A red tow truck towing two SUVs, a silver one on the truck's flatbed and a red one with two wheels on the groundYou've probably seen it: a massive RV cruising down the interstate with a Jeep Wrangler tethered to its rear bumper, merrily rolling away at 70 mph. It looks like a convenient way to carry your own adventure vehicle with your home on wheels. It's called "flat towing," a practice of pulling a vehicle with all four wheels on the ground. But if you're thinking of flat towing your AWD SUV, you'll be doing a lot more than towing it; you'll be killing it from the inside. To understand why flat towing kills AWD cars, and avoid reliving your worst tow truck experience, we need to understand the difference between AWD and 4WD. Traditionally, Four-Wheel-Drive (4WD) systems, like the ones on an old-school SUV, feature a mechanical transfer case with a "true neutral" setting. When you shift that transfer case into neutral, it physically disconnects the wheels from the transmission and the engine. This lets the wheels spin freely, and expensive bits inside the gearbox stay stationary. All-Wheel-Drive (AWD), however, is a much more sophisticated and fragile system. AWD systems are designed to distribute torque to all four wheels automatically. Unlike 4WD, most AWD systems never truly disconnect, as there is no "neutral" lever or button that severs the link between the rotating tires and the expensive gearbox internals.When you flat tow an AWD vehicle, its rolling wheels force the internal components of the drivetrain to spin. These components, however, are designed to be lubricated by an oil pump that only works when the engine is running. Without the engine on, you have metal-on-metal friction in the components spinning at highway speeds, with zero cooling and zero lubrication. The terrifying anatomy of a drivetrain meltdownA red AWD car being towed with a tow dollyIf you ignore your manual's warnings and drag your AWD Audi or Mercedes behind your Brabus Big Boy luxury RV, you're engaging in a very expensive experiment. Here's are the parts you'll most likely have to replace after your towing disaster. Most automatic transmissions rely on an internal fluid pump driven by the engine's input shaft. When the engine is off, the pump is off. But if the wheels are spinning, the output shaft is still turning the internal gears. Without fluid circulating to pull heat away, the friction will cause the clutches and gearsets to overheat and eventually seize.In an AWD system, the transfer case (or center differential) is the "brain" that balances power between the front and rear axles. These units often use viscous couplings or electronic clutch packs that are sensitive to heat. Then we have the driveshafts. While these are designed to spin, they aren't designed to spin for miles straight without the lubrication provided by a powered drivetrain. Modern AWD cars are tech-heavy. Most have electronic parking brakes that can self-engage if they detect the vehicle rolling without driver input. This can lead to the brakes dragging during the tow operation, which will not only ruin your brake pads and rotors but can also set the tires on fire. The right way to tow an AWD vehicleAn olive colored SUV being towed on a yellow flatbed truckThere's a lot you need to know before towing your car with an RV, especially if it has AWD. The only 100% safe way to tow an AWD vehicle is to flatbed it. With all four wheels off the road, the wheels and drivetrain remain completely stationary with no stresses acting on them. While flat-bedding your AWD vehicle, ensure the operator uses nylon wheel straps instead of metal J-hooks on your control arms. Modern suspensions are made of lightweight aluminium, which can bend.In an emergency, you can use dollies, but there's a catch. Using a standard tow dolly on only two wheels of an AWD car will destroy the center differential, because the other two wheels will be spinning at high speed. The only way to do this right is to use a "towing dolly" under the rear wheels with the front wheels lifted. These are small sets of wheels that create a makeshift trailer where all the wheels are off the ground. If possible, disconnecting the driveshaft is another way to safely tow your AWD vehicle. There are a handful of AWD vehicles, including some models of the Chevrolet Equinox and Honda CRV, that can be flat towed. However, these vehicles often require a complex ritual, and if you miss a single step, you could both kill the car and void your warranty. Unless you're driving a vehicle specifically engineered for flat towing, keep it off the ground while towing. A flatbed tow for $100-plus might sound expensive, but it's far cheaper than a $5,000 transmission rebuild. Want more like this? Join the Jalopnik newsletter to get the latest auto news sent straight to your inbox, and add us as a preferred search source on Google.
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