As mentioned in another thread, I have a GX460, which is full-time AWD. For directional tires, which can't easily be part of a five-tire rotation, what do people do for spares, and how far and fast can you go without damaging the transfer case or other components? Around town would be one thing, but on cross-country trips of close to a thousand miles in a day, the inability to finish the trip makes a directional spare unappealing.
Yes, I have read the manual. It is not helpful - it says "Do not mix tires of different makes, models or tread patterns. Also, do not mix tires of remarkably different treadwear." It also indicates a non-crossing rotation, with the spare included on the passenger side (and the dealer has never done so to my knowledge). Even following that, the spare (and the passenger side tires in general) will perforce have lower treadwear than the driver's side tires. What's "remarkably" different, and can a long road trip be finished? What if it's a driver's side flat and the spare is pointing the wrong way?
The original question remains - what do people do for spares in this situation? Is it simply not worth running directional tires on AWD?
Don't take this the wrong way, but your GX460 (and the previous gen GX470) are basically 4runners (in fancy clothes). Many of the mechanical parts are interchangeable between the two.
First, good on reading your owner's manual...people who do that seem to be rare.
Second, I would post your question and concerns on forums that deal with 4runners/GX470/460. The popular t4r.org has a section just for the Lexus GX470/460. There would be people there more familiar with your vehicle specifics.
Third, your vehicle (if it is similar to my '05 4runner) should be 'full time 4WD'...at least that's what people on the Toyota side call it since you have a transfer case that can be placed in 4Lo and locked. AWD vehicles like Subaru's don't have that option.
And if like my '05 4Runner, you would have an open differential in the front, back and center with electronic stability and traction control. This means that as long as you don't lock the center diff, the wheel between front and rear can turn at different speeds and wheel between left and right can turn at different speeds without any mechanical binding.
Ideally, you'll want to run tires with that are the same type (all season, all terrain, etc.), same tread depth and same model on all 4 corners...and you want to keep the tires at the same tread depth by proper tire rotations.
As for the spare...I wouldn't worry too much about it. In the owner's manual it states that treadwear (tread depth) shouldn't be too different. How different? Well, ask ten different people and get ten different answers. In my opinion, as long as the tread isn't worn out on the spare or the running tires, you shouldn't have any problems....at least mechanically. Now, the electronics may throw a code or two because if the rotational speed of one wheel is different (cause by a significantly higher/lower tread depth) from the others, it might 'confuse' the electronics.
But you might be able to compensate with adjusting air pressures or by simple turning the electronic 'nannies' off...if you have that option.