It's already hitting 110 degrees F in Phoenix. Riding in the afternoon can cause heat stroke, there's no "getting used to it". Every summer one or two trail runners die thinking they can handle the heat while they attempt to run up Camelback Mountain. Even with proper hydration, physical exercise can create more heat than the body can disperse.

I think the record here is 122 officially. On the asphalt it's considerably hotter.