The popularity of the autonomous driving requires to establish a data communication path among vehicles. Due to its low price and easy deployment, the WiFi device is a possible approach. Motivated by this, in this paper, we study the performance of IEEE 802.11a for vehicle-to-vehicle communication. We especially focus on the impact of multi-path and Doppler spreading to the time synchronization, which is the main challenges in the vehicle-to-vehicle communication due to the high mobility. We also propose the possible approach to improve the time synchronization performance in the IEEE 802.11a by optimizing the preamble design. We evaluate the average synchronization error of our proposed methods through simulation. Simulation result shows that replacing the preamble with the Zadoff-Chu sequence can obtain the best time synchronization performance.