peter3197, on 02 Feb 2014 - 06:59, said:

It's your funeral, but unfortunately it could be someone else's as well. I am sure that insurance companies and the police look very carefully at the circumstances of accidents where the car has a wheel/tyre fitted that is not the same as the others. Handling, in all its forms, is severely compromised when you have a different sized wheel/tyre on one corner.

a steel wheel wont make your car handle differently when it uses the same sized tyres



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I think you will find that the last line of my post states clearly that a different size wheel/tyre on one corner would compromise the handling, however the use of a steel wheel that is not the same size as the other wheels but with the same size tyre on it as the other wheels will affect the handling but not necessarily to an extent that would jeopardise normal use. The flex of the tyre on the wheel changes with the width of the wheel and, if the tyre is too wide for the wheel, the tyre can come off . Your local tyre place will tell you what size tyres are acceptable on what width wheels. 

The Construction and Use regulations for cars state that if one tyre on a ''axle' is a different size to the other tyre on the same 'axle' then the car is limited to 80kph (50mph) and the different size tyres can only be used as a temporary measure in an emergency (e.g., after a puncture).

 

So the front tyres must be the same size (225/45-17, etc.) as each other and the rear tyres must be the same size as each other or the above restrictions apply.  Simple.  Whether the wheels are steel or alloy is irrelevant.

peter3197, on 02 Feb 2014 - 06:59, said:

I think you will find that the last line of my post states clearly that a different size wheel/tyre on one corner would compromise the handling, however the use of a steel wheel that is not the same size as the other wheels but with the same size tyre on it as the other wheels will affect the handling but not necessarily to an extent that would jeopardise normal use. The flex of the tyre on the wheel changes with the width of the wheel and, if the tyre is too wide for the wheel, the tyre can come off . Your local tyre place will tell you what size tyres are acceptable on what width wheels.

There is no danger or tyre coming off wheel its the right size. Being a mechanic you can kinda tell whats acceptable.but you were not too know