We put the normal tyres back on again as the snow seems to have finally given up. The winter tyres were on for almost 6 months this time. The summer tyres were all set to the recommended pressures according to the label, 54 front and 52 rear and tested when cold.
On the drive up to Snowdonia yesterday the tyre pressure warning light came on. I stopped where safe and checked, no obvious flat and all the tyres looked OK. Checked with a proper dial type tyre gauge. They were all about 6 or more lbs higher than previously. Presumably from the drive and the hot weather. At the end of the drive I left the van for a few hours and checked them again and they were more or less back to their previous pressures. The same thing happened on the way home today but it was the offside tyres that were most affected. Again after a few hours they were more or less back to normal.
My temptation is to not rely on it so much now. The temperature was only up to 20C so what effect does the far hotter European temperatures have and doesn't it make the warning light on the dash being of much less useful?
Here is a humorously written article about summer tyre pressures with some serious advice. I'd be interested to hear from continental members if their pressure warning lights go off all the time.
https://www.cartalk.com/content/summer-driving-tips-6