To rotate tires I need to jack up my wrx front and rear. But since the car came with one jack, I have to use a generic jack.
The subaru jack has a lip where a metal strip under the car fits into. If I use a generic jack which doesn't have this lip, it would crush the metal strip.
How do you do it?
Just put the jack on the suspension arm close to the tire. You're also going to need at least one jack stand.
The car jack included with the car should ONLY be used in emergencies to replace one flat tire (at a time - and since you only have 1 spare then more than 1 flat means you're stranded or have to call for a tow). The included car jack should NEVER be used for maintenance on the vehicle. For that you buy your own shop-quality jack and stands (and optionally car ramps but I don't trust those). You jack up the car at one end to put a stand under 1 or 2 sides near that end and then jack up the car at the other end to put 1 or 2 stands at that end. Make sure you get solid stands since you may be using them to work under the car.
For what you describe, you should NOT be using the included car jack at any side or end of the car. That's just to lift the car to do an emergency tire swap. It does NOT have a wide enough base to provide a stable support. Look at stands to see how much wider is their stance and they use a tripod layout for stability rather than a small solid square base of the included car jack.
If you intend to perform maintenance on your own car then get the right tools for the work. If you are unwilling or financially strapped and cannot afford the right tools, let a car shop do the work. Doesn't the dealer that sold you the tires do tire rotations for free? If they are the original tires (came with the car when you bought it) and the car dealer won't do free rotations then ask around the local car shops to see if they'll do it for free, or free when you have them do an oil change (or any work that requires hoisting the car), or find a coupon in a local flyer from a shop that does free rotations (as a lure to get you to know them and perhaps get other work done there then or later).
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