Wheel / Tyre diameters

[JohnM20]

Does anyone know the allowed tolerances in overall wheel sizes between a wheel / tyre on one side of the car and wheel / tyre on the other side ? Looking at the skinny spare supplied with the car (2012 Mondeo) it appeared to be smaller in diameter but was this an optical illusion? It transpires that it isn't. I have just had two new tyres on the front wheels and the back tyres still have 4mm tread left. The difference in diameters is as follows:
New front tyres - 653mm dia. = 2051mm circumference
Part worn back tyres - 640mm dia = 2010mm circ.
Space saver spare - 630mm dia. = 1979mm circ.

The difference in circumference between the new tyres and the space saver is 72mm. Will this cause any problems other than the car will lean very slightly one way if I need to use the spare, especially if it is on the front ? I realise that there is a speed limit of 50mph with space savers.

Thanks in advance for any technical help that anyone can give.

 

[ProfJohnL]

Hello John,

I cannot conceive the car manufacturers would provide a spare tyre that actually caused a technical problem for the car. If there is a difference in diameter, it would be accommodated by the differential.

 

[Craigyoung]

The space saver is just a temporary fix to get you to a garage to get proper tyre fixed , its not supposed to be a long term fit , I felt the difference on our people carrier when our space saver was put on the other week , all of 2o minutes till I got it to a garage .

 

[seth1]

But one of the reasons for the limited speed of the wheel is just not because of the wheels speed limitation.Its not very good practice for the differential to operate in this manner, i.e with the power divider in the diff constantly spinning on its own axis,it makes it act like its constantly going round a corner and thus putting load on the planet gears and bevel thrust washers.

 

[JohnM20]

Thanks, Guys for your replies. Sorry this got put in the wrong section, it should have been in Technical. Perhaps the Mods can move it.