Here in the Land Without Humidity®, 90º isn't hot. That's a "going about your normal business" temperature. Gets warm in the triple-digits, and I just start early or wait until late if it's going to go past 105º.
It seems like all of my particularly foolhardy cycling decisions have come on especially hot days. Spent 3 hours above 110º last July, drinking over 2 liters per hour. It was remarkably unpleasant.
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