Scalable Service-Oriented Middleware on IP (SOME/IP) is a proposal aimed at providing service-oriented communication in vehicles. SOME/IP nodes are able to dynamically discover and subscribe to available services through the SOME/IP Service Discovery protocol (SOME/IP SD). In this context, a key performance criterion to achieve the required responsiveness is the subscription latency that is the time it takes for a client to subscribe to a service. In this paper we provide a recap of SOME/SD and list a number of assumptions based on what we can foresee about the use of SOME/IP in the automotive domain. Then, we identify the factors having an effect on the subscription latency, and, by sensitivity analysis, quantify their importance regarding the worst-case service subscription latency. The analysis and experiments in this study provide practical insights into how to best configure SOME/IP SD protocol.