good point.
and beyond the safety concern, I was surprised at the weight difference between tires. Ever curious, I weighed a Zaffiro (about 38g) and another tire selected randomly from my large pile of discards. It was half the weight (about 20g). OK, so that's only.... a fraction of a 9kg bike but still, I guess it adds up. Ditto wheels where there are real weight savings by upgrading. (and I understand a gram saved in wheels is worth some multiple of a gram saved elsewhere.)