TheRCF

I'm thinking about changing my double crank (39/53 right now) because I need lower gears for some pretty big hills I'm working on. I have a 12/27 cassette.

One is to go all the way down to a 34/50. If I did the calculations right, this would make my lowest gear almost excactly the same as if I had a 31 on the rear. But a mechanic told me some people are not happy about the shifting with a 34/50 and maybe I should just do a 36/50 which he said no one seemed to complain about.

A 36 would be just a bit better than having a 29 cog in the rear.

Later I started wondering if a another possibility was a 35/50 (like having a 30 cog in back).

So, I need feedback on people's experience with the 34/50 mainly, plus any comments you may have about the other two possibilities.

Thanks.

roadfix

I've never seen a 35 ring.
As long as the FD is set and adjusted correctly, 34/50 shifts perfectly fine...

TheRCF

Two questions about that:

1. While shifting "perfectly fine", is there a different feel to it (something may work "fine", but have characteristics that may bother some people)?

2. Is the adjustment more sensitive - that is, less of a range of position where everything still works?

roadfix

Using the exact same Campy derailleur, I don't see or feel a noticable difference in shifting performance between my new 50/34 and my old 52/39 cranksets. Perhaps Campies are less finicky & sensitive than Shimanos in these areas.

SteveE

You may need to shift to a smaller cog concurrent with shifting to the smaller chain ring. This is to avoid too big a jump when going from the 50-tooth to the 34-tooth chainring.

TheRCF

That is a factor? The mechanic didn't refer to that being a possible problem - just the 50/34 factor itself because it is about at the limit of what the derailer can handle. Even then, he said his comments were based on just some comments from a few users who may not be representative.

Based on the Felt bikes in the shop this year, it looks like 34/50 is becoming their standard. It does seem strange that they would do that on so many bikes if there were problems, but still, it may be. That's why I hope to find a number of posters with experience with them.

SteveE

TheRCF -

Your original post didn't mention derailleur limitation, just that some people were not "happy" with the shifting. I jumped to the conclusion that the reason they were unhappy was because of the difference in gear inches when shifting from the 50 to the 34 tooth chainring.

FWIW, I recently switched from a 30/42/52 triple to 34/50 compact double. I do find that I like to do a double shift when going from the big chainring to the small one in order to avoid spinning like crazy.

TheRCF

I don't know much about mechanical things, but I've had people tell me that a gap of 16 teeth is the limit. No one has told me otherwise so I assume they are correct.

I don't know the details of why some people are unhappy with the shifting - just that some weren't (hence my asking about possible problems here).

I see what you mean now about shifting the rear - I do that with my present setup. In my case, I'm going down a pretty good hill (just short) and will be in my higest gear. This is immediately followed by a short but steep uphill (steepest at the end). As I start climbing, I keep downshifting, but at some point, I need to drop to the small ring. Usually I stand for a short time to maximize speed which means I can use a higher rear cog than when sitting. When the speed really starts to drop, I drop to the small ring right after I sit down and it will be about where it needs to be.

Retro Grouch 

I doubt it. I've got Ultegra shifters and derailleurs and my experience (on only one bike) is the same as yours.

I can see a problem that many riders might not like. When you shift from the big to the little chainring, you need to shift up one or two gears on the back. If you find yourself doing that very often on flattish ground, that would be a major PITA. If your chainrings and cassette are matched so that most of your flat road riding is on the big ring and the middle of the cassette, it's not so bad. In that case you probably are only shifting into the little ring as you start up steeper hills.

bmph8ter

This is most of the issue. Shimano did say a 14 tooth max for their front derailleur but has since changed that to 15 teeth with the offering of their own compact front crankset. I myself just built my new bike 2 days ago with the guidance of my favorite LBS wrench. It's got an Ultegra front derailleur and an FSA SLK compact (50/34) crankset. There are no shifting problems either.

It is a TINY bit slower to shift into the big ring than my wife's Ultegra standard double (53/39), but there really isn't enough difference to talk about. I always try and 'let up' a little when shifting (it's just easier on parts and rider) so that may have something to do with it.

If you still need the lower gear but are worried about the 16 tooth drop, you can run a 50/36 instead. It's only 14 teeth, so in theory the chain should climb better between the small and big rings. Hope this helps and good luck!

SteveE

I think that the compact crank may not be a good option if you have a lot of short climbs that require you to use your small chainring. This isn't a problem with longer climbs but I could see how it could become a nuisance if you needed to shift to the small chainring a lot.

'nother

. . . which, at 50/34, also has a front tooth difference of 16T. There is enough "play" in the specs. Furthermore, even Shimano claims that no special FD is necessary for their cranks. People have been using regular Shimano FDs on 50/34 compact cranks for a number of years now with no problems (provided that they are adjusted properly but that applies to any FD/crank, not just compact).


This is probably the best route. As SteveE and Retro Grouch said, some people find the drop from 50 to 34 very drastic, so if you're shifting between the large & small rings frequently, it might feel a little odd and you may have to compensate by upshifting on the rear. But with a 50/36, this is less drastic, and using the existing 12-27 cassette gives you a low gear of 36x27 which should be plenty low enough for all but the steepest of grades.

roadfix

As suggested above, that's probably why some riders prefer the 50/36 compacts instead of the 34.......or even 48/36 combos.

Actually I wouldn't mind running a 48 big ring (like my tour bike) but my current setup doesn't include an 11T or 12T cog so that's not going to work.

TheRCF

On my present setup, I can usually leave it in the big ring for a "Normal" trip. Even the steep hill when I start is short enough that, if I stand up, I can make it without shifting to the small ring, but I wouldn't want to!

But there are some hills I have started to take on - typically 1 to 2.5 miles. That's where I really need a lower gear capability. I don't have to ride those places, but I do them to try to get stronger for the normal hills (I'm not a good hill climber).

TheRCF

> But with a 50/36, this is less drastic, and using the existing 12-27 cassette gives you a low gear of 36x27 which should be plenty low enough for all but the steepest of grades. <

I don't know how steep my hills are compared to what some people think of steep, but I do know I'm not very good at them!

According to my topo mapping software, the hills I climb are typically 8-11% grades average. Of course, some sections would be much worse than the average. Distance usually is between 1 - 2.5 miles.

SteveE

In those cases you're not constantly shifting. Assuming an average speed of 10 mph on these hills, you're talking about 6 - 15 minutes in the small chainring. In that case, I don't think it'd be a case of frequent shifting.

TheRCF

Boy, I wish I was doing 10 mph! More often on those steep hills (steep to me), I'm doing 3-5 mph. A lower gear may make that better, but I don't see 10 mph in me.

Even the part of Diamond Head I climb (0.6 miles / 3% average / 10% maximum according to the software), I will be under 9 mph and I guess usually I'll be around 6 mph. I can push it faster but only for a very short distance. Just not good at hills.

SteveE

TheRCF -

If it'll make you feel better, I only used 10mph because it made the math easier.

SteveE

gruppo

To use compact chainrings you'll have to swap out your crankset so I suggest you just install a triple (The triple/compact debate* is tiresome and a triple set-up will provide the gearing you need and shift just fine - it's a tried and true solution).

*The compact set-up has been around for decades, aka "cyclocross gearing", and works well in some applications, but a triple is still the best option for many folks.

TheRCF

As it happens, I just got an email from a guy I ride with who seems to be naturally gifted and he told me on a 1 mile steep hill we've both climbed he was over 10 mph on the steep part! That's one of the ones I'll be doing 3 mph and probably zig-zagging. He's been niding less than two years (I've been doing it just over 4). Course, he's less than half my age, but still, that's a heck of a difference.

TheRCF

My prior bike had a triple and certainly that approach would give me much lower gears, but every time I test rode bikes before buying the double I have now, the double crank ones just seemed to shift nicer. Can't really explain how it differed, but it did.

bbattle

My Orbea came with an FSA Gossamer compact(50-34). After some newbie-shifting training, I've not had any problems with it. I prefer it to the triple on my mountain bike. I'm on the big ring most of the time, using the small ring for climbs.

merlinextraligh

50/36 seems to fit in the why bother category. You can get a 38tooth inner ring on a 130 BCD crank (I run a 53/38 on FSA K force) 38/27 is a gear inch of 38, 36/27 is only 2 gear inches lower. If you think you need a lower gear enough to get the compact, I'd get my money's worth and go with the 34.