After departure from an uncontrolled airport, the pilot was advised by personnel at the airport that they saw the left main wheel and tire fall off the airplane. The pilot decided to continue to the accident airport. After flying around to decrease the amount of fuel on the airplane, he landed using runway 30. The airplane pulled to the right until it departed the right side of the runway and tipped onto its nose. The airplane sustained substantial damage to the right wing spar. The pilot reported that he examined the main wheel bearings 2 days prior to the accident for the correct spindle nut tension. He believes that the left wheel spindle nut cotter pin was inadvertently omitted or not installed correctly during the wheel reinstallation on the airplane. He said that a more thorough inspection of the wheel bearing service work should have been performed, and that a more thorough pre-flight inspection could have caught the problem.