Mark My gut feeling is to say stick the space saver on the back, my reasoning being that all the 'work' (steering, power delivery etc) is being done by the front wheels and 70 miles is a fair way to go on a space saver. Alternatively, after having to swap a wheel on the motorway, in rush hour and torrential rain a few years ago, I bought a tin of tyre repair stuff that you just feed into the tyre via the valve. I'd be happier driving that distance on a full size tyre filled with that rather than the space saver but I can't give you any good, sound, mechanical reasons for it :) Dave