To maximize occupant safety, the front seat shoulder belts of the BMW M4 have pretensioners to eliminate dangerous slack in the event of a collision and force limiters to limit the pressure the belts will exert on the passengers. The Toyota Supra doesn’t offer pretensioners.
The M4’s pre-crash front seatbelts will tighten automatically in the event the vehicle detects an impending crash, improving protection against injury significantly. The Supra doesn’t offer pre-crash pretensioners.
The M4 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 Supra 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 M4 Competition offers all-wheel drive to maximize traction under poor conditions, especially in ice and snow. The Supra doesn’t offer all-wheel drive.
The M4 offers an optional Surround View to allow the driver to see objects all around the vehicle on a screen. The Supra 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 M4 has a standard blind spot warning system that 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 Supra’s blind spot costs extra.
To help make backing out of a parking space safer, the M4 has standard Cross Traffic Warning, helping the driver avoid collisions. Toyota charges extra for Rear Cross Traffic Alert on the Supra.
Both the M4 and the Supra have standard driver and passenger frontal airbags, front side-impact airbags, driver and front passenger knee airbags, side-impact head airbags, four-wheel antilock brakes, traction control, electronic stability systems to prevent skidding, crash mitigating brakes, daytime running lights, lane departure warning systems, rearview cameras and driver alert monitors.
The BMW M4 weighs 430 to 1125 pounds more than the Toyota Supra. The NHTSA advises that heavier cars are much safer in collisions than their significantly lighter counterparts.