I ride a Surly Pugsley to work everyday and Ive noticed that my pace has been getting slower over the past few weeks especially. Ive also noticed that my rear tire is getting really worn down and will need replaced soon. Could this cause my pace to slow or am I just getting slower in my old age? I was hoping that the tire would last for another couple months, but Im putting more miles on it than I thought. I average about 120 miles a week on it, so I dont think its conditioning.