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Both the S8 and RLX have child safety locks to prevent children from opening the rear doors. The S8 has power child safety locks, allowing the driver to activate and deactivate them from the driver's seat and to know when they're engaged. The RLX’s child locks have to be individually engaged at each rear door with a manual switch. The driver can’t know the status of the locks without opening the doors and checking them.
The S8 has a standard front seat center airbag, which deploys between the driver and front passenger, protecting them from injuries caused by striking each other in serious side impacts. The RLX doesn’t offer front seat center airbags.
The S8 has a standard Secondary Collision Brake Assist, which automatically applies the brakes in the event of a crash to help prevent secondary collisions and prevent further injuries. The RLX doesn’t offer a post collision braking system: in the event of a collision that triggers the airbags, more collisions are possible without the protection of airbags that may have already deployed.
To provide maximum traction and stability on all roads, All-Wheel Drive is standard on the S8. But it costs extra on the RLX.
A passive infrared night vision system optional on the S8 helps the driver to more easily detect people, animals or other objects in front of the vehicle at night. Using an infrared camera to detect heat, the system then displays the image on a monitor in the dashboard and even aims one of the vehicle’s headlights in the direction of the person or object. The RLX doesn’t offer a night vision system.
Both the S8 and the RLX have standard driver and passenger frontal airbags, front side-impact airbags, driver knee airbags, side-impact head airbags, front seatbelt pretensioners, height adjustable front shoulder belts, four-wheel antilock brakes, traction control, electronic stability systems to prevent skidding, crash mitigating brakes, daytime running lights, lane departure warning systems, rearview cameras, available blind spot warning systems and rear cross-path warning.
The Audi S8 weighs 922 to 1325 pounds more than the Acura RLX. The NHTSA advises that heavier cars are much safer in collisions than their significantly lighter counterparts.
The S8’s corrosion warranty is 7 years longer than the RLX’s (12 vs. 5 years).
There are over 11 percent more Audi dealers than there are Acura dealers, which makes it easier should you ever need service under the S8’s warranty.
A hardened steel chain, with no maintenance needs, drives the camshafts in the S8’s engine. A rubber cam drive belt that needs periodic replacement drives the RLX’s camshafts. If the RLX’s belt breaks, the engine could be severely damaged when the pistons hit the opened valves.
J.D. Power and Associates’ 2019 Initial Quality Study of new car owners surveyed provide the statistics that show that Audi vehicles are better in initial quality than Acura vehicles. J.D. Power ranks Audi 22nd in initial quality. With 4 more problems per 100 vehicles, Acura is ranked 24th.
J.D. Power and Associates’ 2019 survey of the owners of three-year-old vehicles provides the long-term dependability statistics that show that Audi vehicles are more reliable than Acura vehicles. J.D. Power ranks Audi 8th in reliability, above the industry average. With 47 more problems per 100 vehicles, Acura is ranked 26th.
From surveys of all its subscribers, Consumer Reports’ December 2019 Auto Issue reports that Audi vehicles are more reliable than Acura vehicles. Consumer Reports ranks Audi 14 places higher in reliability than Acura.
The S8’s 4.0 turbo V8 hybrid produces 253 more horsepower (563 vs. 310) and 318 lbs.-ft. more torque (590 vs. 272) than the RLX’s standard 3.5 SOHC V6. The S8’s 4.0 turbo V8 hybrid produces 186 more horsepower (563 vs. 377) and 249 lbs.-ft. more torque (590 vs. 341) than the RLX Sport Hybrid’s standard 3.5 SOHC V6 hybrid.
The S8 has 6.6 gallons more fuel capacity than the RLX Sport Hybrid’s standard fuel tank (21.7 vs. 15.1 gallons), for longer range between fill-ups. The S8 has 3.2 gallons more fuel capacity than the RLX’s standard fuel tank (21.7 vs. 18.5 gallons).
For better stopping power the S8’s brake rotors are larger than those on the RLX:
RLX Sport Hybrid
The S8’s standard front and rear disc brakes are vented to help dissipate heat for shorter stops with less fading. The rear discs on the RLX are solid, not vented.
The S8 offers optional heat-treated ceramic brake rotors, which last ten to twenty times as long as conventional cast iron rotors, don’t rust, don’t fade during repeated high speed braking, and their lighter weight contribute to better braking, handling and acceleration. The RLX doesn’t offer ceramic brake rotors.
For better traction, the S8 has larger tires than the RLX (265/40R20 vs. 245/40R19).
The S8’s optional tires provide better handling because they have a lower 35 series profile (height to width ratio) that provides a stiffer sidewall than the RLX’s 40 series tires.
For better ride, handling and brake cooling the S8 has standard 20-inch wheels. Only 19-inch wheels are available on the RLX. The S8 offers optional 21-inch wheels.
The S8 has a standard space-saver spare tire so you can replace a flat tire and drive to have the flat repaired or replaced. A spare tire isn’t available on the RLX; it requires you to depend on roadside assistance and your vehicle will have to be towed.
The front and rear suspension of the S8 uses air springs for a smoother, controlled ride than the RLX, which uses coil springs. Air springs maintain proper ride height and ride more smoothly.
The S8 has a standard driver-adjustable suspension system. It allows the driver to choose between an extra-supple ride, reducing fatigue on long trips, or a sport setting, which allows maximum control for tricky roads. The RLX’s suspension doesn’t offer adjustable shock absorbers.
The S8 has a standard automatic front and rear load leveling suspension to keep ride height level with a heavy load or when towing. The S8’s height leveling suspension allows the driver to raise ride height for better off-road clearance and then lower it again for easier entering and exiting and better on-road handling. The RLX doesn’t offer a load leveling suspension.
For a smoother ride and more stable handling, the S8’s wheelbase is 11 inches longer than on the RLX (123.2 inches vs. 112.2 inches).
The S8 has .7 inches more front headroom, 1.6 inches more rear headroom, 5.5 inches more rear legroom and .6 inches more rear shoulder room than the RLX.
For enhanced passenger comfort on long trips the S8’s available rear seats recline. The RLX’s rear seats don’t recline.
To make loading and unloading groceries and cargo easier when your hands are full, the S8’s power trunk can be opened or closed just by kicking your foot under the back bumper, leaving your hands completely free. The RLX doesn’t offer a power or hands-free opening trunk.
The engine in the S8 is mounted longitudinally (North-South), instead of sideways, as in the RLX. This makes it easier to service and maintain, because there are no rear spark plugs and the accessory belts are in front.
Unlike the driver-only memory system in the RLX, the S8 has standard driver and passenger memory, so that when drivers switch, the memory setting adjusts the driver’s seat, steering wheel position and outside mirror angle and the front passenger seat also adjusts to the new passenger’s preset preferences.
The power windows standard on both the S8 and the RLX have locks to prevent small children from operating them. When the lock on the S8 is engaged the driver can still operate all of the windows, for instance to close one opened by a child. The RLX prevents the driver from operating the other windows just as it does the other passengers.
In poor weather, headlights can lose their effectiveness as grime builds up on their lenses. This can reduce visibility without the driver realizing. The S8 offers available headlight washers to keep headlight output high. The RLX doesn’t offer headlight washers.
To help drivers avoid possible obstacles, the S8 has standard cornering lights to illuminate around corners when the turn signals are activated. The RLX doesn’t offer cornering lights. The S8 also offers optional adaptive headlights to illuminate around corners automatically by reading vehicle speed and steering wheel angle.
The S8 has standard front air-conditioned seats and offers them optionally in the rear. This keeps the passengers comfortable and takes the sting out of hot seats in summer. The RLX doesn’t offer air-conditioned seats in the rear.
The S8 has a standard heated steering wheel to take the chill out of steering on extremely cold winter days before the car heater warms up. A heated steering wheel is only available on the RLX Sport Hybrid.
The S8 has standard massaging front and optional massaging rear seats. Massaging seats aren’t available in the RLX.
To quickly and conveniently keep personal devices charged without cables tangling and wearing out, the Audi S8 has a standard wireless phone charging system (Qi) in the center console. The RLX doesn’t offer wireless personal charging.
The S8 offers an optional 115-volt a/c outlet on the center console, allowing you to recharge a laptop or run small household appliances without special adapters that can break or get misplaced. The RLX doesn’t offer a house-current electrical outlet.
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