In the P2 hybrid (Hyundai's scheme), the motor/generator starts the engine and matches it's rpm to the transmission input shaft, then closes the clutch to connect the engine to the traction motor/transmission input shaft. So the syncing electronics are keying directly off the transmission input shaft rpm not the wheel rpm. I've been driving my hybrid Tucson since late April, and I have not fully grokked the EV mode algorithm, but from my observations the algorithm will shut down the engine and run off battery power when the SOC is 75% and run in EV mode till the SOC is 45%. This is at all speeds--even on the freeway and even going uphill on the freeway. There are exceptions: the car will stay in EV mode if you are moving very slowly and light with the throttle even if the SOC is below 45% and the engine will start and chip in, of course, if you're accelerating hard no matter a full SOC. The point is: I don't think moderate changes in tire inflation matters one whig to the EV mode algorithm. It's going off SOC and power demand from the driver mostly. Temperature figures into the scheme too.