The pilot and his pilot-rated-passenger were conducting a local flight in the tailwheel-equipped experimental airplane. The accident occurred during the first landing after the original main landing gear, equipped with bungie-cord shock absorber, had been replaced with a main landing gear equipped with a steel-spring shock absorber. The pilot reported that after a normal touchdown on the main landing gear he pushed the control stick slightly forward to keep the airplane from ballooning, but the airplane nosed over during the landing roll. A witness reported seeing the airplane’s tail continue to rise during the landing roll until the airplane nosed over on the runway. A postaccident fire destroyed the airplane’s cabin and the inboard halves of both wings. A postaccident review of the airplane’s weight-and-balance record indicated that the owner/builder had correctly recalculated the center-of-gravity (CG) position after the main landing gear replacement, and although the CG location had not moved appreciably, the wheel axle position had moved aft about 2.75 inches, thus increasing the airplane’s tendency to nose over during ground operations.