Picking the right tire is one of the easiest ways to gain speed on the bike. Of course, actually training is a much bigger piece of the "go fast" puzzle. Skipping the hard work and just buying a fast tire isn't going to get you a win on race day, but tire choice can make a difference in your results when all else is equal. The difference between a set of fast tires and a set of slow training tires could result in a rider having to put down over 30 additional watts of power to keep up. (check out Tom A.'s chart here) For those of you training with a power meter, you know that 30 watts at threshold power is like the difference between you at your peak of the season and you at the slowest part of your off season.
The problem is, the fastest tires are often the thinnest and offer the least amount of flat protection. The slowest tires are the thickest, and offer the most flat protection. We need a tire that balances speed and protection to meet both of our needs.
For years (up until about 6 months ago) I did all my training and racing on one model of tires. The Continental GP4000S. It's a quick tire, but offers pretty good flat protection. The chili compound they use grips really well in the wet and dry conditions. Compared the the Michelin ProRace tires I used before, these would get way less cuts along the center. I would get about 5000 miles out of an average set. When I bought a new set, they would go onto my race wheels (for the years I actually owned race wheels) and I'd take the old tires off my race wheels and cycle them to my training wheels. It was a system that worked pretty well. I always had fast tires, and very rarely had flats. I only had to buy about 2 sets per year. As an all around tire, it worked very well. It seemed like in the last 2 years the sidewalls got a little more thin. I was dealing with more frequent cuts to the sidewalls than usual. It seemed to happen before the GP4000SII came out, but the GP4000SII had the same issues. Even still, I have no problems recommending these as an all-around tire, or as a tire for half ironman or ironman events. Long triathlons like that require a tire that is fast, aero, and durable. The GP4000S (and SII) has all of that.
In the past 6 months, I decided I wanted a longer lasting set of tires with stronger sidewalls for training, and a set of faster tires to race on.
For my training tires, I went with the Bontrager AW3 Hard Case (pictured below). They offer a "Hard Case" and a "Hard Case Lite" model. The "lite" model has a puncture belt around the center of the tire. The "Hard Case" model has the belt around the center AND around the sidewalls. They have a lower model AW2 which costs less, but you get less TPI. Typically, the higher the TPI of a tire, the more supple it is. The more supple a tire is, the better it rolls, the better it grips, and the better it feels on the road. The AW3s weigh more than my GP4000s, but I was pleasantly surprised by how they felt on the road. They don't feel like a training tire. Other training tires I've used felt like I was rolling on garden hose. You feel every imperfection in the road. Like Tom A says, life is too short to use crappy tires. These AW3 Hardcase tires are definitely not crappy tires. They still haven't had any punctures. They still don't have cuts. The sidewalls still look great. I don't worry when i ride through gravel. So far, they seem to be the perfect training tire.
They also definitely aren't race tires. I've never seen a rolling resistance test of them, but I know they aren't as fast as something like a GP4000s. For racing, I want something that rolls faster.
My "go to" tire for racing was the Vittoria Corsa Evo line of tires. For crits, I still might use them this year. It's what I have glued onto my tubies, so I'll use them until the tire goes bad or the glue goes bad, whichever happens first. My main complaint about the Vittorias is that they seem to cut and puncture easier than other tires I've tried. They also don't last for nearly as many miles as others. They are fast and grip well, but it's hard for me to trust them in long road races. In crits, where you get a free lap, sure. In a road race where you have to chase yourself back into a race after a flat, I'm willing to give up a few watts in order to remain puncture free.
For my clinchers, I'm excited that I just got some Bontrager R4 tires in 700x25. I haven't seen rolling resistance tests on the 700x25, but the 700x22 R4 Aero model tests well. It's only the equivalent of 2 watts slower than the GP4000s. Typically, a wider tire like a 700x25 tests faster than a 700x22, so I would wager that the GP4000s and the R4s are basically just as fast as one another. The R4 has the aero wings on it, so it should be a great aero fit on my wide clinchers. The R4 has the "hard case lite" technology, so it has an anti-puncture strip around the middle of the tire, similar to the GP4000s. All around, it seems like a very close tire to the GP4000SII, but I'm hoping that the sidewall is a little more tough.
My R4s literally don't have a single mile on them yet, so I can't give them my official seal of approval; however, the reviews of the tire are very good. Based on what I've experienced with my AW3s during training, I'm certain that I'll enjoy racing on the R4s. In about 6 months I should be able to report about how they held up, and let you know whether this is the replacement of the GP4000S as the perfect all-around tire.