Compact Cranks
 

Hello,

Long time old biker riding an old bike. All is well at the moment. But, I still dream of buying a new bike someday. Thing is, I just don't get this compact crank thing. I mean a crank with 34/50 teeth just doesn't appeal to me. But, alot of bikes I've looked at have them. I would prefer the 39/53 crank.

My question is, if I bought a bike with a 34/50 crank, could I just change out the chain rings to 39/53, or would I have to replace the entire crank?

Thanks for your help,

Bob

your inner bolt chain diameter is 110cm. Any 110cm chainring will do (52/36, 52/38, 50/36, etc, etc)

You can get 110mm BCD chainrings in 33t to 54t.

agreed, i purchased recently and i unfortunately got stuck with a compact and now i'm wishing i asked to swap that out at time of purchase. From what i understand, you can swap out for standard gears with relative ease. Although, you will have to move your front derailleur up a bit to fit the larger chainring, and make sure your chain length is correct (possibly new chain)... i think that's it...

oh and also, the 52-54T on a 110 BCD may not be as stiff as a 52-54T on a 130BCD, but given that pros were riding these in the hard stages of the Giro, i think you should be fine

They are basically replacing triples.

Many companies will have a standard crank option, or a quality lbs should swap cranks for little to no cash.

Gear inches.

How do they work?

- Z

Compacts give you a wider range than a normal double, so they are good in hilly areas. .... maybe you'd like it ?

From the master, Sheldon Brown http://www.sheldonbrown.com/gain.html

Gear Inches
The simplest system in common use is the "gear inch" system. This dates back to before the invention of the chain-drive bicycle. It originally was the diameter of the drive wheel of a high-wheel bicycle. When chain-drive "safety" bikes came in, the same system was used, multiplying the drive wheel diameter by the sprocket ratio. It is very easy to calculate: the diameter of the drive wheel, times the size of the front sprocket divided by the size of the rear sprocket. This gives a convenient two- or three-digit number. The examples listed above are all around 74-75 inches. The lowest gear on most mountain bikes is around 22-26 inches. The highest gear on road racing bikes is usually around 108-110 inches. Unfortunately, the handwriting is on the wall for all inch-based measurement systems.

Why wring your hands over it? 50/11 is a bigger gear than 53/12, so it's not like you will loose any top end speed with the proper cassette. Aside from shorter chainlife, there is no real downside to a 50/34 with a 11-23 or 11-25 cassette, unless for some strange reason you spend alot of time at 35+mph.

Exactly what I was thinking.

I have to agree I ride one bike with a 53-12 and the other is a 50-11 and basically I have the same gear range a little more on the compact. I suppose if I go to an 11-25 on the standard double I am ahead but really how often would I actually use it? Maybe in a huge tailwind, we don't have downhill mountains in the flats here. I think the 50-11 does the trick with an my 11-23 on the rear, I like this set up I never go to the small ring much at all. I have done 50 mile rides and never came close to going to the small ring. The great thing is that it is there if need in place where I am wipe out. I finally got over the issue but I still like a standard double but at almost 50 I have to think it is ok.

Most bikes I have seen sold in bike shops are available in either a standard or compact crank. If you don't live in an area with lots of nasty hills then by all means, get a standard. However, a compact does give you a wider range of gears than a standard. A 53X12 on a standard is a smaller gear ratio or slower gears than a 50X11 on a compact.

I just find that on my compact, I have too much of an in-between. When I'm riding in the flats, my 34-12 (small-Small) I find myself needing a higher gear but then going to the big chainring, I have to switch the front too much.
I've thought about switching the little ring out for a 36 or 38.

I think for most mere mortals a compact crank makes more sense. I went from a 54 big chainring to a 50, and I don't think there are any places I have spun that gear out yet.

Whether I spend "a lot of time" at those speeds or not, when I want my 53x11, I generally want it bad. For example, downwind sprints at Spokane County Raceway can get into the 40mph+ range, and I'm not one of those gifted 120rpm-out-of-the-saddle guys. It would be silly to go to that course with an inadequate high gear on the grounds that "well, I'll only need the 53x11 for the last 200 meters, so why bother having a 53x11?" ;)

bhaubold, another factor to evaluate is the jump between the rings. The jump from a 34 to a 50 is about a 15% larger drop in RPM than the jump from a 39 to a 53. In practical terms, it means there's usually one more rear shift required to compensate for a front shift, and less overlap in the speed range of the two chainrings. That can be viewed as good or bad, depending how you ride and what you like better.

I do have one of each myself... the rain/commuting bike currently has compact. When I change it from 9sp to 10sp, it's going back to full-size, though... personal preference, I guess.

Oh, and to address the actual question: rather than changing rings on the compact, I'd recommend getting a non-compact crank if you want full-sized chainrings, for flex reasons.

I went from a compact to a standard and am looking to go back. I had a 34/50 with an 11/23. Top speed was faster than it is on 53/12 (I usually ride a 12/25 now for better all around gearing) I put the 11/23 on my race wheelset but never hit the 11. I want that semi granny gear back!

My .02 is compacts are great for recreational riders like me. Cavaet is as mech stated well...big jump from 50 to 34 which I never like for shifting or pedaling. For that reason I ride 50/38 which is perfect for the relatively rolly but flatish land I ride. A concept that gets lost on many is...gear redundancy is good and not bad. If you don't need the gear inches on the top or bottom then overlap between rings is a very good thing because either ring serves the purpose more fully and shifting between the rings is more seamless with less rear shifting to equal gear inches. If you aren't a brute and don't need to scale Everest...a 50/38 is a fabulous compact combo. Even with compact Campy you can get a generic inner ring to fit with a bit of dremmel surgery to the single offset mounting hole.

50/34 with 11-23 rules (what I run)

I've got 50/34 and 52/36 rings for my cranks (Red and S975 PM). That gets me close to 53/39 but not quite. If I ever get to where I can spin out the 52/36 for a prolonged period I'll consider moving up. I don't really see that happening so I'll spend the money on spares instead. GL

I use 50/34 with 12-25 (9 speed) and I don't seem to run out of gears on the high end though there are no real hills around here. Since I'm always riding solo and usually commuting, the lower gearing seems to be more appropriate for me.

From the rare times I have gone on rides maintaining a 22-24 mph pace, I could see where the 53/39 would be better however for 99% of my riding the 50/34 is fine. Sometimes when it's windy and cold/rainy with my backpack on, images of Apex dance in my head :)

I like a 39 chain ring for my local riding. I don't often need the 53, and never need anything smaller. I spend most of my time in the 16 to 24 mph range, and it serves me well. When I ride where there are steep inclines, I use a triple, but a compact works there too. If you are fortunate to have terrain where one ring suits your abilities for 90+ % of your riding, get that ring and enjoy ignoring the front dérailleur. I think most people who are dissatisfied with a compact crank are annoyed at the need to shift the front often in their usual riding.

I love my compact and I live in northern Indiana.

It does seem a little difficult to find the right gear when riding in the flats. I often find myself jumping back and forth on the front rings, searching for the perfect gear.

Using a relatively wide range cassete helps with that. Like someone else said above, you want some overlap in the gearing ranges of the two chainrings.
If I could get up all the climbs I want to climb on a 34x23 I'd use a 36 small ring and a 1x-25 cassette. That way I could use the 23t next to largest cog with the big ring so I can stay in the big ring longer. As it is I run a 50/34 and 12-27... there's some long steep climbs here.

Gotta say I appreciate this thread! Currently running 50/34 and 11/21 (10s), but am getting killed on the hills, however I do hit the 11 on occasion in some areas and never the 34. I'm thinking of going to a 23 on the back to stay off the 34, but don't have the knowledge or experience to know better either way, but from what I'm reading that seems to be the way to go.

Just how bad is it to be totally topped out, meaning 54/23? Is it a wear issue or potential mechanical failure? I'm pretty strong legged and haven't snapped anything, yet!

Glad I found you all!! :)