I was in the same situation a couple of years ago, I replaced the rears only with the same size tire and the fronts were 60% or so. Now after 15K miles, no problems at all.

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2022 X6///M - Toronto Red, Silverstone Full Merino Leather, Executive Package w/Remote Engine Start, Soft-close doors, Heated & Cooled Cupholders, Front Ventilated Seats, Front & Rear Heated Seats, Front Massaging Seats, Carbon Fiber Trim.

2002 X5 3.0i, Sport Premium, Titanium Silver, Grey Dakota, Cold Weather Pkg, Xenons, DICE, LED Tails, just a winter vehicle...

2007 550i, Sport Premium, Silver Grey Metallic, Grey Dakota, Nav, Cold Weather Pkg, Comfort Access, HD Radio, Xenons.