I've ridden from 8deg with 20mph added windchill to 101deg with 90-some% humidity. I much prefer cold to heat,it's easy to dress warm. In the summer I pick a route with as much shade as possible,drink planty of liquids,and wear cooling head and neck wraps. Can't remember the name off the top of my head,but this one company makes wraps filled with gel pellets that absorb water. It's like having a wet washcloth on your head/neck,only it doesn't drip and it lasts for hours.