Double-check so the wear multiplier is the same. If wear is drastically different that's probably the case. If the change is fairly minor it could just be a difference in the amount of rubber on the track. With less rubber on track, you will slide more and put more energy into the tyres, leading to more wear.
the rubber on the track and the wear multiplier are the same. Still, about 2% more tires are consumed per lap in a race. Can't some graphics settings affect this?
No. Is it offline or online? If it's offline, configure the same initial rubber in every sesion and put in static and check again. It would be good to compare the telemetry and replays to be sure that the driving style is the same in both sessions.
Online is more difficult to control it. You can ask for the configuration and the rubber files of every session of the server. Why you can't do telemetry? You can install the DAMPlugin.
