My wife's 2007 AWD Sienna has one front tire in pretty good condition and one that is nearly bald. The rear tires are maybe 75% gone.
I took it into a tire store to replace the nearly bald tire and they refused to do it. They say Toyota says that you have to replace all 4 tires at the same time or it will damage the transmission on AWD cars.
I pointed out that his store has replaced one tire on three occasions on this very Sienna, and the dealer has replaced one tire twice. (The tires seem to attract nails like they have magnets in them...) All without damaging the transmission. Additionally, I have had two AWD cars for the past 15 years, have never replaced all 4 tires, without damaging the transmission. He still refused.
I pointed out that the pretty good front tire will be closer in diameter to the new tire than it was to the nearly bald tire; yet the nearly bald tire didn't damage the transmission. That made sense to him and he agreed to put a new tire on.
Now for the question...
Is there any truth to this? Does Toyota really require replacing all 4 tires when one needs to be replaced, or is he just making that up? If true, we would have had to replace 20 tires when picking up our 5 nails. It also implies that putting a spare on will damage your transmission, as it certainly won't be the same as the other three tires.