Rear cassette. How big can I go?

davescott100

100 µW
Joined
Sep 11, 2016
Messages
8
Hi there

I would like to change my rear cassette for better hillclimbing and I’m after some advice. I have a bog standard, I’m sure very old, Shimano Deore derailleur and a 11 - 32 cassette. I would like to change to a 11 - 42 tooth. Does anyone know how big you can go before you need to change a standard derailleur?
 
Your derailleur probably will do 34t, maybe 36t, definitely not 42t. You can either get a different derailleur or use a drop hanger to lower your derailleur and clear the big sprocket.

s-l400.jpg


Note that this will likely make your shifting worse at the small end of the cassette, by increasing the distance between jockey pulley and sprockets.

Also, if you use a big heavy cassette without also using a clutched derailleur, inertia in the cassette can spool slack chain over the top when you suddenly stop pedaling. Your derailleur can run out of takeup capacity, causing the chain to go slack in the small-small combinations. If you don't add enough chain links to wrap the big-big combination, things will break when you shift to that gear.

How many speeds do you have on your rear cassette? You can get 12-42t in 8 speed, but nothing that big in 7 speed as far as I know. 9 speed or more, there are lots of choices.
 
Thanks for the reply. Looks like there’s more to consider then I originally thought. I should probably get a derailleur with a clutch, designed to work with a large cassette.

I currently have an eight speed cassette. Driven by an old BBS01 250 watt. I would like to improve climbing without loosing top speed. Hence changing rear cassette not the front chainring. I’m on the verge of buying a BBSHD, so I’m looking for a solution that can handle more power and more speed.
 
Have a look at Microshift Acolyte 8 speed shifter, derailleur, and 12-46 cassette. It's the cheapest way to get into the wide range 1X drivetrain game, and it has the cost and durability advantages of 8 speed. Use a 42t BBSHD chainring, because if you go smaller the chainline will suffer greatly.
 
Chalo said:
Have a look at Microshift Acolyte 8 speed shifter, derailleur, and 12-46 cassette. It's the cheapest way to get into the wide range 1X drivetrain game, and it has the cost and durability advantages of 8 speed. Use a 42t BBSHD chainring, because if you go smaller the chainline will suffer greatly.

Well. Fitted and tested the Microshift Acolyte drive chain today. Really impressed. Definitely an upgrade. The only real drawback is the shifter feels a bit cheap and doesn’t fit in well with the other controls I have on my handlebars. Other than that, I’m very pleased. Gear changes are smooth and precise and with the new chain the whole thing is much quieter. I can now hear the slight wine of the motor! Thanks again for the suggestion Chalo. I am now climbing all sorts of rough, steep terrain with my 250 W motor. Great fun.
 
Building a Wild One 20" with BBS02 and found this thread relevant to the lessons I'm learning at the moment.

Had a Shimano XT 10 spd DER Med Cage on hand. Only handles a 36T max with 39T Chain Pull.
Added an 11-40 10Spd Microshift AdvantX Cassette and Risk Extender. Reaches 48T just fine with 2T leftover for Chain Pull.

8 gears work really well considering the added lag time between shifts on the largest 2 sprockets.
Bottom 2 gears skip due to the relocated DER geometry. Won't work with the XT.

Ordered the Microshift AdvantX DER & Shifter so after next week if I remember, I'll post an update.
 
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