Originally Posted by
achoo
1. If your body is dumping 500+W of heat because you're putting out an average of 200W while riding, that 134kJ will be moot in a bit over 4 minutes. Just like I said earlier, it'll make you feel better for a while, but it won't make much difference.
2. Good luck keeping your water at 5C while riding in 35C temperatures.
3. Good luck drinking a full liter of water fast enough for the mass of water to have an appreciable effect on your core temperature.
The cast majority of your cooling is convection & evaporation, I agree. What cold water helps with is adjusting the balance. Given that you body temperature is basically fixed, the small 1-2 deg F rise in body temperature makes virtually no difference to your cooling rates. This is especially true once you've achieved saturation with sweat. Sweating more doesn't help.
Let's say, you're dumping 500W of heat, but only able to cool 450 W. That 134 kJ is enough to keep you balanced for 45 min of riding. You don't need to drink it all at once, the important thing is that it does have meaningful effect on keeping your core temperature down.