The i8 has standard City Collision Mitigation, which use forward mounted sensors to warn the driver of a possible collision ahead. If the driver doesn’t react and the system determines a collision is imminent, it automatically applies the brakes at full-force in order to reduce the force of the crash or avoid it altogether. The 918 doesn't offer collision warning or crash mitigation brakes.
The i8 has a standard Side and Top View Cameras to allow the driver to see objects all around the vehicle on a screen. The 918 only offers a rear monitor.
The i8 has standard BMW Assist, which uses a global positioning satellite (GPS) receiver and a cellular system to remotely unlock your doors if you lock your keys in, help track down your vehicle if it’s stolen or send emergency personnel to the scene if any airbags deploy. The 918 doesn’t offer a GPS response system, only a navigation computer with no live response for emergencies, so if you’re involved in an accident and you’re incapacitated help may not come as quickly.
Both the i8 and the 918 have standard driver and passenger frontal airbags, front side-impact airbags, side-impact head airbags, front seatbelt pretensioners, four-wheel antilock brakes, all-wheel drive, traction control and electronic stability systems to prevent skidding.
The i8’s corrosion warranty is 2 years longer than the 918’s (12 vs. 10 years).
BMW pays for scheduled maintenance on the i8 for 4 years and 50,000 miles. BMW will pay for oil changes, lubrication and any other required maintenance. Porsche doesn’t pay scheduled maintenance for the 918.
There are over 74 percent more BMW dealers than there are Porsche dealers, which makes it much easier should you ever need service under the i8’s warranty.
On the EPA test cycle the i8 gets better fuel mileage on a full charge than the 918 on a full charge (76 vs. 67 MPGe Combined).
On the EPA test cycle the i8 gets better fuel mileage running its gasoline engine than the 918 running its gasoline engine (28 city/29 hwy vs. 20 city/24 hwy).
The i8’s maximum driving range in pure electric mode is 22 miles, 22% further than the 918’s 18 mile range.
In an emergency stopping situation, many drivers don’t press the brakes with enough force to stop the vehicle in the shortest distance. The i8 has a standard brake assist system to detect emergency braking situations (by how hard and how quickly the brake pedal is pressed) and then automatically apply maximum braking immediately in order to help prevent a collision. The 918 doesn’t offer a brake assist feature.
For a smoother ride and more stable handling, the i8’s wheelbase is 2.7 inches longer than on the 918 (110.2 inches vs. 107.5 inches).
For better handling and stability, the track (width between the wheels) on the i8 is 4 inches wider in the rear than on the 918.
The i8’s front to rear weight distribution is more even (48.7% to 51.3%) than the 918’s (43% to 57%). This gives the i8 more stable handling and braking.
For better maneuverability, the i8’s turning circle is 1.3 feet tighter than the 918’s (40.4 feet vs. 41.7 feet).
The BMW i8 may be more efficient, handle and accelerate better because it weighs about 350 pounds less than the Porsche 918.
The design of the BMW i8 amounts to more than styling. The i8 has an aerodynamic coefficient of drag of .26 Cd. That is significantly lower than the 918 (.36). A more efficient exterior helps the i8 go faster and keeps the interior quieter. It also helps the i8 get better fuel mileage.
The i8 has standard seating for 4 passengers; the 918 can only carry 2.
The i8 has 4.7 inches more front headroom, .1 inches more front legroom and 7.2 inches more front shoulder room than the 918.
The i8 has a standard remote vehicle starting system, so the vehicle can be started from inside the driver's house. This allows the driver to comfortably warm up the engine before going out to the vehicle. The climate system will also automatically heat or cool the interior. The 918 doesn’t offer a remote starting system.
The i8’s standard tilting steering column adjusts to different sized drivers and makes entering and exiting easier. Porsche doesn’t offer tilt steering on the 918.
When two different drivers share the i8, the memory system makes it convenient for both. Each setting activates different, customized memories for the driver’s seat position, outside mirror angle, climate settings and radio stations. The 918 doesn’t offer a memory system.
While driving with high beams on, sensitive light sensors standard on the i8 detect other vehicles which could be blinded and automatically switch to low beams. The 918 doesn’t offer automatic dimming high beams.
The i8 has standard heated front seats, which keep the driver and front passenger extremely comfortable in the winter. Heated seats aren’t available in the 918.
The i8 was chosen as one of Automobile Magazine’s “All Stars” in 2015. The 918 has never been an “All Star.”