I was surprised to see you say the XC90 has a tow rating of 5000lbs.

That would mean a class III hitch :
http://hitches4less.com/trailer-hitch-classes.html

After some digging I verified what you said WRT tow capacity on the online owner's manual on Volvo's US website. The AWD version is rated for up to 5k lbs and the FWD version is rated up to 4000lbs.
https://www.customers.volvocars.com/owners/docs/2010/2010_XC90/2010XC90OwnersManual.pdf

You'll notice also that they decrease the recommended towing capacity pretty steadily for the AWD model, all the way down to "towing not recommended" for when you have all 7 seats full of people. In the same chart, the recommended max towing capacity for the FWD version stays at 4k lbs until you get more than 4 passengers, and then it only drops by 300lbs.

Also I noticed that on the 'tech specs' page on volvocars.com the max towing capacity is listed as 3300lbs (class II hitch) for even the AWD version.
http://www.volvocars.com/us/all-cars/volvo-xc90/details/pages/technical-spec.aspx


Meanwhile on the UK website the max towing load is listed at only 750kgs (~1600lbs).
http://www.volvocars.com/uk/all-cars/volvo-xc90/details/pages/technical-spec.aspx

According to the UK owner's manual, the max 'unbraked' weight is 750kgs, while the max tow weight is 2250kgs (5000lbs) - this time with no special chart to describe decreasing tow capacity as passengers increase.


Going back to the US specs, the S80 (same car as XC90, different body and suspension) only lists 3300lbs max tow capacity. Again, class II hitch restrictions.

If I had to make a guess I would say this rapid decrease in recommended tow capacity in the US (maybe this also exists in other markets, but I didn't see it in the UK owner's manual) has to do with the car's GVWR in the US. I don't know much about the regulations, but I suspect there's some predetermined weight assigned to passengers which has some safety margin built in - like an average of 250lbs/person or something like that. So when you get lots of people that adds up ( 7 pass * 150lbs = 1050lbs. 7 pass * 250lbs = 1750lbs!!)

The AWD version weighs more to begin with, what with all the AWD running gear and the large engine plus all the interior options they package-in in the US to force the margins up... I think they just ran out of room on the GVWR and had to recommend less tow capacity - otherwise why wouldn't the FWD version decrease at the same rate with extra passengers.

For instance, they only give 180lbs extra GVWR for the V8 AWD car over the 6cyl FWD version. When you compare to the 6cyl AWD version it's only 165lbs extra. That's not much extra margin considering they give 250lbs extra curb weight for the AWD version...

Then again maybe not - after all they /only/ give 250lbs extra curb weight on the AWD version, so that doesn't seem like enough to throw their GVWR off with 500lbs of tongue weight....

I'm stumped.

Thanks for the fun puzzle though :)

IMHO your are probably fine towing at 5000lbs for shorter distances with a class III hitch and electric trailer brakes. (DO NOT TOW MORE THAN YOUR HITCH IS RATED FOR EVER EVER EVER.)

If you were ever in an accident though, I don't think your insurance company would look favourably upon greater-than-GVWR travelling, even for short distances.

Really if you want to tow more than class II wieghts (3500lbs+) you will need a heavier vehicle with appropriate tow rating. An Explorer would probably be my choice :)

Regardless, don't forget that if you'll be towing anything for long distances you'll need an aux transmission cooler, or you'll cook your transmission. There's just no extra cooling/lubricating capacity in modern transmissions.

--
1998 V70 AWD->FWD Turbo 200k+