Thank you to everyone who gave me advice on the tyres…I finally have a solution.
I am having some problems with my chain jumping off when I’m jumping or riding very rooty stuff fast. I’m running 3×9 which I know is a little out of date, but don’t want to upgrade to 1×11 as I’m upgrading to full suss next year.This bike will be my XC bike. Can anybody help with this problem???

I used to use gear selection to stop chain jumping and never really had a problem with 3×9 – when on the bumpy stuff, select big ring front, low gear rear, increases chain tension.

Which ring is it generally falling off? If it’s either the big or inner ring, chances are that it’s your front mech range adjusters need re-adjusting. Also check chain length.

If it’s falling off middle ring to the inner ring, then look at your chain tension, it may be worn, or it’s a couple of links too long.

What condition are the teeth on your chainring? If they are really pointy, then the wear could also be a mitigating factor.

I pretty much always drop to 2-3 for these bits but it still jumps.

Rear mech tension springs may be worn? Just give your chainset some love, clean it, new lube, new cables. New chain too, and a cassette if it’s worn.

A couple of really good pointers there slackalice..I’m going to be fitting new tyres this weekend so will have a good look at those bits.

How can I tell if my cassette is worn?