The driver of the slammed Honda S2000 in front of us saw a gap in traffic and nailed it, hoping we'd get off his back. We followed suit, with a slight nudge on the accelerator, just enough for the twin-turbos to unleash a wave of torque.
Entering a long left-hand sweeper that connected two of LA's freeways, the X5M on AccuAir air suspension took the mid-corner bumps with nonchalant ease, while the Honda was visibly disturbed, bouncing around the turn.
The S2000 driver is probably still wondering why he couldn't shake the SUV, which is what makes driving the X5M so entertaining. It defies the laws of physics.
For some purists, the X5M is also a conundrum. A 5300 lb SUV with a high center of gravity isn't generally the blueprint for the ultimate driving machine. Yet given what they had to work with, you must credit BMW's engineers for creating what is generally regarded, along with the X6M and Porsche Cayenne GTS, as one of the best handling performance SUVs on the road.
To improve on what comes off the showroom floor, you'd probably go the route of lowering the center of gravity with shorter springs and fitting wider tires.
In this case, the owner went with 295/30 R22 front and 335/25 R22 rear Pirelli Scorpions, giving a 20mm width increase over stock at each corner. For suspension, it rides on KW Variant 3 dampers but, instead of coil springs, it has AccuAir airbags to control roll, dive and squat.
AccuAir is one of the largest manufacturers of airbag suspension systems and a major player in the "bagger" scene, where the deeper drop and greater the tuck, the more respect you get.
The company's systems can be found on cars ranging from hot rods to newer VWs and Audis - the most popular European marques in the air-ride scene. And while the appearance is arresting, it brings up questions about daily drivability and how it affects ride and handling. And in the case of this X5M, how will it affect one of the best-handling SUVs.
Equipped with AccuAir's e-Level Air Management and UAS airbags over of the KW V3s, the BMW sits about 2.5" lower than stock on it regular setting at Level 2 (out of four).
The lowest setting is "All Down", when the airbags are completely deflated. Level 1 raises the car enough to cruise at low speed, but may affect the car's ability to take tight corners, depending on the clearance in the wheel wells. Level 2 is good for daily driving, while level 3 raises the car to clear obstacles, such as speed bumps or steep inclines.
To create an airbag system for the X5 M, the car was placed on AccuAir's suspension rig to measure the spring rates, front-to-rear ride frequency and roll rates. With those baseline figures, AccuAir aimed to stiffen it by about 30% at maximum travel.
The airbags behave similarly to progressive rate springs, getting stiffer the more they're compressed. And airbags are lighter than steel springs, shedding approximately 10 lb of unsprung weight per corner for better handling.
The e-Level system consists of an ECU to control the VU4 solenoid valve unit, height sensors, two 400c Viair air compressors and four Universal Air Suspension bags. A five-gallon tank, made from TIG-welded, anodized aluminum, maintains the air pressure. The compressor fills the tank, which is used as a reservoir to fill each bag as needed.
The cables, wiring, plugs and connectors are weatherproof and of the highest quality. The solenoids, compressors and other hard parts can be mounted on AccuAir's vibration-absorbing eXo mount. However, in this instance everything is hidden from sight under the trunk floor. Without sound deadening materials, the whirring and hissing was louder than a similar system mounted in a trunk, but it's not unbearable.
The ride height can be adjusted from the interior with a USB-connected e-Level touch pad. It allows pre-set adjustments or individual corners to be raised and lowered.
After you start the engine, you hear the bags adjusting the ride height. At stoplights, you can feel the self-leveling sensors making small adjustments to wherever it's needed. And on Downtown LA's deteriorating city streets, the X5M was firm but not punishing. In fact, it was what you'd expect from any suspension dropped 2.5" on firmer springs. Yet there was enough suspension travel to absorb smaller bumps and dips. Larger potholes called for a wide berth to preserve the 22" AG F140 forged three-piece wheels.
On the freeway, there was some jiggling over high-frequency road seams, which again is what you'd expect on conventional coilovers...
Once we picked up speed, and the road started to twist, the X5M attacked corners with the sort of eagerness you'd expect from this car, so that quality hadn't been lost.
The airbags and KWs kept body roll at a minimum and, on a few cloverleaf on-ramps taken at ridiculous speeds, the car remained stable and planted, providing the confidence a driver needs to explore the limits.
So what we discovered was that AccuAir's air suspension rides and handles in a similar way to conventional coilovers. The big advantage you have is being able to raise it to clear obstacles, or lower it to put on show. Many people may not need this ability, but for those who do, air suspension is winning new fans daily.
This particular X5M received fortification under the hood by way of a mildly-ported F10 M5 turbo manifold. Our friends at BBi Autosport in Huntington Beach, CA, made the swap and also tuned the ECU.
The twin-turbo V8 also received 3" cat-less downpipes from AR Design, that feed into a titanium Akrapovic cat-back exhaust, terminating in carbon fiber tips. BBi claims power is now close to 700hp on pump gas - a significant bump from the stock engine's 555hp.
In fact, it only takes the slightest poke on the pedal to achieve warp drive. The V8's wide plateau of torque means there's virtually no waiting. The six-speed M Sport automatic responds with quick downshifts when left in automatic mode, or you can control the madness via the paddle shifters.
The engine also responds with a surly, full-throated snarl through the open downpipes, while the Akrapovic exhaust issues a ferocious howl from the rear.
The sling-shot sensation of moving 2.5 tons of high-grade German steel so rapidly down the road might seem unsettling if it weren't for the effectiveness of the massive stock brakes.
The interior received a $5000 makeover of alcantara on the headliner and pillars, with seams stitched in the BMW Motorsport colored thread to match the steering wheel.
On the outside, the car was de-chromed, with the grilles, mirror mounts and kidney grilles all painted gloss black. Vorsteiner's carbon fiber front spoiler and rear diffuser add a touch of aggression at either end and, because the owner wanted to be different, all the glass is non-tinted European-spec (a $3500 conversion!).
If I hadn't been told that the car was on airbags, I would have thought it was simply on stiffer suspension. It's genuinely hard to tell the difference, with really only the sound of the compressors giving the game away.
AccuAir managed to retain and maybe enhance the X5M's best quality, that of a great handling SUV, without losing its daily drivability. It's still more tossable than 5300 lb should be, and was never surprised or overwhelmed by high-g turns.
So the impression of how airbag suspension affects performance is positive. With its lower center of gravity, slightly wider tires and progressive-rate airbags, we wouldn't be surprised if this car out-performed a stock X5M on a skidpad or through the cones. Score one for the baggers.
2012 BMW X5M
Engine 4.4-liter S63B44 V8 DOHC bi-turbo with ported F10 M5 turbo manifold and software from BBi Autosport, 3" AR Design cat-less downpipes, titanium Akrapovic cat-back exhaust with carbon fiber tips
Brakes stock, painted calipers
Suspension AccuAir Universal Air Suspension bags, KW Variant 3 adjustable dampers, e-Level Air Management, VU4 solenoid unit, height sensors, two 400c Viair compressors, five-gallon tank
Wheels & Tires 10.5x22" f, 12.5x22" r Avant Garde F140 three-piece, step-lip wheels, 295/30 R22 f, 335/25 R22 r Pirelli Scorpion tires
Exterior Vorsteiner carbon fiber front lip and rear diffuser, gloss black kidney grilles, lower grille and mirror mounts
Interior alcantara headliner and pillars with M-colored stitching, European-spec non-tinted glass