Too often, for too many drivers, speed is the primary concern. “Zero-to-sixty in X seconds!” ”Top engine speed (”How fast can she go?”).” But for most drivers, and even professional racers (for whom speed is a major factor), the better question to ask is, “How long does it take to stop if you’re travelling at 100 mph or higher?!”
Vehicle speeds are a crucial factor in overall traffic safety and accidents, fatal or otherwise. The U.S. Department of Transportation National Highway Traffic Safety Administration (NHTSA) has estimated that speeding is involved in approximately 28% of fatal motor vehicle crashes (2014 data). (The same report says that in that same year only 13 percent of speeding-related fatalities occurred on interstate highways.)
“Speeding” or “excessive speed” means a driver is going too fast to control the vehicle, appropriate to weather and road conditions, and traffic situations, including traffic volume and pedestrian and bicycle traffic. Speed directly affects a driver’s perception and reaction time, and critically, braking distance, that is, how far a vehicle will travel from the point when the brakes are fully applied to when it comes to a complete stop. Braking distance plus reaction distance–speed combined with the operator’s perception/reaction time–equals total stopping distance.
As a rough example, driving at an initial velocity of 60 mph on a dry surface, it would take approximately 6.87 seconds (including a 1 second delay for driver reaction) and a total stopping distance of 302.28 feet (> 92 meters)–longer than a football field!–to decelerate and stop your car.
So, speed, control, reaction time, and other motorists and pedestrians are among a driver’s constant challenges. The solution is to act upon the crucial element of shortening a vehicle’s braking/stopping distance–because short, sure stopping of a fast-moving, powerful vehicle is a major, life-saving key to improved road safety.
Development of these systems and components is within the scope of the automotive and transportation industries themselves–they are a major focus of automobile, motorcycle and truck manufacturers (original equipment manufacturers, referred to as “OEMs”), universities, and engineering and R&D centers worldwide.
But wider measures to implement greater road and traffic safety should be placed at a priority level much higher than has been the case thus far. Government bodies (e.g., the multi-pronged European Commission ‘CARS 2020 Action Plan,’ U.S. Federal and State highway administrations, local law jurisdictions and enforcement entities) issue and administer vehicular and traffic laws and guidelines. But these same responsible entities should also take targeted action to institute, upgrade and monitor regulations regarding high-performance braking systems (including brake fluids) and vehicular wheel weight–action to make high-performance braking systems mandatory and to govern the maximum weight of road wheels, especially aftermarket upgrades.
Brake discs/rotors, calipers, and complete state-of-the-art braking systems (available as original equipment or as aftermarket replacements), made at superior levels of technology and reliability, are often called the most safety-critical parts of any moving vehicle. For example, independently owned and managed EBC Brakes (the UK and U.S.) says, “A high performance brake pad will be one which has good friction level and pedal feel on first application and can hold this level of performance throughout the whole braking cycles.” Brakes must not “fade” or fail under the heat of braking. Not only must high performance brakes work effectively under heat and load they must have good durability (enhanced by additives such as copper or coke blended into pads).
Quality, higher-spec brake fluids are also key to better brakes–most fluids are hygroscopic (they readily absorb moisture), so a higher-grade, more efficient brake fluid is needed to keep brakes operating at a maximum.
High-performance brakes incorporate rotors made of cast iron (like Gray iron, which has high thermal conductivity and specific heat capacity) or from virgin alloy ingot rather than reprocessed irons which are common in 99% of aftermarket brakes. Brakes convert kinetic energy into heat energy. Poor materials or poorly made brakes can overheat and fade, and rotors can develop cracks due to metal fatigue. For highest possible performance calipers can be forged instead of cast.
Now how does wheel weight factor in this speed/safety/braking equation?
Together with a brake system that provides optimum stopping performance, lighter wheels measurably improve the resulting distance. Installing large cast wheels (above 20″ e.g.) overloads both the suspension and the brake system (neither of which has been designed or tested/homologated for this double-load), unless upgraded–and may considerably increase braking distance as a result. This negatively impacts the safety of not only respective drivers themselves, but also passengers and pedestrians, who become inevitably faced with sub-standard vehicle performance, outside of certified and regulated standards. When automotive OEMs test and certify their vehicles and assess braking distance, the wheels deployed at the time are quite different than a heavier version that may eventually find its way onto a vehicle. Consequently, when larger and heavier cast wheels are installed their mass may be twice as high as what the vehicle was designed and built for. Lightweight, strong forged wheels (the very lightest being forged magnesium wheels), are a significant part of a car’s unsprung weight–the combined weight of the wheels and all the parts fastened to them (including tires and brake system elements). The weight of other elements held above ground by the suspension is referred to as sprung weight.
The ratio of sprung to unsprung weight is important: the force exerted by the unsprung components from the bottom upwards must be offset by the sprung weight. If not, the vehicle loses its road grip, which adversely affects its steerability. Wheel weight also affects vehicle dynamics. The heavier the wheels, the more energy and time are required to alter their rotation speed. Reducing unsprung weight (i.e., with lightweight wheels) enhances dynamics, and contributes to a smooth, more controlled ride on a wide range of road surfaces.
Drivers looking for bigger, more impressive-looking wheels must remember: lightweight wheels perform better. Bigger cast wheels are heavier wheels, and heavier wheels are harder to control. Companies like SMW Engineering, a leading manufacturer of lightweight high-performance forged magnesium wheels, are at the forefront of researching the effect of wheel mass on vehicle performance and safety.
“It is an imperative step toward saving lives,” says Marks Lisnanskis, SMW Chairman.
Magnesium has the highest strength-to-weight ratio of all commonly available metals, and is impressively light–magnesium wheels are 20% lighter than forged aluminum wheels and up to 40% lighter than regular cast alloy wheels, at the same load factor. “Additionally, magnesium has a superior damping capacity (the ability to absorb impacts and vibrations),” says Mr. Lisnanskis, “as well as a high heat dissipation capacity– magnesium alloy wheels help the brakes cool faster and prevent overheating, which is especially important if emergency braking is required at a high speed.”