I'm with all the others that suggest future-proofing the wiring and planning for a 60amp circuit pulling 48amps continuous. It's very little more money and no more effort than putting in the thinner wires. Even if only running 30amps over it, it still works fine, even better. And it's trivial to pop in a 50amp (14-50) or 60amp (Tesla wall charger) breaker.
It's a slippery slope. First, my service is 100 amp and all my breaker slots are full. I have a quad that includes two 30s linked on the inside and two 15s on the outside. That's a 30 amp 240 volt circuit that I'm not currently using. In theory I could replace that quad with one that has 60 amp and 15 amp, but so far I can't find one. My panel is made by ITE installed in 1985 (1984 date code) and uses Siemens breakers.
If I could find a breaker it might make sense to go ahead and do a 60.
So, how about running a wire that will support a 60a service like a #4 or #6 to future proof my 30a? My understanding is that the thicker wires won't connect well to the 30a breaker as they're too big.
I'd love to upgrade my panel and service right now but got other big spending projects going on too and it's just not a good time for that.
My car is a SR so it won't benefit beyond a 40a circuit anyway right now. Yes in the future that will likely be different.
Finally, running the wire is pretty easy. The entire run is in an unfinished basement, only have to go through the wall once to get to the garage and land right where the outlet is.
If and when I upgrade my panel and service it will be easy to run another wire for a bigger circuit or maybe put a sub panel in the garage.
I've been charging on 100v 15a for three years. Just got an LFP battery put in and need to get to 100% at least once a week. And I already had a close call with an outlet on the current circuit that went bad - it only made the circuit stop working well, but could have been worse.