I was out for 40 miles Wednesday in the heat of Illinois and did ok. My pace was a little better than average given I ran 4 miles before the bike ride. I manage to average 19mph in the basic flats of Illinois. I went through 2 bottles of water in 90 minutes and then on empty the last 30 minutes or so could have used more. I find the heat ok seems like it is worse but the stats do not say it is.