How long in theory should a shimano XT 9 speed rear cassette last, average 90-ish miles per week.

It depends on too many things to give an accurate answer.

What surfaces you ride on? Do you wash your bike after every ride? Use a chain bath? Keep it well lubed? Even then its pretty impossible to give an answer.

Most people don’t ride theoretically.They last until they wear out.Depends on where you ride,how you ride,how you look after your drivetrain,what lube you use etc.More than 6 months-less than 5 years.

How often do you change your chain – do you own a chain measurement tool?

As a guide I do your kinda mileage off-road, and my (XTR) cassette has just died – had it over a year, and probably on its 5th chain.

I thought it was a bit of a long shot, I clean and lube every other week, and when it needs it eg after muddy rides with finish line wet lube, spray regularly with gt85. I ask because my chain snapped, both chain and cassette were replaced by LBS, both only two months old, understand that chains do break.

understand that chains do break.

/thread closed

I broke one after 200 yards. It happens.

Can wear out a cassette in a few hundred miles easily if they’re particularly crap!

If you are going through them at that rate I would suggest that you buy some tools and learn to change chains yourself. If you can fix a puncture and use the internet, you can change a chain. Then you can decide how shagged the cassette is.
As suggested a chain checker is your friend and I’m not to keen on GT85 instead of chain lube.

Matt24k +1

Points taken, I would never use GT85 instead of lube, only in addition.

just use lube as the solvents in GT85 will wash out the lube.

By all means use GT85 to clean it off the bike and then allow it to dry and lube it but some lubes – eg the water based wax won’t like that and would prefer it if you use a normal degreaser which doesnt leave a residue.

I use Rock N Roll lube for off road bikes. Seems to work well. GT85 should never be used as lube.

I have also found Finish line green wet lube to work very too.

Chain checker is *the* best spent money on a bike. Cyclo ones are only a fiver.

And GT85 is the devils jizz.

I run a couple of cheapish chains on each bike, and swap them over each time I clean them. If you change them for a couple of new ones when they reach 0.75% then you’ll easily double the life of the cassette and chainrings.. After all, an xt middle chainring is easily more costly than 4 chains.

My XT 10 speed Chain and Cassette have lasted approx 12 months 30-60 miles a week all weathers lubed before each ride and washed off after with fenicks or the like, then left to dry 😯 then lubed before I go out the rust on the chain soon blends in. 😀 its completely knackered now and in the bin, but always changed gear and never slipped.