[Gaz64]

Warren,

I don't know current Fords, but I do know that with HSV you can get 245/35/20 on the Front, 275/30/20 on the rear.
Wider tyres on the rear, but near enough SAME rolling diameter.

I think with an ESP car, the tyres NEED to be the same rolling diameter.

I had one car years ago that would log wheel speed sensor codes for the rear wheels.
After many repairs guided by the manufacturer, it ended up being a software issue they were unaware of.
The wheel speed differences while cornering ( ie: roundabout) were too large, going outside programmed parameters.

On your car I would try same size tyres all round first to prove the exercise, but if the data shows differences at the moment, I don't know how you will get around it.