[Rubbond]

Dear Greg, Stefano,
Isn't the EU wonderful?
I keep trying to avoid getting into discussions on subjects about which I
don't know enough.
As a general rule I would say it's wise to stick to the manufacturer's
recommendations on tyre sizes and pressures, but obviously choosing tyres
gets trickier if the manufacturer was unaware of the advent of radials when
the car was designed.
Recommended tyre pressures are based on achieving the correct footprint on
the road surface. So if the weather gets hotter, you would need to let out
some air to get back to the recommended pressures. Radial tyres should never
be driven underinflated, but because of their better shape retention, a
certain degree of over inflation is quite acceptable. It doesn't change the
area in contact with the road anything like as much as it does with crossply
tyres. So you should actually be more careful with tyre pressures when the
weather turns colder. With crossply tyres, correct pressure is not only
important for grip, but also for tread wear.
Regarding the insurance issue and legality. I would call someone else's
insurance company and say you are just "considering" fitting taxi tyres....
And in the UK, I wouldn't start a discussion with the MOT examiner if you
already have....