Using the 60 threshhold would mean I hardly ever get to wear shorts. The average July temperatures where I live are 56 for the low and 72 for the high, although the sun rises very early, so it will probably be warm enough by the time I get out. That rule would restrict shorts for every day wear to July/ August, with the range extended to June-September for an afternoon jaunt. The May high is 63, but there's be too much risk it wasn't above 60 all day. Personally, I would feel thoroughly miserable and hot cycling in a pair of trousers at 59 degrees.
Aren't the legs also where the heat powerhouse is? They're doing all the work. 60 is barely below room temperature, so combined with vigorous exercise will generate a lot of heat. Also surely sweat soaked trousers will remove heat more quickly than dry air thus increasing damage Please don't tell me the damage I did that morning I cycled in shorts at 35-40, because it would be 50-55 later.
Sorry to offend anyone on here, but 60 is nowhere near the region I was looking at when I posed the question. Can I have some more realistic answers please?