The front tyres on my Volvo XC90 were down to 2-3mm whilst the backs were at 4-5mm. I therefore changed the front tyres and had the front tracking done. Since then, I've done about 300 miles and the vibration coming through the steering is worse than before I changed the tyres. I know that the rear offside tyre was at 4mm whilst the rear nearside tyre is at 5mm. I was told the rear tracking may be out. Should I replace all four tyres at once and get specialist four-wheel drive alignment at the same time to solve this? If not, what do you suggest I do? Could the rear tyre misalignment have a worse impact as a result of the front alignment being done?