As a recent convert to the darkside here’s my newbie question.
I’ve entered a particularly hilly sportive and think I’d want/need a different block on the back.
My current steed sports 11-25 gearing and I am considering fitting either a 12-27 or 12-30.
I’ve always been a masher on an MTB but trying to learn to spin a higher cadence on the road.
I’m leaning more towards the 12-30 set up.
If I do fit such a large rear ring will I need to lengthen the chain to fit or would I get away with keeping it the same as for the 11-25?
Thanks in advance for any advice or opinion.
TMS

You’ll definitely need to lengthen the chain for the 30.

Depending on the length of the mech it probably wont cope with such a wide spread.

.. I’d change to a compact on the front if you can.

You’ll probably have to lengthen the chain even if you just go from a 25 to a 27, depends on how much slack there is currently. I did the Whitton a few years back as a very raw road bike rider with an 11-25 at the back and it was fine, if a little harsh on Hardknott – compact chain-set – this year I went with an 11-27 and it was, slightly, easier. I guess whether you go to a 30 depends on how strong a climber you are. I’d say I was pretty average, but my local riding in the Peak is hilly, so I guess I’m used to it,.

What I wouldn’t do is fit a larger cog at the back and reason that you won’t ever go ‘big-big’ then end up tearing your mech off in a moment of absent-mindedness.

You don’t say btw, if you’re using a compact or a standard double. If the latter, a mate of mine stuck an 11-32 XT cassette and a mtb rear mech on for the Whitton a few years back and it worked for him. Looked horrible though 🙂

I’ve run an Ultegra mid-length-cage rear with 22-34-44f and 12-28r, but that’s as far as I’d push that length of cage.

Both my road bikes have 11-32’s on now, and both have long cage XT mechs as a consequence. Going to 27 might be doable on your existing chain, but going up to 30 almost certainly 😉 won’t be.

50/34 on the front and 11-28 on the rear for living in the lakes 🙂

11-34 on my road bike with XT long cage. 53-40-30 up front. Lovely having the range.

what mech at the back?

road ones probably can’t (officially) clear a 30t cog. 12-27 or 12-28 should be OK normally, depending on the difference up front.

Put it this way, if your bike’s set up right then if you add teeth, you should add links. But is it?

The other thing though is that it depends a bit on the operator- even if you run out of chain in the crossover gears, that only matters if you use them, so as long as you only use the lowest gears in a smaller chainring it ought to be OK. Personally, that doesn’t work for me, sooner or later I’d shift down in the big ring into a bad gear.

OCB – Member

I’ve run an Ultegra mid-length-cage rear with 22-34-44f and 12-28r, but that’s as far as I’d push that length of cage.
Both my road bikes have 11-32’s on now, and both have long cage XT mechs as a consequence

similar here here glad to here not the only one except run a “touring mtb triple” 24 36 48 Long cage XT and 12-34 with 700c 32mm and 11-32 with 25mm tyres – it looks ugly but you can ride up anything and if you spin out it means you can relax and look for a beer stop

probably worth replacing the chain if you switch the block unless it is really new and funds are very tight

I put a 12/30 cassette on my trek madone 6,9 for the Dragon ride as I felt that I could use some lower gears but I didn’t want to change from my 53/39 chainset.
The cassette ran perfectly with a short cage Ultegra DI2 rear mech without lengthening the chain.
The cassette also runs perfectly on my Cannondale Super6 with a Dura ace short rear mech.
A friend tried one on his Specialized Tarmac SL4 with SRAM Red short mech and it wouldn’t work.

I think latest generation 105/ultegra short mechs are good for 30t and mid up to 32t.