I think that depends on what kind of AWD you get. On my Hyundai Santa Fe (and many other AWD vehicles, Subaru being the only exception I know of) only a minimal amount of energy is transmitted to the rear wheels most of the time.
The other thing about AWD on the Santa Fe (and many other vehicles) is it actually reduces your towing capacity. My AWD Santa Fe has a maximum tow capacity of 2200lbs; the FWD version can pull 2700lbs...
Good points, Peter, to keep in mind when considering other AWD vehicles. I was referring specifically to the Sienna, which has a centre differential and 50/50 initial torque split (all wheels truly do drive) and the same tow rating regardless of AWD versus FWD. There are many ways to do AWD, and Toyota has pretty well done them all. Subaru specializes in all-wheel-drive, and does a fine job of it, but they're far from the only ones. The British invented high-performance on-road all-wheel-drive, and Audi popularized it.
Some vehicles have higher ratings with AWD (likely due to suspension tuning differences, or better stability in low traction conditions), and for most trucks the towing capacity is just reduced by the weight
of the extra drive hardware. For the Sienna, the extra weight
would reduce the cargo you can carry, and indirectly reduce the maximum trailer weight in combination with lots of cargo, which may be a consideration for Candi.
Might be true for some vehicles, but clearly not all of them. None of the AWD vehicles we looked at in 2001 had run-flats, and the Santa Fe we bought had a full-size spare.
I was referring specifically to the Sienna. This space-for-a-spare problem is likely one reason that most minivan makers do not offer AWD, especially since they are now making the seats fold into the floor. The other vehicles with run-flats are typically sports cars with big tires
and too-small trunks (not typical towing candidates).
Candi, it sounds like you have a good handle on the run-flat tire situation. You do have the option of carrying a full-sized spare (and if you carry it all the time, using normal instead of run-flat tires), but the only good place to put it (if you don't want it on the roof rack) is in the well behind the wider side of the third row seat, which would then not be able to fold down into the floor... kind of like having some other brands of minivan