The blue and red BMWs led our convoy. At 11,007 pounds, they were the heaviest pair by nearly 733 pounds. Their bulk immediately became clear when we needed hasty acceleration to achieve cruising speeds. The X5 M's six-speed automatic gearbox struggled to hold gears and deal with the added load on minor grades. We frequently had to count on manual shift mode to get the ideal amount of consistent thrust.
The BMWs' rear air springs did wonders in leveling the load and compensating for the tongue weight. Although they lacked as many clamping pistons (four up front, one out back) as the Jeep and Porsche (six front, four back), the giant 15.6/15.2-inch front/rear brakes revealed no signs of stress throughout the towing experiment. "Good luck with trying to monitor how it's doing when towing a trailer in the Bimmer," Kong said. "There are no special menus or screens or dedicated tow mode."
On the other hand, the Jeep's antiquated five-speed coped well with the load, but the SRT8 nevertheless felt as if was lugging an overweight elephant. Interestingly, the Chrysler/Fiat rig was the lightest at 9949 pounds. Hooking a trailer to the Jeep couldn't have been simpler. With the optional Class IV tow package installed, it arrived with both four- and seven-pin connections. There was also a dedicated tow setting -- the only one in the group.
Neither the Jeep nor the BMW felt as comfortable with an extended tail as the Porsche. Though its eight-speed gearbox had trouble getting used to the added resistance and was at times confused, with 516 lb-ft of torque available at 2250 rpm, it was quick to hunker down and pull ahead. At the same time, the silent air-filled dampers modulated weight transfer and produced a compliant ride.
The Germans further showed how well their force-fed legs could pull in our two instrumented 45-65-mph acceleration runs with a 4726-pound trailer attached. The speed range represents a common street-to-highway transition. (The Jeep's 5000-pound maximum towing capacity determined our standardized trailer weight.)
The first run began at a standstill and lasted until the 65 mph hash. The time it took to get to 65 mph from 45 mph was our recorded number. The second began as a rolling start. Again, the time it took to get up to speed was the result. Both runs served as key evaluators of a vehicle's throttle, shift, and acceleration responses while under load.
The better-geared, torque-strong Porsche Cayenne dominated the first category with a 4.4-second time. Having eight cogs allowed it to get up to speed more efficiently than the lot. Next came the BMW at 5.0 seconds, then the power-deficient Jeep at 6.4 seconds.
On the subsequent run, things got more interesting. The Porsche's time dropped to 5.3 seconds, which the BMW easily matched with its responsive turbos at full spool. The 4.8-liter's considerable turbo lag elongated the Porsche's time. The Jeep continued to bring up the rear with a 6.6-second attempt.
Round 3: Track Blast
First, I must divulge our usual instrumented findings, where the BMW shined. To 60 mph from a stop, the clock spun for only 4.1 seconds. A quarter mile got decimated in 12.7 seconds at a terminal speed of 110.1 mph. Braking from 60 mph took just 112 feet. Line this X5 next to an Audi RS5 (4.3 seconds), Shelby GT500 (4.2 seconds), or Aston Martin DBS (4.2 seconds), and it will win the sprint to 60 mph every time. The Jeep is just as impressive, recording 4.6 seconds; 13.3 seconds at 103.2 mph; and an astounding 106 feet in the braking category. Porsche's largest Turbo secured itself a mid-pack position with 4.3 seconds; 12.8 seconds at 107.9 mph; and 108 feet. Brembos and Pirellis did much for the Jeep's braking, but when it came to speed and stick, the twin-turbocharged Germans had the upper hand.
As you can imagine, hooning while hauling is spectacular fun, but since track testing with a trailer attached is highly dangerous, we set out on our full "time attack" challenge atop the 14-turn Streets of Willow sans cargo and mock family. It also takes time to get used to an SUV's mass on a relatively small and tight track such as Streets. Throw in these specimens' lust for speed, and you get a whole lot of stress on chassis, braking, and human components. With all that in mind, Mortara buckled into the X5 M.
Hunting a corner while riding a 5313-pound behemoth is a technical affair. Indeed, Mortara felt more push in the X5 M than he expected, but he noted that the ideally weighted helm, responsive chassis, and intuitive all-wheel drive programming produced an amazing sense of control and stability.
Williams observed a downshift hesitation from the six-speed when it was his turn to charge hard on track, likely an automatic "safe mode" response that preserves the engine's longevity. Upshifts, on the other hand, were as crisp, smooth, and quick as some dual-clutch units. He praised them as "preternatural" and loved the aforementioned M mode for "making him feel like Macho Man or Monster Man or Mega Man. The single button lets you know you have something special and you were pretty damn smart to make this purchase," he noted. All said and done, Mortara and the BMW posted a best time of 1 minute, 31.9 seconds.