When I stretch a steel frame, I put my wheel on the frame, tough some times with narrow frames, and stretch it with my port-a-power. Use two thin blocks of wood between the frame and the rams, that way you won't kink the chain stays. Stretch one side a bit and then switch sides and do the other. Just go easy and work side to side until your tire fits. For some odd reason the port-a-power doesn't bend both sides equally.