What are Portal Axles?
These trick axles give off-roaders the ability to climb over boulders.
Mercedes-Benz
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Despite their name, portal axles can't help you reach another dimension. They can, however, increase a dimension that's very important for off-roading: ground clearance. We'll explain what portal axles are, why someone would want them, and how to get them.
What are Portal Axles?
While a standard axle exists in a straight line—wheel, shaft, differential, shaft, wheel—a portal axle makes a couple of turns between the shafts and wheels, dropping the wheels down lower and effectively lifting the vehicle's body and axle higher off the ground in the process. That redirection comes courtesy of geared hubs, which carry the output from the elevated axle/differential down to the wheels.
Why Would Someone Want Portal Axles?
Because a traditional axle is usually the lowest part under a vehicle, it determines the ground clearance. Raise the axle and you increase ground clearance, freeing up the space between the wheels for large rocks, fallen trees, and other inanimate objects you might encounter out on the trail. For this reason, portal axles are popular with off-roaders who want to tackle obstacle-laden terrain. You'll also find them on some military rigs (Humvees, Pinzgauers), tractors, and a handful of civilian vehicles (many of them descended from military rigs).
Moreover, geared hubs can take stress off the rest of the driveline by serving gear-reduction duty (aka torque amplification) at the wheels. Because of this, the rest of the driveline components (driveshaft, axle shafts, differential) don't need to be as strong as the factory setup, and someone could ostensibly replace them with less robust, lighter-weight parts, were they so inclined.
One interesting exception to the portal-axles-sit-above-the-wheel-centerline rule is the 2010 Porsche 911 GT3 R Hybrid. For this race car, Porsche used a form of portal axle at the front to situate the "axle" (actually a pair of electric motors) below the wheel centerline for packaging reasons. This also helped lower the car's center of gravity.
How Much Do Portal Axles Cost?
If you're interested in installing portal axles on your rig, you'll need to turn to the aftermarket, where there are kits available for many serious SUVs and trucks. They aren't cheap. As an example, one such conversion kit for the current Jeep Wrangler will set you back more than $13,000 before labor, and that's using the stock axles with new portal gearboxes at each corner.
Automakers rarely offer portal axles as a factory option, but it's not unheard of. Mercedes used to install them on a version of the last-gen G-wagen SUV, called the G550 4x4 Squared. It started at about $225,995, considerably more than the regular G550's base price of about $123,395. We expect Mercedes-AMG to bring back the 4x42 soon but as a G63, with more power and an even higher price than its predecessor. It's an expensive route to portal axles, to be sure, but at least you get a really swanky SUV to go with them.
