Bike feeling unstable on back wheel

Ive been riding to and from work every day this week. The bike has been making its usual creaks and squeaks as Ive been riding it, but as the week has gone on Ive got one problem that has been getting worse.

The bike has started to feel very unstable on the back wheel. When riding round corners (while pedalling) the bike has become quite loose and Ive nearly binned it a few times, with the back end sliding right out and slipping. When riding in a straight line it feels like the back end is pushing slightly out to one side. At first it was only when I made harsh turns but now its doing it with slight movements

I know the wheels could do with a little truing so would this solve the problem or is it something else?

The rear tire has a good amount of air in it and feels quite firm (although it does squash out a bit when I get my fat arse in the saddle)

What bike is it ?

FS or HT ?

Check that the QR is done up properly, and not damaged.

Check that the rear axle isn’t broken or cracked.

Check that there is some tension in the spokes.

Check that the back of the frame isn’t cracked.

Had that feeling in the back of my bike a few times, and it’s been one of the above. Otherwise, your tyre might just be knackered.

Its a FS.

Ive checked the QR as that was my first thought but its done up nice and tight.

Ill check the spokes as Ive had an issue with the rear mech throwing the chain off the cassette so it might have damaged some spokes.

I’d strip the hub down, could be cones working loose as well.

low psi tyre squirm on the rear is horrible, had it today with a slow puncture, it could be that, 30 psi will feel fairly hard for a lightweight but a large bloke will make it squirm all over the place

Suspension bearing or shock bush.

When my bushings were on the way out, the back end felt all “wobbly” when cornering hard.

or you might just need to tighten up the lock ring on the cassette?

bastard bastard bastard bastard

frame is cracked on the swinging arm

shit

unlucky, but at least you’ve not been dumped under a lorry by it

pics?

Ill get some tomorrow.

The crack is on the chainstay where there is what appears to be a crossbar just behind the seat tube. The crack runs right through from the top to this cross bar and is the width of the whole chainstay…crap description I know.

What make of frame?

Trek Fuel. 2005 I think

Commencal.

Photos for those that are interested