Mixing crossply and radial tyres but not on the same axle

Question

We all know that mixing crossply and radial tyres is a bad idea. There are very few crossplys on the market now and no need to fit them. But those of us of a certain age are forever scarred by the public information films of their youth visualising accidents from incorrectly mixed tyres and are reminded of this whenever tyre damage is mentioned.

I understand the difference in construction of the tyres, and the effects of this construction on the individual tyre. It is quite obvious that mixing them on the same axle would be a poor idea. It seems as if it would make the car very susceptible to roll.

However, if I remember the films correctly, there is a combination of tyre mixtures which is legal. I think crossplys on the front and radials on the rear? Is that correct? Why is this combination safe, whereas the other way around it is not?

How is the handling affected in the two cases of axles with non-mixed tyres, but with different kinds on different axles? What is the underlying dynamics of the issue in such cases?

https://youtu.be/lrRz_ItWWDw

Answer 1

The legal combination (in many countries was crossply front and radial rear) this was because as crossply tyres approach the adhesion limit they give gently, unlike radial where it is all or nothing.

It was felt that most average drivers could cope with gentle understeer (crossply on front, radials on rear) better than sudden oversteer (ie with radials on front, crossply on rear).

Of course the petrol heads amongst us do engage with oversteer especially when dealing with snow - again a situation that can give the average driver a severe challenge.