I didn't get a chance to read all the responses but I struggle badly with heat even being a 30 year native Texan. Last summer twice I pushed it to throwing up, not a fun experience. Once on a trail, once in the gas station trash on a road ride. UGH! I am considering trying a Kul Lite Vest or similar product. Have also considered for mountain biking soaking my jersey in ice water since I carry everything in Camelbak. I tend to shorten my rides if I have to but here are some other things I learned the hard way:

  • Acclimate
  • Monitor HR, mine spikes with less effort in heat so I have to keep myself at lower effort.
  • Ice in sports bra! It is heavenly and keeps core cold.
  • Ice water bath for BUFF or other headband
  • Pour water in your helmet
  • Electrolytes, I only saw you mention water. I always have Camelback on mountain bike rides but carry an electrolyte drink in cage.
  • One thing I learned doing endurance events (centuries) and racing is hydrate during the week. I rotate Gatorade and water especially weeks I know I will be putting in a hard or long effort.