When using the signal from the Global Positioning System (GPS) for precise estimation of a vehicle’s heading, the main challenge is finding the integer ambiguities in the carrier phase measurements. If the distance between the receiver’s antennas, also known as baseline length, is used in the process of solving that challenge, the resulting solution’s stability and precision can be enhanced, particularly for single-frequency L1 receivers. This paper presents a study of the overall influence of this baseline length in the precision and accuracy of the heading estimation, using raw measurements from two GPS single-frequency L1 receivers. Conclusions are presented based on the results from field trials for baselines up to 8 m.