Short or Medium Cage Shimano 105 5700 Rear Mech for 30T Cassette?

Updated 12 April2015

Do you need a medium or long cage rear mech to run a 30T Cassette? This was the question I asked myself recently. We're going to the French Alps for our Summer Holiday this year. Whilst I hope to be properly bike fit I am really keen to make sure that I can ride all the climbs - including the difficult ones like Mont Ventoux - without running out of energy and failing.

I normally run a 11-28T cassette with a compact chain set (as I am old!). Until last year I had never failed to get up anything using this gearing - although I failed on Hardknott Pass. I saw that as an aberration but  recently (March 2015) I failed again on Rosedale Chimney and Boltby Bank. Whilst these three climbs are special cases with very steep sections it just shows that if I'm over geared I know I am lining myself up for a failure. The climbs in the French Alps are quite different in that the gradients don't reach over 25% but the challenge is in the length - which can be 20km in some cases.

I was not as worried about the gradient but more about the duration - for example I am estimating 2 hours for Mont Ventoux. The backup plan was therefore to lower the gearing and the option was a 30T cassette. However 28T is the biggest for 105 (5700), and so the option is Ultegra where a 12-30 is available. Until last year the word "Ultegra" would mean a non-starter on cost grounds. What has changed is the introduction of Ultegra 6800 and 105 5800 ranges - i.e. 11spd. This has meant that Ultegra 6700 (10spd) is now more affordable (although not cheap). So I ordered a 12-30T Ultegra 10spd cassette.

The next challenge was whether or not my 105 5700 rear dérailleur (short cage) was up to the job of managing an 18 tooth difference across the cassette (although only 1 more than needed for an 11-28). I do have a spare medium cage 105 5700 rear dérailleur so if the short cage would not work I had a fall back plan.

The voice of the internet on the question of short or medium cage is fairly evenly split between short cage so the only way to really see was to try it.

First I photographed the 11-28 cassette on 28T in both the 34 and 50 chain rings:

34-28

50-28

This set up has worked very will for me for many 1000's miles so I am fully satisfied with it.

I then removed the 11-28 cassette and fitted the 12-30. The biggest issue is probably the big-big combination here:

50-34T

In big-big the dérailleur is on the limit and I would not use it. I occasionally use the big-big with the 28T cassette but only for a few meters at a time as the chainline is poor. It shows that with the 30T cassette I need to make sure I never go lower than the 2nd gear.

In small-big (the one I want for the Alps) it actually looks OK. In this picture I have adjusted the B Screw by about 3 full turns tighter to pull the jockey wheels away from the cassette and after this all was fine. The photo does not show it but these few turns made all the difference

34-30T (B Screw tightened)

Having fitted the 12-30 cassette all gears can be selected smoothly and without snatching or slipping, when using the work stand. This includes front ring shifting both up and down in all the most likely combinations of gears on the cassette.

This gives me a lot of confidence that all will be fine. I might be at the limit but as long as I am careful I see no issues.

 
The next steps is to actually ride it on the road - so all this review can say at the moment is that all is fine on a work stand. I'll report back when I have ridden it.

Updated 12 April 2015 - I have ridden the bike a few miles and can report all is well. More miles needed but I think all OK - just don't select big-big.

The good thing about this is I can fit the 12-30 before I go to France and then if its not as hard as I thought I can refit the 11-28 while I am there. I only need take the cassette lock ring tool and a chain whip