thanks for the input, sreten.

I'm thinking it's not likely to have slid. the bike always seems to be in exactly the same orientation and location when I open the trunk lid as it had been at trip's start. in addition to the already mentioned layers of newspapers on the floor, there are bags of newspaper (perpetually 'on the way' to the recycle bin) and a couple of aluminum-and-canvas folding lawn chairs in there (in case a picnic happens) - all creating a sort-of nest for the bike - no room for sliding about. I suppose the bike COULD bounce up to the trunk-lid - and back down - but it weighs more than 25 lbs. wouldn't that take a mighty large bounce from the Buick? and cause considerable noise? an event I might be expected to have remembered? still a mystery! but I'll try the adjustment in tire pressure you suggest on the assumption you have other considerations for it than, apparently-specious, heat-related blowouts - I'm quite new to folder bikes and their teensy wheels so I'm open to good suggestions for improvement in any aspect of riding..