The Cat 4, 3 and P/1/2 Georgia Games road races will start between 10:30 and 10:50. With 57, 76 and 96 mile distances we'll be riding through the hottest part of the day. The forecast is for a mostly sunny high of 95 degrees and 55% humidity. So, what does that mean?
A RACE OF ATTRITION
The high heat and humidity will make these races (especially the Cats P/1/2 and 3) races of attrition. Racers who are sensitive to weather extremes will wilt. Much of the peloton will get worn down simply by the sun beating water and nutrition out of their bodies.
I personally enjoy these sorts of conditions for racing. The harder the better. It's the same thing as racing in the rain - many racers will be on the back foot simply because of conditions. And I see it as, for me, just another small factor in the race.
That said, I always want to make sure to be prepared for the heat. Once dehydration hits, you're screwed. I don't know of any way to rehydrate quickly in racing conditions; and no matter how well you hydrate, you're pretty much sure to end the race dehydrated. Your body simply cannot absorb enough water per hour to replace the water it loses.
HOW MUCH SHOULD RACERS DRINK DURING A RACE?
The maximum amount of water your body can absorb in an hour is about 1 liter. We're talking ideal situation - body at rest, etc. The realistic number your body can absorb in racing conditions is closer to .5 liters. So, your body can only absorb about a bottle an hour, and your body is losing more than a bottle worth of water an hour.
So the simple method would be figure out how many hours you're racing for, and bring that many bottles. But that doesn't work for most racers.
For many racers (and people), having a dry mouth is a psychological weight that is hard to shake. If you have a dry mouth, that doesn't necessarily mean you are dehydrated. If you race for many hours, you will get dehydrated no matter what you do - even if you drink more water than you can absorb just to keep your mouth wet. If you cannot get over your dry mouth, then keeping your mouth wet by drinking extra water would be worth it for the mental gains it gives you.
A huge factor is that everyone absorbs water at different rates, so some racers can absorb more water per hour and so should drink more. This gives them a great advantage in racing under these sorts of conditions. Also, it possible that your body will absorb water at different rates as different points in the race because of the effort you're exerting, so having extra water increases the likelyhood of absorbing the absolute maximum your body is capable of at any given time.
SPORTS DRINK vs WATER AND GEL/BAR/ETC
I think this is personal preference, as well as what you're accustomed to training with. I dislike the sticky mouth feeling I get from sports drinks, so always opt for water and a bar. Regardless, because your body is losing other substances with your sweat (minerals, etc.), it's important to take on nutrition of some sort while hydrating. Just make sure whatever it is holds up after being in 100+ temperatures for hours.
I believe you can use heat acclimatization to hold up better during hot races. The way I do it is lunch rides. In the middle of the day I'll do a 1.5 hour ride without any fluids the entire time. When it's really hot, I'm pretty dehydrated by the end. The advantage, I believe, is mental more than creating a physical adaption. It helps to know exactly what your limits are, when you are reaching them, and also gives you the confidence that you can ride hard for a period of time without taking in additional fluids.
I have a few other tricks I like to use when racing in the heat:
1. Bottle of water in my belly. Basically, I drink a bottle on the line while waiting for the race to start. So instead of having that bottle in my jersey pocket, I have it in my stomach. And if I'm not thirsty, no big deal, I just toss it on the side anyway. Too often I've seen racers on the start line waiting for a race to begin have to go back and get another bottle having drained one.
2. Close your mouth. Sometimes I find my mouth open when riding at paces when I really could just breathe through my nose. When the dry heat from the road is blasting up, it along with the wind really dries the fluids out of your mouth. Never waste that precious fluid that your body already has. By the end of a long race that could be 8oz (totally making that number up) of water your body doesn't have to absorb.
3. Stay calm. The more you worry about being dehydrated, the worse it will be. Try and stay calm, race like you normally would, and know that everyone else is in the same boat as you.
4. Drink regularly. If you drink a bunch at a time it will be harder for your body to absorb, and it will also be more likely that you "miss" a moment to drink. Drink as continuously as realistic.
SO, WHAT'S THE PLAN?
My race will be 76 miles, so I anticipate a 3-3.5 hour race. My plan is to have 2 insulated bottles on the bike, one in my jersey pocket, and to drink one on the line. If I hydrate properly leading up to the race, I believe that should be enough for me, especially because I'm pretty comfortable riding in mid day heat at this point. For food I'm thinking to do baby food pouches, because they are nutritious and wet (ie a dry bar needs water in order to be absorbed, which isn't ideal). That said, they are usually relatively calorically low, so I'm not for sure on that yet.
Regardless of how you plan to race your summer races, do what works best for you and be safe! Dehydration is no joke.