Rego is due and the tyres on my DB1 have insufficient tread to pass. I have obtained a new rear tyre but it is hard as a rock and starting to crack. The nearest compromise I can find is a 120/70/16 for the front and a 150/80/16 for the rear. I am concerned the 150/80/16 may not fit the 4.5" rim. Any help gratefully accepted.