Hutchinson Python tires improved the speed of my mountain bike, however since I do 95% of my riding on pavement I decided to buy a Kona PhD last year. Neither bike is as fast as my road bike but the riding position relieves discomfort on my bad back over longer rides. With the Kona I average 2 MPH faster than my MB expending far less effort so over the course of a 50+ mile ride the difference is very apparent. No supension components on a lighter weight bike with skinny tires makes a significant difference.