I have just noticed the front tyres on my2005 c70 convertible are different front to rear
the fronts are 225/50R16 92 W
tbe fears are 205/55ZR 16 91Y
is this normal
I have owned the car since new and the tyres were supplied and changed during service by an independent Volvo specialist

 

the 2005 didn't come to the US - is yours a gen 1 or gen 2? Assuming its the gen 1, both tires are correct for a C70 but the 205/55s were on the LT trim and the 225/50s on the HT (ie high pressure turbo) trim. There's no reason for a stagger in a FWD car and certainly not with the wider tires in the front...

 

The car is a 2005 UK specification so I’m assuming 1st Gen it’s a 163 BHP so I think Low pressure Turbo
so is this likely to be a problem ? I’m not quite sure what you mean by stagger

 

stagger refers to when cars have a different tire size front and rear. typically this is for RWD cars with lots of HP which need more width in back. Google the tire sizes for an Acura NSX for example but very few cars come out of the factory with two different sizes. based on your engine rating I'd go with 205/55R16 as the tire size all around and stick with the same model to retain balanced handling.