kicking tyres---
one should be able to feel the difference.
perhaps a bit subtle but should give a clue.
the only two flats i had, i didn't do the walk-around! both on 737's which have dual wheels.
and it was the push back crew that noticed the difference during push-back.
at least in San Diego, he said he had been trained to look for that and knew what a flat tire (US spelling) looked like.
the other was in heathrow and he wasn't as talkative about his experience. simply said it looked flat.
both indeed were flat.