The X4’s pre-crash front seatbelts will tighten automatically in the event the vehicle detects an impending crash, improving protection against injury significantly. The Forester doesn’t offer pre-crash pretensioners.
The BMW X4 has standard driver and front passenger side knee airbags mounted low on the dashboard. These airbags helps prevent the driver and front passenger from sliding under their seatbelts or the main frontal airbags; this keeps them better positioned during a collision for maximum protection. Knee airbags also help keep the legs from striking the dashboard, preventing knee and leg injuries in the case of a serious frontal collision. The Forester doesn’t offer a front passenger side knee airbag.
The X4 has a standard PostCrash iBrake, which automatically applies the brakes in the event of a crash to help prevent secondary collisions and prevent further injuries. The Forester 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.
The X4 offers an optional Surround View to allow the driver to see objects all around the vehicle on a screen. The Forester only offers a rear monitor and front and rear parking sensors that beep or flash a light. That doesn’t help with obstacles to the sides.
The X4 has a standard blind spot warning system which uses sensors to alert the driver to objects in the vehicle’s blind spots where the side view mirrors don’t reveal them and moves the vehicle back into its lane. A system to reveal vehicles in the Forester’s blind spot costs extra.
To help make backing out of a parking space safer, the X4 has a standard rear cross-path warning system, which uses sensors in the rear bumper to alert the driver to vehicles approaching from the side, helping the driver avoid collisions. Rear cross-path warning costs extra on the Forester and isn't available on the not available.
Compared to metal, the X4’s plastic fuel tank can withstand harder, more intrusive impacts without leaking; this decreases the possibility of fire. The Subaru Forester has a metal gas tank.
Both the X4 and the Forester have standard driver and passenger frontal airbags, front side-impact airbags, driver knee airbags, side-impact head airbags, front seatbelt pretensioners, four-wheel antilock brakes, all wheel drive, traction control, electronic stability systems to prevent skidding, crash mitigating brakes, daytime running lights, lane departure warning systems and rearview cameras.
The BMW X4 weighs 558 to 949 pounds more than the Subaru Forester. The NHTSA advises that heavier vehicles are much safer in collisions than their significantly lighter counterparts.