I've had a bit of a rumble from one of the back wheels for a while and my local garage told me it was uneven tyre wear, not bearings or anything nasty, and that it was fine to carry on for a while before changing tyres.  That was a while ago and I have checked them regularly since.  Other than a bit less tread in one area than another it didn't seem anything to worry about.

I just did a 300 mile return motorway drive and was thinking about putting new tyres on before that but didn't get around to it.  Anyway, early in the trip that same tyre started making more noise and vibrating, especially noticeable at around 60mph.  At 50mph and at 70mph it was a lot less pronounced so I just made sure I didn't hold it at 60, but generally stayed above that, say 70-75.  

 

Got home and saw this:

About 3 quarters of the tyre is fine with legal tread:

One patch looks like the second photo - SCARY!

 

Now, the Ford Focus has quite heavy camber on the back wheels so it is not surprising that the wear is on the inside.  I can't believe that it wore through that much in just 300 miles though!  I am convinced that this wheel was not properly balanced when the tyre was fitted, and when I jacked up the wheel off the ground, it spun on its own until the worn part was on the top.  It has never sounded right but I just couldn't put my finger on it and maybe took too much comfort from the mechanic telling me it was ok.

This is a real lesson to me to make sure I get tyres looked at as soon as there is anything not normal happening before it ever gets this bad again.  Needless to say, it'll be a trip straight down to get a new set fitted before I go any further.

 

New Michelins now fitted on the back and I feel a lot better about it!

The tyre fitting place recommended getting the wheel alignment/geometry done, but I am not sure this was the problem.  The reason is that I had moved the bad tyre from front to back previously and the vibration and noise went with it so in my mind that indicates the fault is with the wheel/tyre rather than alignment.  Add to that the lack of weights on the rim (which might have fallen off or never been fitted) - would you agree with that?  I guess it can't hurt to get the alignment checked and adjusted, but its €100 I could spend elsewhere if it is not needed.

 

Wtf!?  I have never seen that happen before!! 

I've seen the whole edge wear through but just one little patch is really weird, interested to know how!

I wonder if that spot had a bulge on it?  Only seen bulges in the sidewall before but can't see how else it would happen.

I'd agree that is very odd wear pattern. I'm guessing the other tyre on the back is wearing evenly? 

Possibly a defective tyre?

The tyre on the other side had even wear, consistent with what I would expect, so this could have been a defective one.  I have read on the internet about a "saw tooth" phenomenon for back tyres on front wheel drive cars as they get dragged along behind (random link here http://www.continental-tires.com/car/technology/tire-knowledge/lex-1-3-1), and this can apparently cause some deformation (bulging or oval shape) of the tyre but all sounds a bit wierd to me - why this has only happened on this tyre and not the previous sets I have had over the last 120k miles?