I rode 150 miles yesterday to prep for a 600K next weekend. First 100 miles went fine, 11:30 am, 70-80-degrees, consuming 350 calories/hr, drinking 20oz/hour., average speed around 15mph, heart rate around 125 on the flats. Then I hit a headwind and the temp went up to 90 degrees, my feet started to hurt, I had to ride on the aerobars because my arms were weak, heart rate increased to 140 and higher. Even when I would gear down and slow the cadence I could barely get my rate to below 140. Does riding in the heat automatically increase your heart rate? When I hadn't urinated in 5 hours I knew too late that I hadn't consumed enough fluids when the temp went up (had not been a problem the first 100). With no thermometer around, how do I detect the increased fluid loss and start to compensate before it's too late? I have Shimano RT80-SPD shoes that I wore on the 200 & 300K, I moved the cleats back as far as they could go and put credit card-sized pieces of plastic over the cleats inside the shoe but still had pain between the first & second digit metatarsal/tarsal joint. Any other adjustments I should make? I have a pair of Shimano sandals, but I'm afraid the soles might not be as firm as the shoes. Thanks.