I just switched from Continental Ultra Race 700x23 to Continental Grand Prix Four Season 700x25 on my carbon road bike. The Ultra Race's had lost several patches of tread, about 1/16", after about 1,500 miles. The Grand Prix's weigh the same but seem much tougher. The Ultra Race's have a more supple feel. I went to the larger size for riding short stints on gravel. I only have a few hundred miles on the Grand Prix's but they look like they will last much longer. They were not cheap. I paid about $45 each on sale.