I have an AWD Smax, however, having purchased car secondhand (from dealer) about 18 months ago, I now need to replace rear NS tyre. On getting a price from local tyre garage they noticed there were 2 runflats on front axle and 2 standards on rear. 

They suggested that runflats should be replaced too as car not setup for runflats(I.e. ride/handling). That would mean having 3 matching new tyres & 1 old (approx 50% worn)

My question is can I have a mismatch of tyres? Do I need to change all tyres as it’s AWD? Is it ok to change worn tyre on its own or is it possible to change both tyres on same axle - all in view of wear on drive train. HELP!

Cheers

Are you changing it because it's worn out? I'd be more worried that side is wearing out twice as fast if so lol.

It's not ideal (but what is?). Personally I'd leave the run flats on till they wear out (it's a people carrier at the end of the day, not a race car). Does your car have TPMS installed (on the run flats especially)? Some people don't notice they have a flat tyre with a runflat unless the TPMS tells them.

I'd certainly change both tyres across an axle, not a good idea to leave 1 odd one.

Thanks. 
Tyre that I’m having to replace has a small cut in side wall so have no choice unfortunately, so not as a result of uneven wear.  Yes, have TPMS, but never had runflats before so all a bit new.

Do you think having new tyres on one axle & worn on other will have any detrimental affect on drive train? Some forums suggest this is the case as newer tyres obviously have a larger diameter & causes wear and problems with traction. 
Thanks for advice. 

It doesn't matter too much on Fords, they run 70%+ of the time on front wheel drive only anyway. The more expensive brands with more complicated AWD systems (Audi, BMW etc) need the tyres changing in pairs if not all 4 at once. 

I wouldn’t worry to much about the front tyres being run flats. I’d be concerned about the load rating, due to the smax weight, the tyres loading rating should be 102. The RF tyres might actually give you better feel through the steering wheel, due to the thicker sidewalls, giving less tyre roll under cornering. 

The 2 runflats on fronts have load rating of 98; Meta55 you’re right supposed to be 102. The car was sold to me with these on. 

1 hour ago, ESpring said:

The 2 runflats on fronts have load rating of 98; Meta55 you’re right supposed to be 102. The car was sold to me with these on. 

Take the car back and demand 2x decent front tyres. If they don’t want to play ball, there’s a whole heap of options you could take that would cost a lot more than the cost of 2x tyres.