Cassette Conundrum!


Senior Member
Isle of Wight
Hi all,

I currently have a 9 speed 11-25 cassette and a 50-34 compact chainset on my bike.

I'm off down to Provence at the end of April / early May and part of my week will include a ride up and over Mont Ventoux. Having sought advice elsewhere on this forum, I am going to fit a cassette with a lower bottom gear to help me to the top of the climb. I think an 11-28 will be OK and I'm presuming a straight swap over won't cause any issues, but I'd appreciate the advice of my learned friends on here.

My rear mech measures about 75mm centre to centre of the guide pulley's, so is this likely to be a short cage, and if it is, can you guys confirm that it will work OK with the 11-28 cassette? If I'm really pushing my luck, would it be likely to work with a 30 tooth large sprocket too? I'm not looking to replace the cassette and go to the expense of a new mech and chain just for the extra insurance of a 30 tooth, so if it would need all this I'd probably just settle for the 11-28.

Any advice will be much appreciated, thanks.
I have a 5700 short cage derailleur that runs with a 12-30 cassette.
I'm running an 11-28 on both my road bikes at present. It's a good choice, and both my rear mechs are short cage. I moved to 11-28 from 11-25, the difference on steep hills is actually more noticeable than I'd imagined.


The older I get, the faster I used to be ...
My Tiagra rear mech is 55mm c to c jockey wheels and I'm running a 30T rear with 50/34 no problems.
edit - if you have 78mm suspect you have a 'long' cage GS (?) mech anyway.
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You might still need to swap the chain anyway depending on how long it is just now , if you ever went into 50/28 with the new cassette it might jam depending on how long the chain is now , you would need to put the bike into 50/25 then see how many links you have spare before the derailler is pulled straight , you need at least 4 extra I would say to put on the bigger 28t cassette .


I've kept my 116 link chain, with an increase from 25T to 28T I've still got enough room to spare.
Will depend how its set up to start with , I just add 2 links extra so if I went up an extra 3 teeth my chain would not stretch to the biggest cog which I found out when I replaced my 12/15 with a 12/28 .
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