"Take the weight off their feet", according to Michelin...

http://www.michelin.co.uk/tyres/learn-s ... rage-story

Fwiw, I've had to replace tyres on cars which have been left standing in one position for too long; crazing/cracking of the rubber surface occurs at the edges of the contact patch, just where the sidewall experiences most deflection.

Ken - I am sure you are right (and Michelin too) and what you (and they) suggest is definitely best practice.

But I wonder how big a problem this actually is in reality, as opposed to the need for tyre manufacturers needing to cover their arses against accidents that might occur in that first ten miles before the tyres warm up and the flat spots disappear.

My own limited experience is this: I acquired a 2CV (that Charleston below) that had been left in its (unheated) garage for eleven years, and not moved at all in that time. All four tyres were very nearly flat.

I pumped up the tyres and to my surprise they held air, and I used the car a bit without anything unpleasant happening. I replaced the tyres as quickly as I could, however, NOT because the flat spots were apparent, or dangerous in themselves, but because the tyres were at least fifteen years old and that's well past their sell-by date - they just couldn't be safe after that length of time.

I did a bit of Google "research" and it does look as if the problems are more likely to exist with high-performance and low-profile tyres. Not what I'd call the tyres on a 2CV.