Depends on the spare tyre profile, might not be as bad as you think.
Use a tyre site that has a size equivalence/compare "widget" on it, e.g.:
http://www.tyres-pneus-online.co.uk/...ce-advice.html
Not sure what the tolerance is on Torsen (5% maybe).
If it's too far out just get a different profile tyre (used will do - plenty around at low prices) on the spare.
Personally I like my spare to be the same as the other 4, so both my cars have 2 sets each (summer/winter) of 5 identical wheels. Though the spares are usually a bit "tattier" and maybe not with the best tyres either. 
__________________
2003 D2 FL S8. Irish Green Pearl/Beige. Solar sunroof, auto-dim mirrors, electric rear seat functions and extended leather. Ski hatch retrofit. Aftermarket reversing camera. DVB-T and XCarlink now removed as redundant.
2016 Volvo V40 T5 Cross Country (4WD) with ALL the toys including adaptive cruise etc. etc. Osmium Grey with Blonde/Charcoal leather interior. Polestar performance "optimisation".  (Even rarer than a D2 S8!) Oh, and a brand new engine at just under 30,000 miles on the factory one! 
Finally: gone, but not forgotten.....
1998 D2 PF S8. Agate Grey/Platinum. Every option (I think) except electric rear seats, Tiptronic steering wheel, ski hatch, towbar & dimming door mirrors.
e.g. Cruise control, NavPlus/TV, Bose, GSM, Xenons, Solar roof, Parking sensors, Alcantara/leather everywhere of course.  (internal dimming mirror added later)
1998 (very early) Ford Focus 1.8 Zetec; ABS/TCS, Heated screen/mirrors, Aircon. Added Auto-dim mirror, Leather seats, Trip computer, Cruise control, OEM Ford SatNav with CD changer.
And before that a lot of Rover 800s, a few oddities, a lovely Triumph Dolomite 1850HL with Overdrive and way back in my schooldays an Austin Seven aka Mini 850!
|