Great day to get out for a ride. Weather was a bit cold on the way out, but I was warmed up after the first 10 minutes. I wore 1 base layer, arms, knees. Winds were favorable. I did modest tempo on the downhill. When I reached the bottom of the descent, I noticed that my front tire had gone soft. I've no clue why. I ended up stopping at the Caesar Chavez entrance (a safe place to stop), and changed inner tubes. I thoroughly inspected the inside of the rim and the inside of the tire. No signs of debris. So I proceeded to install the new inner-tube and inflated it. It took 2 CO2 cartridges to fully inflate it. The tire held up for the remainder of the ride, so I'll see what happens in the next few hours. This is the second flat in 2 rides. Very odd. I was able to verify that the first flat had a hole. I put it in a bucket of water and sure enough, there was a puncture. but it was a single puncture and not a snakebite. I'll have to look at today's puncture to see if there is a similarity. That set aside, I felt pretty good today. My legs were fresh and I was able to hold good tempo for the better part of the ascent. I was pushing the pace a bit, in anticipation that the front tire would go flat. I didn't want to have to call for help. Other ailments were intermittent cramping in my right calf, but it lasted only a few seconds. Concentration was good, but a mixed bag. Some of which were urgency given the nature of the mishap, and otherwise good focus. No panicking. Other than the puncture, the gear worked great. I put the gopro into the highest quality setting (I forget what it's called). Will have to see what the quality is like on my iPad.