I personally think there needs to be some agreement as to what penalty / guidelines if any will be imposed for changing a tire. Because someone will hit a wall and badly warp or fail a wheel. A team should be able to recover from such an incident and still compete for the win. I think a 10 lap penalty for each tire changed would be sufficently painful to stop teams from taking advantage of a fresh set of tires half way thru the race. In addition a team should be allowed to only change a single tire per pitstop. Multiple tire changes during a stop would be an additional 20 lap penalty.