Originally Posted by Fox hunt
Why is the highlander rated for towing more pounds then the new 4Runner? the 4Runner seems like a very sturdy vehicle.
I'm sure the 4Runner - which is based on the Landcruiser Prado chassis - is sturdy, but structural strength is only one of many factors in towing ability.
If trying to guess towing capacity, I would look at factors such as wheelbase and rear overhang for stability, transmission cooling and durability, engine power and cooling, vehicle weight, and rear suspension and tire capacity. Although they are coincidentally identical in wheelbase and width, and the 4Runner would be expected to be superior in some other factors, the critical limiting factor (whatever it is) may favour the Highlander. Weight may be a bit of an issue, since the body-on-separate-frame construction of the 4Runner makes it hard to keep weight down and some 4Runner variants are a bit heavier than a Highlander, taking drivetrain capacity instead of leaving it for trailer weight. There is little difference in engines (slightly different sizes of the same engine family).
Toyota isn't guessing - they test their vehicles' towing performance against the SAE J2807 standard, which is based on the performance of the vehicle while towing a trailer in various conditions. The vehicle must pull and stop and control the trailer, while meeting performance targets (such as time to accelerate, and speed maintained up a grade) and not overheating or otherwise failing.
SAE J2807 specifies a reasonable hitch weight of 10% of the trailer weight (rather than the huge loads some people favour), so the ability to withstand high load downward on the hitch may not be a big factor.
Finally, although the ratings of the two vehicles are different, they are very close.