Over-the-air (OTA) multiprobe setups provide an efficient way to characterize the performance of today's advanced wireless communication systems. In this paper, the measurement uncertainty of such a setup using a car as a test object is characterized through three experiments: measurement system analysis, channel sounder measurements, and probe coupling measurements. Four issues were in focus for the analysis: precision, realization of the wireless communication channel, coupling between the probes, and the influence of the test object size. The analysis shows that a large test object such as a car in an OTA multiprobe ring will affect the measurement uncertainty, but only to a small degree. The measurement uncertainty expressed as expanded uncertainty was below +/-1 dB, which is a level that would not violate best practice total uncertainty levels for comparable OTA methods.