Originally Posted by RVDude
My reference was specific Lexus (a "full time" AWD system) where the vehicle manufacturer tire spec will not allow a difference of more than 1/16 inch in tread depth between tires.
You might want to check to see if this Lexus utilizes a direct (pressure sensing) or indirect (ABS input related to tire diameter) low tire pressure warning system. Toyota has used both, and false tire pressure warnings have been reported with the latter system when the spare (with no wear) is put on the ground with the other tires.
A center differential (required with a full-time AWD system) allows relative differences in front and rear wheel speed. That's why it's there - even with the same size tires, the front and rear wheel speeds will vary in every turn since the front and rear tires don't follow the same path.
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