Is there a temperature below which I absolutely mustn't cycle in shorts, even if it's going to warm up later? I don't really like wearing trousers (though I'm cycling in them now, because it is below freezing at night and only upper-mid 30's during the day), e.g. if it's 40 degrees, can I cycle to college (1.5 miles) in shorts, if it will be 55 on the return trip, or do I need to be a bit more patient?