The Connection Between Wheel Weight & Performance Wheels

When people look for aftermarket performance wheels or high performance wheels, the first thing they look for is style.  And the different styles help makes the vehicle personal to the owner.  After style, they consider .the not-so-cool things like wheel diameter, width and offset that are right for the vehicle and appropriate for the desired tire size.

Styles evolve, but there are some designs that are timeless and classic, including the basic five-spoke, six-spoke and cross-spoke designs.  And because the look of these classic designs came from racing wheels, this particular form comes from function. What this means is that this basic design allows the engineer to balance style, strength and weight.

There are, however, fashion wheels which, change with whatever happens to be popular at the time.  In this case function comes from fashion.  In this case, the designer (not engineer), makes style the priority over weight.

And because most of fashion wheels aren’t meant to last long, the design the engineer produces emphasizes the ability to manufacture wheels economically in small volumes. Unfortunately, this usually doesn’t include the most recent high tech manufacturing methods.

But the connection between wheel weight and to the vehicle's overall ride, performance, and feel is not so obvious to everybody. That’s why so many new vehicles have replaced steel wheels with cast aluminum alloy wheels.

Since the original mag (magnesium alloy) wheels were developed to reduce wheel weight on the race cars of the 1950s, lightweight wheels, they have been used to enhance vehicle performance in almost all forms of racing. And although the name mag is still used today, most magnesium performance alloy wheels are too fragile to use for daily driving.

The most common uses nowadays for magnesium alloy performance wheels are on Champ Cars, Indy, Formula 1 and GT cars where they can be tested between events. Modern racing mag wheels often use a high tech manufacturing process and special magnesium alloys to reduce the weight while they retain the ability to handle the high loads.

And for the rest of us, wheel manufacturers have also developed lightweight aluminum alloy wheels that are good enough for the street.

The total weight of a vehicle is the sum of all of its parts that affects its ability to accelerate, brake and corner. If you reduce the vehicle’s total weight, it will enhance the vehicle's performance because less weight needs to be controlled requiring less energy.

Unsprung weight is the weight under the springs which moves up and down as the vehicle rides over uneven roads and leans in the corners. If you reduce unsprung weight, it lets the springs and shock absorbers to be more effective in controlling the suspension's movement.

A vehicle's rotational weigh is the weight of all its spinning parts, including everything in the vehicle's driveline from the engine's crankshaft to its wheels and tires. Rotational weight affects the energy required to change speed when the vehicle speeds up or brakes. And, if you reduce the weight of any of these rotating components, it will enhance the vehicle's performance because less energy is needed to increase or decrease their speed.

So that we could get a better idea about the connection between wheel weight and a vehicle’s performance performance, comfort and feel, a respected tire distributor conducted a Ride & Drive that compared a BMW 3-Series that was equipped with its Original Equipment (16") wheels and tires in order to establish a comfort and handling baseline, to two other BMW 3-Seriesw vehicles.

The second BMW 3-Series vehicle was equipped with Plus One (17") wheels & tires using lightweight aluminum alloy wheels. And the third BMW 3-Series was equipped with the same size Plus One application but with heavyweight aluminum performance alloy wheels.

Original Equipment (OE) BMW 3-Series Alloy Wheels and Tires

Equipment: 16" x 7" sized OE BMW wheels and 205/55R16 91H-sized Michelin Energy MXV4 Plus tires

The aluminum alloy wheels features cross-spoke styling and weigh an estimated 20.5 pounds each.

The Original Equipment on our BMW 3-SeriesEnergy MXV4 Plus are Grand Touring tires.  These tires combine some of the looks and handling of a performance tire with a standard passenger tire's longer life and more comfortable ride.

The Energy MXV4 Plus incorporates an advanced version of Michelin's Radial XSE Technology.  This technology consists of a Smart Tread Compound, Optimized Casing Shape, and Optimized Mass Distribution. The OE Michelin Energy MXV4 Plus tires weigh 22.5 pounds each

The combined weight of the Original Equipment Energy MXV4 Plus tires mounted on the BMW performance alloy wheels is 42.5 pounds.

The OE BMW alloy wheels and Energy MXV4 Plus tires provided a good ride, had low noise, and had a real world handling and steering feel on the road. The car felt balanced and had a relatively light steering feel that felt appropriate for the car.

This combination of real world ride, noise and handling qualities were exactly what BMW engineers wanted for their 3-Series sedan. This combination was rated as responsive and predictable and at the same time provided good braking, cornering traction and handling.

But, as we expected, this car had the slowest lap times of the three combinations tested.

Plus Size Wheels & Tires Using Lightweight Wheels

Equipment: SSR Semi-Solid Forged 17" x 8" alloy wheels fitted with 245/45ZR17-sized Pirelli P Zero Asimmetrico tires

The SSR aluminum performance alloy wheels used in this test feature five-spoke styling and a unique manufacturing process called Semi-Solid Forging (SSF).  

Low porosity and lightweight, SSF produced wheels are made using a process originally developed for aircraft and automotive parts which require high strength. 

They use a special aluminum alloy that is heated until it has about the consistency of warm butter, and then it is forced into the mold under high pressure.

The result of this is a strong, lightweight wheel that offers many of the traits of traditionally-forged wheels, but it costs less to manufacture and is more affordable.

 The lightweight 17" x 8" SSR aluminum alloy wheels on our 3-Series test car only weighs 17 pounds each.

The tires used in this test were Pirelli P Zero Asimmetrico Max Performance tires.  These tires feature a lightweight construction and an asymmetric tread design that was developed to maximize the tire's ability to put the power down.  This is whether accelerating, braking or cornering.

Also, the P Zero Asimmetrico tread compound enhances wet traction and reduces rolling resistance by combining traditional carbon black with a special blend of silica and synthetic polymers.  The P Zero Asimmetrico is used as Original Equipment on many performance vehicles, including the BMW E36 M3.

The weight of each 245/45ZR17-sized Pirelli P Zero Asimmetrico tires is 21.5 pounds.

The combined weight t of the Plus One-sized P Zero Asimmetrico tires mounted on the SSR Integral alloy wheel is 38.5 pound Tire & Wheel Package.

This combination had good steering feel and responsiveness on the road, but it generated a small increase in ride harshness on bumpy roads. On the track, however, this combination had good feel, feedback and responsiveness. It had a feeling lightness and nimbleness, and seemed ready to transform the driver's input into performance.

Out of all 3 cars tested, this car had the fastest lap times.

Plus Size Wheels & Tires Using Heavyweight Wheels

Equipment: 17" x 8" alloy wheels fitted with 245/45ZR17-sized Pirelli P Zero Asimmetrico tires

The heavyweight aluminum alloy wheels that were used in this test were selected because they were designed to emphasize a trendy fashion style and NOT overall weight.

The weight of these heavyweight aluminum alloy wheels on this BMW test car is 27 pounds each (ten pounds heavier per wheel than the lightweight wheels).

The combined weight of the Plus One-sized P Zero Asimmetrico tires mounted on the heavyweight alloy wheel is 48.5 pounds. This is about 7 pounds heavier than the stock combination.

This combination was only praised for its ride quality on the road. The heavyweight wheel was reluctant to be moved as the vehicle rode over expansion joints, patches and potholes.  They actually damped the impact harshness transmitted to the suspension, and forced the tires to absorb more of the jolt.

When it came to steering feel and responsiveness, however, heavyweight wheels made the tires not as communicative and responsive when traveling at highway speeds.

On the track, this combination had nothing to be praised about. It had a feeling of heaviness and lethargy.  And it actually reduced the feedback the tires normally transmit to the driver, thus making the vehicle more difficult to drive at the limit. It was for the driver to know how much input was required.  Therefore, it reduced the vehicle's ability to transform the driver's input into performance.

Many of our team members made the analogy of jogging with ankle weights or hiking with field boots. You only notice the difference when you take them off.  The car equipped with the heavyweight alloy wheels and Pirelli P Zero Asimmetrico tires had good handling but couldn't match the performance of the lightweight combination.

Its lap times were in the middle of the other two combinations tested.

We expected to feel the gyroscopic effects of wheel weight at highway speeds but were rather surprised at how they influenced the car's feel at the lower speeds on our performance test track drive.

In addition, we realized how the impact of heavyweight wheels increased at top speeds on a race track so it’s obvious now why professional race teams spend thousands of dollars for wheels that minimize weight while retaining strength.

Lastly, we monitored fuel economy.  We covered just over 350 miles.  The three vehicles’ average speeds were virtually identical (all within 3/10 of 1 mph).

At that time the BMW 3-Series that was equipped with the Original Equipment Grand Touring Michelin Energy MXV4 Plus low rolling resistance tires averaged 22.8 mpg. The vehicle equipped with the Plus Size Pirelli P Zero tires on lightweight wheels averaged 21.5 mpg.  And the Plus Size Pirelli P Zero tires on heavyweight wheels averaged 21.1 mpg.

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