Originally Posted by AZjeff
Why would a car with 20k miles have new front tires and garbage rear tires?
This. Something screwy is going on either with the vehicle or how we're getting this information relayed.
What is "garbage" rear tire? Please (directed at all random persons! lol) never write a colorful opinion instead of objective facts like what brand and what the problem was, for example was it worn out? I don't understand qualifying a tire as garbage instead of worn out if it was worn out, nor calling a tire garbage but replacing it with a low end brand if it wasn't worn out.
On the one hand we could pretend or assume this is a perfectly normal vehicle that has been in no accidents and normal tire wear, that just needed new rear tires. In that case no, on rear wheels especially, if it was aligned acceptably up to that point, it would be as arbitrary to align right after getting tires as it would be to wait another 20K miles and then get an alignment, or at whatever point there seems to be an alignment problem.
On the other hand something is screwy in that it has been chewing through tires this fast, and since you just got it, it may be quite difficult to contrast what it handles like now and what it should handle like with a good alignment. It wouldn't have handled right with new front and old rear tires and it won't now with different brand new rear tires, so you have no baseline for what feels right for this vehicle. At least you have same age tires on the same axle.
Finally, with (almost) new front tires and now new back tires, there is no reason to replace them "next year". If they were crap for cold winter months then now would be the tire to replace them but if they do okay for this winter you might as well run them until whichever pair wears out first, though you didn't mention make and model of vehicle nor what specific tires are on it.
PS shops that offer a free alignment check are a way for them to sell you an alignment even if you don't need one. If the front tires are not worn unevenly, I would wait until you notice any uneven wear (checking frequently), unless the oddity of having worn out and different tires by 20K mi was because this car was in an accident and frankensteined back together into a whole car at a junkyard, in which case the alignment should definitely be checked, and the trueness of the frame (meaning unibody) and everything else with a fine tooth comb, not so much the normal wear items in the suspension because those shouldn't have worn much at all by 20K mi, but certainly you should not ignore them either.