 13, 14, 15, 16, 17, 18, 19, 20, and 21 teeth. That gives you much more opportunity to fine tune your ratios than cassettes that force you to skip a gear.
Since the bike you’re looking at has 650 wheels, it’ll already be easier for you to get up the hills (the same force will turn a smaller wheel more easily). But unless you’re already a strong cyclist and strong climber, (or you really feel it necessary to pedal down the hills faster than 30 miles an hour) you’ll probably be better served with compact cranks and a 12-21 or 11-21 cassette. Try to get the 10-speed ultegra setup if possible, and if your LBS is good they’ll be able to tell you if you need the long-cage rear derailleur or not. If you find you can’t get up the hills, it’s trivial to switch to a 12-23 or 12-25 cassette.
Lee Silverman
JackRabbit Sports
Park Slope, Brooklyn
I don’t have any experience with how 650s affect things. But to share my experience-I got a new bike about 6 months ago. My shop suggest the compact cranks but I did not like the idea for usual reasons-poor shifting, not having a high enough gear, dura ace 10 speed looks cooler, and of course I did not want to be call a p---- by my buddies. Couple of months ago, I wanted to do a very tough mountain ride. Although 6’3"/180 I am not strong enough to push my gearing up a mountain. Anyway-I bought a compact (34/50) for that ride. It is still on my bike and will stay there. After the ride, I put an 11/25 on the back and I have a huge range without all of the rear cog switching. Admittedly the shifting is not as smooth, but I think it is worth the benefits.
coming from another smallish rider (5’6", a little under 140 lb), here’s my experience. I have a 53/39 crank on my bike–on long rides and in races, the only times I use my 53t ring is:
- going down hills. even then, I don’t usually pedal above ~28 mph.
- no other time.
other uses for the big chainring: standing climbing and big gear work on the trainer, sprint races, chasing the local fast ride group after I get dropped.
advantages of the compact as I see it:
- you can spin more of the time, especially up more hills. this doesn’t mean that you shouldn’t do some training in a big gear at a lower cadence. it’s good for developing leg strength that you will need to pedal a bigger gear on the flats at race effort.
- smoother shifting. especially if you get a 50/36 instead of the typical 50/34.
- those really damn steep hills become a little less intimidating.
caveats (IMO):
- if you use a trainer much (especially if you live in a colder area) I think the workouts would get a little boring with compact gearing.
- if you do shorter road races (especially crits/track) then a compact might not be a good way to go. on the other hand, I know a couple of very fast road racers who ride compacts quite successfully.
- I have 700c wheels. I don’t know if a compact would be excessively undergeared for 650c wheels. **I would definitely ask you LBS guy about this–he sounds like a knowledgeable chap. **
the link that cerveloguy posted to Dan’s explanation of compacts is a great article.
Gary,
I think you are repeatedly proving why compact cranks ARE appropriate for most triathletes!
The logic is this IF a 53/54 x 12 is the correct setup for YOU and we take into account:
-
You are a stronger cyclist than most triathletes
-
You don’t run after you ride
-
Time trials are almost always shorter than a 1/2IM and IM bike legs that many triathletes race
-
I can’t think of any triathlon race courses in North America with 25 minutes of flat except perhaps Florida.
Add 1 + 2 + 3 + 4 and what you arrive at is IF you have the correct setup on your bike then nearly all triathletes SHOULD be riding compact cranks because they are not as strong, have to ride easier to run afterwards, often do longer races (bike portion) and don’t ride flat courses exclusively.
Now, whether someone with 650 wheels should ride compacts in a different kettle of fish. Certainly, a not very strong cyclist might still be right for compacts. A strong cyclist, probably not.
I live in the east bay. I am ok on the bike, and just took my P2SL up tunnel road in Oakland. I rode in the aero bars and stayed in the 34/25 most of the way up. But, climbing isnt my thing (6’3 210#). It would have been miserable with a standard crank and I would not have stayed in the aero bars.
Compact cranks are the way to go unless you live in a perfectly flat area or produce gobs of power.
Allen Lim (Landis’ physiologist) just commented on this a couple days ago in his daily column on bicycling.com -
“In general, I find that most riders are simply over geared for the hills. The reality is, most bikes sold today are geared for professional cyclists not your average Joe or competitive amateur. After all, the fact that a pro’s bike here in the Tour has the same gearing as that sold in your local bike shop should raise some questions. I mean, ego aside, you wouldn’t use the same transmission on an engine that is only half as powerful. So for most cyclists, instead of the standard tooth crank combination of 53 x 39, I recommend a “compact crank” combination of 50 x 34. For the everyday cyclist, it just works better because it helps keep you in that normal cadence range on steep climbs. But if you’re not ready to let go of those big chain rings, then it might interest you to know that in tomorrow’s stage - the hilliest of all the Tour stages - Floyd and his teammates will be going “compact.” In the end, it’s not about pride it’s about speed.”
The rest of the article is here - http://www.bicycling.com/tourdefrance/experts/columns/0,5976,s1-12704-527,00.html?category_id=527
Anyone racing 1/2 IMs or full IMs really shouldn’t be pedaling at speeds where you’d spin out on a compact crank anyways…the added value of the small % increase in speed does not warrant the energy/power expenditure.
FWIW I don’t have compact cranks but I would get them if buying today.
ot
Probably a strength thing,
I use a 55/11 now
Most of the guys I race with use 55,56, or 58’s
One of them uses a 63T, 700c
.
And is your mate with the 63T, 700c a 5’2, 120 lb female?
I have no point mind you, I just like repeating those measurements. Meow baby:)
umm … no, he is a little bigger
