One of the most striking differences in the approach to certain things that my dad and I have, is that I will favour the more factual, logical route (as Fox is demonstrating he also does in this thread) for coming to conclusions, and my dad will favour objective opinion.
An example...
My dad once drove a Mondeo ST TDCi. I think that week he'd been mostly driving a 1.4 Fiesta. We got talking about how fast the ST TDCi was... his friend, who owned the car, had made amazing claims about performance and what he'd out-run in it. My dad, after driving it and feeling the torque, believed those claims. He offered up that it was "faster" than my 330. No matter how many figures I pulled up... the 50% power advantage, the benefit of RWD, the 2 second shorter 0-60, the extra 20 mph top end, the 50/50 weight distribution.. he wasn't having it. Opinion and claims of a friend overrode all fact and logical reasoning.
Tyre tests are a similar thing. Most people who are fitting your tyres... are not very clever. I say most, as I'm sure there's a guy with a PhD in Astrophysics that is fitting tyres in some remote Buckinghamshire village. The fact remains that the chances of your tyre fitter or random friend or even one's own opinion, being of more factual value than a controlled performance comparison, are pretty slim.