I just bought a CPO 2016 RX 350 F-Sport 3 with 41,000 KM (25k Miles) on it and the dealer put brand new front tires on it. The salesguy said the original front tires did not have enough thread left for the CPO. The rear tires look pretty good, decent amount of thread left on them. Better than what I had on my first 2016 RX (was totaled). with 50,000 km. Don't know actual mileage on each tire, since many also run winter tires around here and if someone trades for a new RX they will probably keep their winter wheels.

Because my car was written off with the winter wheels and tires on it, I still have my original 20" wheels. I took them to the local tire shop and put Blizzaks on them and took the OEM tires home with me. All the regular tires are Bridgestones. I would have preferred Michelins, but you get what you get buying used...

So now I have 2 new tires, 2 66%+ tires and 4 lose tires that are 50% thread or less. How big of a problem is it to have slightly mismatched tires? I assume a car with tires that were never properly rotated would soon end up in a similar situation since the RXs are pretty strong front bias?

 

I'd check with an AWD driveline specialist as the tires have different diameters and this may affect and even ruin the AWD system. I know that you cannot put on the same axle tires/wheels of different diameter, but am not sure if the same applies when on different axles.

 

I bought a tire depth gauge this morning and the new tires are 9/32 and the other mounted tires are between 7/32 and 6/32. From what I can find online. 3/32nds should be ok, unless it is a subaru. I have been paging through the manual, but it doesn't say anything about uneven thread wear...

 

Your fine.
Your RX looks sharp.

 

Some systems may be more sensitive than others, as you mentioned on the Subaru even if using the spare (doughnut) one had to disengage the AWD