First, I want to give a big shout-out to my friend Robin Blackburn who will be putting 9 months of training to good use this weekend competing in the IM Kentucky. For all of us who Father Time has robbed of that ability, get some for us too Robin!
Second, I wanted to give an update on my tire experiments after a few hundred miles. I have settled on Michelin again, because the sidewalls are just so much more robust than Conti tires, even the Gatorskin. I am now running my standard, long time favorite Pro3 Race 23mm tires in front, and Michelin Pro Optimum 25mm in the rear after skidding through 2 Pro3 Races in back in 6 weeks after single 10-15 ft skids.
The Pro Optimum don't roll quite as well as the Pro3 Race, but I can't notice any difference in wind drag. I'm not sure the Optimum roll any slower than a Pro3 25mm would either. What I get in return is a tougher tire (I did have a thorn flat, but the thorn forests go on for a thousand yards in places these days, and those dry thorns are hella hard) that is very hard to skid, AND stays hooked up extremely well in turns.
We have a lot of sharp hairpin turns along the SE side of Lake Natomas, and I am starting to trust the Pro Optimum tire now to stay hooked up even over light sand and gravel. The result is less braking and faster overall lap times. The ride is also better over large road cracks and medium stones, and pinch flats less likely. They also don't leak down as fast, having more internal volume than 23mm tires do.
The Gatorskin AKA Ultra Gatorskin tire isn't as bad as my 1st impression, because once the rather extensive pips wore off the crown the tire settled down a lot and stopped hopping all over the trail and looking for reasons to break loose in turns. It might have more puncture resistance than the Pro Optimum too, but the sidewalls are just too fragile to be safe when riding long distances. I don't want to spend 2-3 hours riding home praying some make-shift boot is going to hold. The Optimum's ride is much less harsh, and much more skid resistant.
The Pro3 Optimum tires are a dedicated front and back tire set, which Michelin claims will wear about the same number of miles. I've been so happy with the rear tire, I am tempted to try the front tire too now. At 25mm It might push more wind, a big consideration up front (irrelevant in back), but I am thinking it will likely have a softer ride, and I am on the cusp of being able to ride 100% of the time on the hoods now, after going to carbon bars, and getting the seat dialed in.
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I had an epiphany when looking for some detail on carbohydrate, and then water digestion. It's pretty clear that your body can absorb a maxed out carb-water mixture, like Gatorade's 6% solution, faster than it can digest the carbs in this mixture on hot days. This is because both the large intestine, and the small intestine can digest water, but only the small intestine is capable of digesting carbs.
No matter what the source of carbs, when the mix of carbs and water in the small intestine exceeds some threshold level, the mix, carbs and all, is swept into your large intestine where the remainder of the water is absorbed very efficiently. Unfortunately, the undigested carbs can no longer be digested by you, but are instead fermented by bacteria in your large intestine (colon). The required intestinal micro-structure, nor amylase to break down carbs, are anywhere to be found in your colon. The bacteria's fermentation creates the gas and bloating we all know and hate.
Even with your entire GI track working at max capacity, your ability to sweat still exceeds your digestion rate. If this disparity persists, your body will take water from inter-cellular, intra-cellular, and finally, blood, to make up the difference.
As your body pulls water out of your blood, reducing blood volume, it puts a tremendous strain on your heart and cardio system to maintain adequate blood pressure. At some point near death, your body will attempt prevent unconsciousness by closing off your capillaries to maintain blood pressure, causing your skin to go dry and your core temps to soar. This condition is known as heat stroke.
To prevent internal organ damage, and even death, you must cool the body in a way that does NOT depend on sweating. Immersion in water, and ingesting cold water is about as good as it gets. Having someone hose you down until your body temp is below 100F is great, pouring water down your back and over your head good, and/or a sock full of ice around your neck and between your legs a potential life saver. Rehydrate as rapidly as possible by ingesting huge quantities of sodium and water. It's impossible for you to absorb water without sodium. Manage accordingly.
Nunn and water, especially distilled water, is an excellent electrolyte protocol. Distilled water, having zero osmotic pressure, will support the maximum rate of sodium and water digestion - the sodium absorption required to maintain an isotonic electrolyte balance as new water is absorbed into the bloodstream.
Therefore, the limitation on athletic performance on hot days is neither muscle endurance, VO2max, forestalling glycogen depletion, nor even electrolyte management, but your ability to digest water fast enough to keep up with requirements for sweating sufficient to keep your core body temps under control while avoiding dehydration.
All of this is again raising the question in my mind as to whether synthetic fibers, which transport, but do not absorb water, are a major contributor to dehydration on hot days. Cotton and/or linen blends may well manage available digested water more effectively.
This speculation is informed by many studies that show that while men sweat more than women, women are less susceptible to dehydration and heat stroke on endurance events precisely because they sweat less.
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