Have I shortened my chain too much?

peat

I put a few more teeth on today ahead of a trip to some big hills.
I sized the chain in the way I was shown at my LBS and a few online tutorials, but when changing from the largest sprocket downward, it seems to jam 1 time out of 3. (when in large chainring)

See pictures:

Large chainring, large sprocket:

Small, small:


The cassette is a 12-30, the size that origianlly came on my bike so i'm sure(?) the cage is appropriate.

Anything glaringly obvious in those shots?

mercia_man

Looks too short, judging by big/big pic, particularly if it's jamming, although that is not a gear you would generally use. I've always used a method recommended by Shimano - in big ring/smallest cassette cog, top jockey wheel should be vertically above the bottom jockey wheel.

Matthewfalle

Methinks that is far too short judging by the top piccie - no dramas though, throw in a quick link or two until desired length arrived at.

Job's a fish.

taon24

I'd have thought that you are right at the upper limit of the chain capacity (I'm assuming a 50-34 chainring). With a 12-30 cassette you are looking at a chain capacity of 34, which is beyond the suggested shimano short road dérailleur maximum of 29.
1 (or maybe 2) more chain links might be a good idea as the first picture looks too stretched, and the second not as flexed as the derailleur could be.
However one solution is just not to use the littlest two cassette sprockets with the little chainring and biggest two cassette sprockets with the big chainring. This keeps the chain within the stretch the derailleur can handle. You might find you can get away with this chain if you followed this solution, though I'd be worried you'd damage the rear mech if you accidentally shifted into big/big.

peat

Cheers.

Yeah, I'd rather have it 'right' in case of a panic-shift on a ramp.

With regards to cage-length - As I say, it came with that gear combo originally. I'm just wondering if the LBS changed the cage when i swapped to a 11-28 last year.

Annoying, a semi-expensive lesson.

keezx

Chain length is good.
Big-big makes no sense, never done it in 40 years, not even in the 5 speed times.....with 13-18

taon24

Peat wrote:

Cheers.

Yeah, I'd rather have it 'right' in case of a panic-shift on a ramp.

With regards to cage-length - As I say, it came with that gear combo originally. I'm just wondering if the LBS changed the cage when i swapped to a 11-28 last year.

Annoying, a semi-expensive lesson.

I suspect it will not be possible to get 'right' as you are at the ends of tolerances, so you may find with a chain length that is not too short for the derailleur in big/big that there is too much slack in small/small and it is unusable (the chain on the lower jockey wheel contacts the chain on the cassette, but you shouldn't be using that gearing anyway). However it is less likely to damage the rear mech than too short a chain, as it is at the moment.

jgsi

Peat wrote:

Cheers.

Yeah, I'd rather have it 'right' in case of a panic-shift on a ramp.

With regards to cage-length - As I say, it came with that gear combo originally. I'm just wondering if the LBS changed the cage when i swapped to a 11-28 last year.

Annoying, a semi-expensive lesson.

Fully behind you there.... it might not pretty, not clever, not being a proper cyclist and all that but there have been numerous times where I go big/big with a short cage mech ( but probably not with anything over 28t).

arlowood

taon24 wrote:

I'd have thought that you are right at the upper limit of the chain capacity (I'm assuming a 50-34 chainring). With a 12-30 cassette you are looking at a chain capacity of 34, which is beyond the suggested shimano short road dérailleur maximum of 29.

Shimano short cage will cope easily with a 12-30 cassette and compact 50/34 chainset. Have been running that set up for the last 3-4years on a range of bikes with no problem. The B-screw may need to be tweaked in some instances to ensure smooth running when you are in 50/30 - but I never run that and only very occasionally do I use 50/27
Clearly tho' you need to make sure that you have fitted the correct chain length to start with. I always use this calculator for that purpose and have never had a problem

http://www.epicidiot.com/sports/chain_l ... ulator.htm

buckmulligan

As others have said, you're just a link or two short unfortunately. You didn't say which method you used to measure it, but as always Sheldon Brown's guide is the best IMO.

It should work fine with a couple of extra links. The maximum capacity of the 105 5701 derailleurs are 34T for the short cage and 40T for the medium, neither are 29 as someone said above. I've been running the same 50-34 with 12-30 setup and 105 groupset with no problems.

Matthewfalle

Keezx wrote:

Chain length is good.
Big-big makes no sense, never done it in 40 years, not even in the 5 speed times.....with 13-18

Never done it? Ever? Nah. Me call Shibboleth.