My rear tyres tread depth are not far from that of the fronts. I have done 9k and they average 6mm left. After all they are only dragged around - my Ford Orion rears lasted 80k and had to be renewed because the walls were cracking and likewise my Fiat Multipla rears lasted 8 years. Is the roomies suspension designed to scrub out the rears?

I have the same Roomie as you it is fitted with Hankook tyres. At 18.5K miles it had 6mm left on the rears and 4mm left on the fronts.

This seemed a very similar wear rate to that I had on my previous Fabia hatch and so far without the drumming noise from the sawtoothing from the Fabia's factory fitted Dunlops.

I found I got about 25,000 miles out of the fronts and about 40,000 out of my rears, I did about 160,000 with my roomy

 

I found the more load in the rear the worse the wear was, and if heavily loaded I noticed some feathering / sawtooth on the rear tyres outside edges

What tyre pressures are you running with, and have you owned the car from new and know for certain that the wheels/tyres were never rotated or just moved front to rear at a service by a technician?

Edited 8 June, 201511 yr by goneoffSKi

Had the car from new and tyres are pressurised to 2.2 bar front and rear