Change to 11-30t cassette with short cage

[Ribena75]

I want to swap out my current 11-28t cassette (9 speed Tiagra) for a 11-30t - will the short cage handle this?

[The French Tandem]

According to Mr Shimano, the largest possible spocket with your derailleur is 27t. Pushing it too far by 1 tooth is probably acceptable, but 3 teeth might be a bit too much! Make sure you do not exceed the total capacity of 29t (=big ring+ big sprocket - small ring - small sprocket)

A

[sojournermike]

I’ve run a 7900 rear mech with a 12-30 cassette (10 speed) and that was fine. I’d try it and see what happens. Possible issues include b screw not long enough (I think unlikely), shift quality deteriorating as parallelogram is intended for narrower cassette and not enough chain wrap capacity (big enough chain for big big leads to overly slack and falling off chain on smallish cog and small ring). Otoh, it might work perfectly acceptably.

If capacity is a problem I’d prioritise big big, as accidentally selecting that combination with a too short chain can do plenty of damage.  It being able to use the smaller cogs in the small ring doesn’t really bother me. (There is an exception in that were one daft enough to have a 53/36 chainset and 11-30 cassette then DI2 in sequential shift mode will allow you to avoid the bad combos... but that’s a special use case!)

[Ribena75]

Thanks. My main reasoning for this was to make the hills on The Shark 200km more bearable, but turns out I cannot go now. Also I cannot actually find a 11-30 cassette. I've a new steed on order with a ton of low gearing options anyway, so will leave the Ribble agony wagon unfettled, for now!

[Davef]

I’ve run a 7900 rear mech with a 12-30 cassette (10 speed) and that was fine. I’d try it and see what happens. Possible issues include b screw not long enough (I think unlikely), shift quality deteriorating as parallelogram is intended for narrower cassette and not enough chain wrap capacity (big enough chain for big big leads to overly slack and falling off chain on smallish cog and small ring). Otoh, it might work perfectly acceptably.

If capacity is a problem I’d prioritise big big, as accidentally selecting that combination with a too short chain can do plenty of damage.  It being able to use the smaller cogs in the small ring doesn’t really bother me. (There is an exception in that were one daft enough to have a 53/36 chainset and 11-30 cassette then DI2 in sequential shift mode will allow you to avoid the bad combos... but that’s a special use case!)

Are you allowed 53/36 ? I thought a 53 always came with 39 as a difference of more than 16 less will cause the universe to implode.

I occasionally have a 53/39 with an 11-34

[sojournermike]

I bought a 53/39 for ‘little money’ and swapped the 39 for a 36. Actually I could try running 39:30 as it’s not dissimilar to 36:28, but given I live on the edge of the Yorkshire Dales and Moors I quite like having a slightly lower gear, wimp that I am;)

There’s a bit of leeway available.

[CrazyEnglishTriathlete]

I had a similar situation unwittingly on my race bike.  I thought it would be a good idea to drop down to a 13 - 29 rear cassette to go with my 53-40-30 triple, so that I would be able to get up pretty much anything.  The investment paid off - it was probably the only reason I got up Bwich-y-Groes after 300km on the Cambrian 4C, and that gruesome top 2km of the Col du Glandon.   My race bike has been stripped down to steel, repainted and rebuilt by Argos Racing Cycles, who pointed out that Mr Campag recommended a long cage and the current set-up was at risk of sending the rear-mech into the wheel and the slight clicking in the granny gear was that sound of impending doom.

It didn't happen in the 6 years I rode with this set-up (and I never heard the clicking when I dropped down to that 28" ratio as I was more worried about maintaining snails paces up tarmac-defying inclines) but I have secured a long cage rear mech at astronomic cost through the wonders of eBay as even at the price I paid it is cheaper than a new rear wheel.

[iandusud]

I run a 11-32 10speed cassette with a short arm Ultegra mech rated up to 28t. It works but chain length is critical. I would expect to get your set up working with a 30t at the rear. IME Shimano gears are quite forgiving of being run beyond stated capacity.

[Ribena75]

Turns out I actually have a 11-25 cassette on there! I will upgrade to the heady lows of 11-28 when its due a change.

[Tom7]

I have a 5700GS rear derailleur on a touring bike. I fitted it as I built the bike up as it was laying about. It exceeds the 22 tooth difference by another 6 teeth and has a 32 tooth lower gear on the cassette where 28 is the limit. Yet it works well enough that I haven't changed it after 3 tours and 5 years.

I wouldn't recommend it but it works well and shows the rules for derailleurs are guides.

[Adam]

Just fit a derailleur hanger extender - less than £5 - and then it won't matter about the short cage.  I've gone from 28 to 34 teeth with a short cage after fitting an extender, and the gears work fine.

[rogerzilla]

I made it work with a very short DA rear mech.