Both the SL Class and the 3 Series Convertible have standard driver and passenger frontal airbags, front side-impact airbags, head airbags, front seatbelt pretensioners, height adjustable front shoulder belts, four wheel antilock brakes, traction control and electronic stability systems to prevent skidding.
The SL Class has more powerful engines than the 3 Series Convertible:
Horsepower |
Torque |
|
SL550 5.5 DOHC V8 |
382 HP |
391 lbs.-ft. |
SL55 AMG 5.4 supercharged V8 |
510 HP |
531 lbs.-ft. |
SL600 5.5 turbo V12 |
510 HP |
612 lbs.-ft. |
SL65 AMG 6.0 turbo V12 |
604 HP |
738 lbs.-ft. |
328i Convertible 3.0 DOHC 6 cyl. |
230 HP |
200 lbs.-ft. |
335i Convertible 3.0 turbo 6 cyl. |
300 HP |
300 lbs.-ft. |
An engine control system which can shut down half of the engine’s cylinders helps improve the SL Class V12’s fuel efficiency. The 3 Series Convertible doesn’t offer a system which can shut down part of the engine.
The SL Class has 5 gallons more fuel capacity than the 3 Series Convertible (21.1 vs. 16.1 gallons), for longer range between fill-ups.
For better stopping power the SL Class’ brake rotors are larger than those on the 3 Series Convertible:
SL550 |
SL65 AMG |
328i Convertible |
335i Convertible |
|
Front Rotors |
13.8 inches |
15.4 inches |
12.3 inches |
13.7 inches |
Rear Rotors |
12.6 inches |
14.2 inches |
11.8 inches |
13.2 inches |
For better traction, the SL Class has larger tires than the 3 Series Convertible (F:255/40R18 & R:285/35R18 vs. 225/45R17). The SL Class’ tires are larger than the largest tires available on the 3 Series Convertible (F:255/40R18 & R:285/35R18 vs. F:225/40R18 & R:255/35R18).
The SL Class’ standard 255/40R18 front and 285/35R18 rear tires provide better handling because they have a lower 40 series front and 35 series rear profile (height to width ratio) which provides a stiffer sidewall than the 328i Convertible’s standard 45 series tires. The SL55/SL65’s 255/35R19 front and 285/30R19 rear tires have a lower 35 series front and 30 series rear profile than the 3 Series Convertible’s optional 40 series front and 35 series rear tires.
For better ride, handling and brake cooling the SL Class has standard 18 inch wheels. Smaller 17 inch wheels are standard on the 328i Convertible. The SL55/SL65’s 19 inch wheels are larger than the 18 inch wheels optional on the 3 Series Convertible.
The SL Class 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 3 Series Convertible, it requires you to depend on its run-flat tires, which limits mileage and speed before they are repaired. If a run-flat is damaged beyond repair by a road hazard your vehicle will have to be towed. Some models of the 3 Series Convertible don’t even offer run-flats.
The SL Class offers an available adjustable active suspension system, which counteracts cornering forces actively, limiting body roll and improving handling and stability. BMW doesn’t offer an active suspension on the 3 Series Convertible.
The SL Class 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 3 Series Convertible’s suspension doesn’t offer adjustable shock absorbers.
The SL Class has a standard automatic front and rear load leveling suspension to keep ride height level with a heavy load or when towing. The 3 Series Convertible doesn’t offer a load leveling suspension.
For better handling and stability, the average track (width between the wheels) on the SL Class is 2.5 inches wider in the front and 1.2 inches wider in the rear than the track on the 3 Series Convertible.
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