I like to start cycling again but I have a steep hill to arrive at home so I would like to put a 42 teeth. I have an Ideal mountain bike model hillmaster with a 9 speed cassette. All videos on you tube show that I cannot install a 42 teeth on my 9 speed. Can I put the 42 teeth instead of the 32 teeth.

Thanks all,

  • That's quite a change percentagewise - 32 to 42 is close enough to 1/3 more teeth. Even a 35 tooth large cog will be 10% more teeth and a 10% lower gearing, and that might be all you need. Taking the hill a bit slower and pacing yourself might help too, its not about speed up, its about consistency.
    – Criggie
    Commented Jul 18, 2016 at 20:17
  • Hill climbing is common issues. The practical way to improve the torque are changing the smallest cog on the front crankset. Typical touring bike use 26T for smallest cog. Many change it to to 22T to prepare for long distance hilly trips (imagine you are crossing the Euro-asia highland). Here is some [bicycle gearing combination ][1] for your reference. [1]: bicycle-touring-guide.com/touring-bicycle-gearing
    – mootmoot
    Commented Jul 19, 2016 at 9:46

2 Answers 2


9 speed 11-36 is a common maximum cassette size.

42 would probably be too large for a 9 speed dérailleur to work reliably (Only 11 are specified to cope with 42 ). You would likely have trouble with the B screw adjustment, requiring a longer B screw or other hacks to get the dérailleur to clear the large cog. Even if you did succeed, the chain wrap would be minimal, increasing wear on chain and cogs.

You don't say what the chaining sizes are on your MTB, or your wheel size. A better option would be a smaller chain ring.


You can in theory, but you'd need a to have a 9sp cassette, optimally (which might be your biggest problem), and be compatible with the rest of your drivetrain. You might also need to replace the rear derailleur such that it has a longer cage, to give you more clearance between the cassette and the actual derailleur. This range, as it's known, will be listed in the derailleur's spec.

You might have trouble finding a 9sp cassette that goes up to 42T, but I'd be surprised indeed if you couldn't get a decent improvement on 32T.

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