Do NOT change only the front tires!!! There are a ton of threads on tourqe bind that is caused by not changing all the tires at the same time. The problem is with an awd drivetrain it is very sensitive to unequal tire tread heights. That being said however, some people will say it ok to do this IF the back tire treads are about the same as the new tread. If it were me I'd rather change all 4 tires than risk tourqe bind problems because any money you save on tires would be lost on fixing tourqe bind