Derailleur Length

Hi All

I love cycling but know nothing about bikes.
I own a Cannondale Supersix HM Ultegra DI2 Disc 2020 bike which I have been told had a short/medium cage derailleur.

My plan next year is to do some long and steep climbs so wanted to put a 32 cassette on the back to help up some of these.
I have been told I would need a long cage derailleur to do this so my question is, if I had a long cage derailleur fitted, can I use it for both a 32 and a 28 cassette?

I have two pairs of wheels…the ones with a 28 cassette on the wheels I got with the bike plus an older set of Hunt wheels with a 28 cassette on them so would love to just be able to swap the wheels over to change the gearing I have. I just don’t know if this is possible or not.

Can anyone help?

Please keep your answers really simple and I’m a complete numpty with technical info :stuck_out_tongue:

Thanks in advance


Yes a long cage rd will handle both. Your short cage probably will too. I would try it first with a properly sized chain before you upgrade

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Shimano are conservative (with a small ‘c’) with their recommended maximum ranges. You’ll certainly be fine if your derailleur is a medium cage and comments suggest you’ll also be fine with the short cage. There are claims that you can go to 40T with the medium cage but there was no indication of whether that was on a 1x or 2x chainring system.

There is no long cage Ultegra Di2 derailleur BTW.

You might need a new chain as well - going up a couple of teeth is usually OK, going up four is pushing it - plus the chain and cassette will be “mated” in that they’ve worn away together.

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Maybe have a look at this.

  1. Medium cage will do it fine, a short cage is officially rated to a maximum 30t cassette, but most people find they can go to 32t. di2 (unlike mech) derailleurs are expensive, so if you can use your existing one, that is good.
  2. Assuming (1) above you will be able to run either cassette. You will however need to adjust the B tension screw.
  3. Get a new chain, and size it for a 32t cassette. You can run that with a 28t cassette, but running a 28t sized chain with a 32t cassette risks ripping the derailleur off if you accidentally put it in the big-big combination.
  4. You should also update the ratios in the di2 e-tube software when you change cassettes.

I run di2 with a 30t cassette, and swap to a 34t cassette for the summer when I regularly do long climbs in the mountains.


Thanks for the link.
Plan to look at exactly what length derailleur I have (seems surprisingly hard to find out) and will look at this as an option if I have a small cage version

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Thanks for the detailed reply :slight_smile:

I will need to look at how to adjust the B screw but I’m assuming it’s just turning a screw and working out the ideal tension at the time of trying?

When you say update the rations in the e-tube software (that I didn’t know existed), is that just a quick 2 minute job?
I ask as I am thinking (next year) of using two different wheel sets with different cassettes depending on the type of riding I do. I may need to change this on a fairly regular basis so hoping to do what you suggest are simple changes that even an idiot like myself can do quickly.

I agree with the above, the 32t will likely be ok with your read mech. You can run into problems with cassettes larger than that because the rear mech must be large enough to hold the extra chain length needed to run the larger gears. I run a 32t with ultegra 11 speed di2 and its been great. most of shimanos newer rear mechs are designed for larger cassettes.

Hi there

I checked my bike and actually have a 30t cassette so was hoping I could get a 34t on the bike (as that’s what’s on the wheels from my previous bike.
Do you notice much difference between a 30t and a 32t cassette do you know please?
I was looking for a granny gear in case my legs fell off the wagon but maybe I just need stronger legs to get up the long or really steep climbs

34 might be a bit tough, are yo uable to post a picture of your rear mech? I have an 11-32 on the back with 52/34 in the front. I went with the smallest chain ring i could fit in the front so i would have a granny gear of 34/32 for longer rides and not cook my legs on longer climbs. :slight_smile: Its made a huge difference for me, I highly recommend it.