1. Just FYI, if you get separate rims without TPMS, no shop will mount your tires. You can get them mounted and balanced on rims and shipped to you. But the actual swap will happen in your driveway by you, not at a shop. Federal law says that a shop cannot knowingly make a working TPMS inoperable. Not a big deal for most. But perhaps a bigger deal for some. It also means that, if due to space reasons, you prefer to have a tire shop store your tires/wheels while not in use, this option isn't available to you.
2. Separate rims with separate TPMS sensors aren't really going to save you money. To program those TPMS sensors, you gotta take it to a dealer. A dealer is gonna charge you like $50-$60 to reprogram the car. Same dealer would mount new tires on your stock rims for $70ish. You'd have to do either twice a year. So you're only saving $20-$40 per year with new rims.
Considering new steel rims + sensors is gonna run you north of $400 to buy (without the tires), you can do the math of how long it would take to pay you back.
On top of that, assuming you downsize on your winter wheels, you gotta walk into the Subie dealer to have them reprogram those new wheels. They will note the non-stock size. They can't really do anything about it, now. But say a few years later you stroll in with a drivetrain issue you think is under warranty. If there's suspicion that your aftermarket wheels caused an issue, they can deny your claim. It very clearly says in the owners manual what size of wheel is recommended, and again on the door placard. They don't recommend downsizing.
All that said, there are still advantages to getting separate rims.
- Prevents winter's salt, grime, potholes, etc. from damaging your stock rims.
- Likewise, every time you mount and dismount a tire from a rim, you risk damage to both tire and rim.
- Downsizing is an improvement in snow capabilities.
- Even if you intend to have a dealer reprogram your car, you still can make the switch in the driveway on the first impending snow storm, and do the reprogramming thing when you have time. That beats being a slave to service schedules.
- Likewise, you can always switch in the driveway for upcoming warm spells, southern vacations, and the like.