I drive a 2013 AWD L. I checked the owners manual for the answer but the wording was non-specific. The manual said “do not to mix tires of remarkably different tread wear”(p775).
Three of my tires are Michelin Primacy MXM4 98W with 8/32nds tread left. Thanks to a pothole I am also running a Michelin Energy S8 MXV4 98V. The Energy tire is the original spare and has never been used and the specs list the new tread as 9/32, although I measure it closer to 9.5/32nds. Is 1.5/32nds considered remarkably different or is it within Lexus specs?

I do plan to replace all four tires because of age but do I need to rush to do this because of tread depth differences. AAA recommends replacing tires that are 5 years old and NHTSA provides a 6-10 year range. The Primacy’s are 4 years old.

I was also thinking about replacing all 5 TPMS sensors when I replace the tires given the cars age and the likelihood my next tires will be on the car for 5 years. I have no TPMS issues, but given how long I keep tires this might make sense.

 

The reason, you do not want to mix different tires, is the impact on AWD. If you have different wheel sizes or tires wearing at a different rate, it might damage AWD system designed to operate with same wheel size.

 

Its an old wives tail - that's what differentials are for. If you put a new spare on the rear of an RWD, the left rear and right rear are going to be a little different but nobody has a conniption about that. Its the same with AWD. The tire dealers just want to sell you 4 tires and the car manufacturers are just looking for any excuse to deny a warranty claim.

 

I’m assuming the full size spare is 8 plus years old and is in more need of replacement than your 4 year old tires. I would look for a used tire exact to the tire you are replacing. At 8/32nds you could also do one new tire but exactly the same model as the others. Keep in mind that mixing tires is not an old wives tale. Each model tire has different tread patterns and possibly different rubber compounds. These all determine the tires traction and mixing these tires across an axle can be dangerous. Example I mixed the 2 front tires on a Camry and going 65mph traffic came to a sudden stop. I stomped on the brake pedal and the steering wheel pulled to the right and I went into a slight skid and barely missed the car in front of me. Yea your abs will kick in to help avoid wheel lock up but it was already too late.
The Primacy MXM’s are designed to handle better while the Energy is a bit more comfortable and giving.

 

Old wife's tale? I've totaled my last LS due to mismatched+old tires. Never mix and match. Never drive on tires older than 4 years. Prone to bulges and internal damage.

 

If it were me, I would drive with the odd tire, but I don't drive my LS aggressively and I'm always local with it. I still have my original spare from 2007. If I ever had to put that on, I'd be changing it immediately.

As to your TPMS, my original ones are still going strong. I remember in April, 2019, when I got new tires I was thinking of changing them but didn't and they're still reading out just fine. My 2008 612 have the original TPMS and they read out both pressure and temperature. Of course your results may vary.