How Does Wheel Weight Affect Car Performance?
It is fairly common to see drivers change the OEM wheels to fancier wheels to give the vehicle a fresh new look. Other than the aesthetics and design of the wheel it is important to purchase wheels that are lighter or of the same weight as the OEM wheels. This is because the weight of the wheels could have a major impact on your vehicle. Let's get into it.
Why Are Lightweight Wheels Important?
Wheel weight becomes part of your vehicle’s overall weight. Heavier cars need more engine power to accelerate and more braking power to decelerate. It might also impact the overall fuel consumption of the vehicle.
Some benefits of lighter weight wheels are:
- Quicker acceleration and efficient braking with reduced brake wear
- More responsive handling on turns
- Quick regain of grip over uneven or bumpy surfaces
- Reduced strain on suspension springs, shock absorbers, and other suspension parts
Sprung Weight & Unsprung Weight
Sprung weight: It is the weight of the vehicle that is directly supported by the suspension system. This includes the motor, chassis, transmission, body, and interior, as well as the cargo and passengers.
Unsprung weight: It is the weight of the vehicle that is not supported by the suspension system. This consists of axles, wheels, tires, hubs, brakes, assemblies, differential, and anything directly connected to the wheels.
Weight Distribution In A Wheel
Weight distribution in the wheel can have a serious impact on performance and handling characteristics. This is reflected by a thing called rotational inertia. So, what is rotational inertia? It is the resistance force needed to change velocity. A wheel with higher rotational inertia needs more power to actually start moving than the wheel with lower rotational inertia. Now the question is how to keep the rotational inertia of a wheel lower. Well, the answer is in the weight distribution of a wheel in its design. Wheels with more centered weight to the hub results in much lower rotational inertia than the weight distributed at the rim or lip of the wheel.
Another simple way to understand rotational inertia is to think of spinning a weight attached to a string of a couple of inches long. It will be easy to start spinning the weight but what if the string length is increased to 2 feet? Yes, it will be fairly difficult. The same principle applies to the weight distribution distance from the hub.
Effect Of Wheel Weight On Performance
We have already discussed that heavy vehicles are harder to accelerate and decelerate, reducing the wheel weight is the easiest and the most cost-effective way to reduce the ‘unsprung’ weight of the vehicle. There is a lot of physics involved in the impact of this change, but ultimately the suspension becomes more responsive and does its job efficiently.
It is said that adding a single pound of unsprung weight on a drag strip race car has the same effect on performance as adding two or more pounds of sprung weight.
Imagine two Camaros, one installed with small 30 lbs wheels each and the other with bigger 50 lbs wheels each. Let's discuss in detail all the performance indicators in these two cars.
In order to get the Camaro with lighter wheels moving, the engine would have to spin only 30 lbs wheels which would require less power. This would put less strain on the engine and result in more responsive acceleration.
On the other hand, the engine would require more power to move the 50 lbs wheels, putting more strain on the engine, resulting in slower acceleration.
Just like the engine, the brake system would have to work hard to bring the 50 lbs spinning wheels to a halt. More weight means more moment of inertia from a spinning wheel and hence, more time to bring the spinning wheels to a complete stop. This will increase the stopping distance and wear the brake pads fastest than the lighter 30 lbs wheels.
Cornering & Ride
It is easy to experience the dramatic effect of heavy wheels while making a turn or hitting a pothole or a bump. Let’s say you are driving down the road and hit a bump. The bump reacted with a 2g force. If we talk about a 30 lbs wheel, the wheel will experience a 60 lbs force in the Z-axis. But a 50 lbs wheel will experience a 100 lbs force in the Z-axis. This force is supposed to be absorbed by the tire, wheels, springs, and suspension system. The heavy wheel would exert more force on the suspension and hence, the passenger would feel a bigger bump. Over time, your suspension system will experience more wear.
It won’t be a straightforward answer if we say that heavy wheels reduce fuel economy. The answer depends on the driving style. If a vehicle is usually driven on a freeway then heavy wheels would not affect the fuel economy much but if the vehicle is driven in the city with frequent stops then the heavy wheels would impact the fuel economy. This is because in city driving the engine is frequently applying more power to get the heavy wheels moving from a stop position.
If you install lightweight wheels on a hybrid or other efficient vehicle, you will notice a significant improvement in performance. If we combine lightweight wheels with energy-efficient tires that will lower the rolling resistance and would improve the fuel efficiency even further.
Now whenever you are out shopping for new wheels, you know what to look for to get the best performance from your vehicle.