These days, there's a lot more than horsepower that goes into tow-ratings, especially in the 8,000lb and over range!

While you need to have sufficient horsepower and cooling, chassis strength and braking capabilities are also critical.

We had a Jeep Grand Cherokee SRT-8 with 420hp & 420 ft-lbs, but it was only rated to tow something like 3500lbs, even when lesser-powered Grand Cherokees were rated at 5000 or 6000 lbs. Turns out the SRT-8 had a different transmission and the park pin in that transmission wasn't throught to be strong enough to hold a fully loaded Grand Cherokee and a maxed-out trailer on one of San Francisco's steepest hills.

Liability insurance for the car company, warranty claims, and even the marketing department determine tow ratings as much as the horse under the hood.