I was wondering...how do you know when it's time to get new tires? I have Bontrager race lite X tires and they do not have any tread on them. They came that way new so I do not have a bench mark that I can watch to see if the tread has worn down. Any help on this would be great. Oh by the way I have about 700 miles on them. Just wondered how long road tires usually last. Thank you!