2021 Ford Bronco “H.O.S.S.” Suspension Explained
At this year’s Woodward Dream Cruise, Ford’s focus was squarely on Broncos old and new, with new and first-generation Broncos to drive plus a rolling chassis for show and tell. Ford suspension engineers used it to tell us their side of the story as to which off-road icon has the better suspension concept—the Ford Bronco or Jeep Wrangler. Of course, in either case we’re talking about the top-dog models: Jeep Wrangler Rubicon versus the Ford Bronco with the H.O.S.S. (High-speed Off-road Suspension System) with Bilstein position-sensitive dampers and stabilizer disconnect system, standard on Badlands and First Edition models, plus the big-tire Sasquatch package.
Bronco IFS versus Jeep Live Axle
Advantages of Ford’s independent front suspension include a reduction in unsprung mass of 40 percent and the ability to utilize rack-and-pinion steering. Lowering unsprung mass makes it easier for the dampers to control wheel motions, especially when traveling at speed over desert whoops. As a result, the tires spend more of the time pressed firmly to the ground. And the advantages of rack-and-pinion over recirculating-ball include improved steering feel and electric power assist, which makes it easier to offer variable assist levels tailored to different driving modes. This system is also used to provide damping to counteract kickback to varying degrees depending on the drive mode selected. Baja and Sand modes get unique steering damping curves.
Electrohydraulic Stabilizer-Bar Disconnect
Most stabilizer bar disconnects (or “sway bar” disconnects, if you’re not a stickler for semantics) use some sort of sliding collar to connect and disconnect the bar somewhere near its middle. This is a simple and effective approach, but this design typically can’t operate (connect or disconnect) while the wheels are articulated. So if you suddenly find yourself running out of wheel travel mid-obstacle, you need to back down to a flat area to disconnect. The Bronco’s electrohydraulic system (produced by BWI, the Magneride folks) can be disconnected any time, and when you request a reconnect, it automatically connects the next time the bar straightens out for an instant.
Here’s how it works: When disconnected, one end of the bar is free to rotate relative to the other, and as it rotates it moves inboard and outboard, guided by bearings in a screw-jack, moving a hydraulic piston in the process (the linkage connecting the bar with the control arm easily accounts for this motion). Fluid flows from either side of this piston in and out of a second chamber with another sliding piston. This is the control piston. Travel above 20 mph or press the button to reconnect the bar, and when this control piston passes through the center of its travel, a pin locks it in place, freezing the larger piston and locking the ends of the anti-roll bar together. Flow restrictors in the lines connecting these cylinders provide damping, so that if a wheel is up on a rock and you disconnect, the body won’t suddenly slam down. The system also includes internal hydraulic diagnostics that can alert the driver to any faults more easily than electromechanical systems can.
Engage “Rock Crawl” mode in the Bronco, and the bar will automatically disconnect whenever the speed drops below 25 mph, reconnecting automatically above 20 mph, but of course DIY drivers can press buttons to make this happen if they prefer (all of which feeds into the Bronco’s stated aim to “flatter the novice; reward the expert”). When connected, the control device rotates with the bar, and the bar behaves like a solid 33mm (1.3-inch) bar.
Rear Suspension Setup
Four links and a Panhard rod locate the live axle, with the coils and dampers mounted as far outboard as possible to afford maximum mechanical advantage. This permits increased roll control with lower spring/damper rates (there is no rear stabilizer bar). The lower rear spring rates improve pitch sensitivity, allowing the truck to remain flat on jumps. Ford claims class-leading overall suspension travel of 8.7 inches front, 10.2 inches rear on the 33-inch tires. (Opting for the larger 35s adds 0.4 inch, but restricts jounce travel slightly.)
Bilstein Position-Sensitive Dampers
Optional across the board, the Bilstein position-sensitive true monotube dampers replace the base Hitachi twin-tube dampers, providing three zones of varying damping rates with nitrogen-charged remote reservoirs. They’re softest in the middle to allow small imperfections to be absorbed easily. As the wheels approach the end of their travel in either jounce or rebound, “end-stop control valves” engage, with an additional piston supported by a coil spring designed to ramp up the damping rate at each end by 3-5 times what it is in the center.
All Broncos ostensibly get H.O.S.S. tuning, but the Bilstein position-sensitive dampers, stabilizer disconnect, and Sasquatch packages cost extra. On the base, Big Bend, Black Diamond, and Outer Banks trims, the Bilsteins come bundled with the higher ride height and big tires of the Sasquatch package for between $4,200 and $4,995 depending on trim. The Bilstein PSD dampers come standard on Badlands, Wildtrak, and First Edition models, the latter two of which also get the high-clearance suspension and big Sasquatch tires standard (they add $2,495 to Badlands models). The stabilizer bar disconnect system is only available on the Badlands and First Edition models (at least for now), where it is standard equipment on those trims.
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