messed up my old post but

Tires are designed to flex in certain areas of the shoulder, when you pinch or stretch a tire on a wheel that is too narrow or too wide, you force the tire to flex where it is not deigned to do so. This makes the tire generate and hold more heat (a tires worst enemy) which breaks the tire down faster resulting in shorter life and higher chance of failure. Also, every major brand tire is covered by the manufacturer's warranty for workmanship and manufacture defect. This warranty is void if the tire is mounted on a wheel outside the tire manufacturer’s recommendations.