load ratings?
 

The rear summers on my 340i will need replacing soon (they are down to 5/32nds or so). They are PSS, not the latest and greatest PS4 but they suit the car fine and the fronts have a good amount of life left (staggered).

A pair of right size tires with lots of life left have popped up locally. I guess the 255/40/18 size that is a rear for my car is a front for some kind of AMG merc. I'm very tempted to snag the pair... But here is the dilemma, at the last moment, I noticed that my tires are 99Y and these are 95Y.

I'm thinking I can get away with this by simply keeping on top of rear pressures and making sure not to overload my car. I currently run 33 front and 35 rear and generally the fronts heat up more than the rear as car is an xdrive with something like a 52/48 distribution.

Or should I be a stickler and pass until I match the load rating? Never going to see the track.

Minimal rating difference. You aren't tracking the car. You're unlikely to be loading the axle that heavily.

That said... Old PSS tires really, really, really suck. I wouldn't do it for that reason.

Bit more info... BMW specifies a whole range of tires for the f30 340i, square and staggered. Most of these are runflats with rear load ratings ranging from 91 to 95. The only non-runflat tire set was stock on my car with the track handling package with XL rated Michelin PSS.

I don't think there will be an issue. I don't plan on doing autobahn speeds with the car loaded to GVWR. (And even then the axle load is apparently supported by the other tire sets)

They should not be old, 2021 or so. I wouldn't buy older than 2020 production. My fronts are 2018 or 2019 production.

My experience with the PSS is that the compound life is ~12 months.