An exmark dealer told me once between a 1/4" and 1/2" of tread left is a good time to change the tires. Someone told me he said that because he wanted to sell me tires, but he knew I had someone else I got my tires from, plus I think he would have told me to change them a little sooner if he thought he was getting my sale. Make sure you don't do a lot of (unnecessary) turning on asphalt or concrete because thats what eats them up. Hope that helped!<p>----------<br>"guido"<br>David M. Famiglietti