I would love to have a definitive answer on this question. Through a lot of googling, my conclusion was a few mm between tyres wont make much of a difference or, we would all break our 4Matic cars when our front wore lower than the rears. Don't put 18's on the back and 17's on the front though with differing tyre sizes LOL.Would the same tyre rule apply to our 4-Matics as they would vary the torque transfer.
I know the expert advice is to put the new tyres on the rear but I've always strongly disagreed.
The vast majority of drivers will drive more steadily in the rain and will not be cornering any where near fast enough for the rears to lose traction.
What is a far more likely scenario in the rain is needing to stop quickly, like on a motorway with lots of spray etc etc.
In this situation 80-90% of the braking is needed on the front and that's where new tyres will make a big difference.
I think your third sentence is somewhat far from reality. So any slight deviation from going in a straight line will cause the back end to lose traction?? So nobody successfully goes round a corner on a wet road?Why would you disagree with *all* the tyre manufacturers, RoSPA, etc. ?
I follow your thinking, but in reality - your scenario above goes out of the window, as soon as you have some sort of sideways force.
In a straight line, yes, there is the vague chance that you will remain straight, and your front tyres might be called upon to do most of the braking.
However, in reality, any slight deviation from straight, a small steering angle, a slight sidewind etc. - will definitely cause the rear of the car (if the poorer tyres are fitted at the rear) to swing around.
It doesn't matter if its front wheel drive, rear wheel drive, all wheel drive, time and time again, this has been demonstrated, guaranteed to happen on a wet track or road!
But hey-ho - it's your choice!!