The Influence of Wheel Weight on Performance Wheels

Style is the first thing people look for in aftermarket performance wheels or high performance wheels. The different styles help give the vehicle a personal touch  After style is considered, then .they look for the  not-so-cool things like wheel diameter, width and offset that are right for the vehicle and appropriate for the desired tire size.

Although styles are always evolving, there are some designs that are considered timeless and classic.  These classic designs include the basic five-spoke, six-spoke and cross-spoke designs.

But this particular form comes from function because the look of these classic designs came from racing wheels. What that all means is that this basic design allows the engineer to balance style, strength and weight.

On the opposite end are fashion wheels.  Fashion wheels change with whatever happens to be popular at the time.  In the case of fashion wheels, function comes from fashion.   Style takes priority over weight.

For fashion wheels the engineer emphasizes the ability to manufacture wheels economically in small because most of fashion wheels aren’t meant to last long. And unfortunately, they are usually not manufactured with the most recent high tech manufacturing methods.

The thing is that the connection between wheel weight and to the vehicle's overall ride, performance, and feel is not obvious to everybody. That’s the reason why so many new vehicles use cast aluminum alloy wheels instead of steel wheels.

From the race track to the road…

Magnesium alloy (mag) wheels have been used to enhance vehicle performance in almost all forms of racing since they were developed to reduce wheel weight on the race cars of the 1950s, lightweight wheels. But even though they still use the name “mag” today, most magnesium performance alloy wheels are too fragile to use for daily driving.

Champ Cars, Indy, Formula 1 and GT cars use magnesium alloy wheels nowadays and are tested between events. And to reduce the weight while they retain the ability to handle the high loads, modern racing mag wheels often use a high tech manufacturing process and special magnesium alloys.

Let’s not forget the rest of us though.  For us, wheel manufacturers have developed lightweight aluminum alloy wheels that are good enough for the street.

Different vehicle weights

l       Total weight- the sum of all of its parts that affects its ability to accelerate, brake and corner. The vehicle's performance will be enhanced if you reduce the vehicle’s total weight because less weight needs to be controlled requiring less energy.

l       Unsprung weight-the weight under the springs which moves up and down as the vehicle rides over uneven roads and leans in the corners.  The springs and shock absorbers will be more effective in controlling the suspension's movement if you reduce unsprung weight.

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

Testing the influence of wheel weight on performance

We decided to get a better idea about the influence of wheel weight on a vehicle’s performance performance, comfort and feel.  So a respected tire distributor conducted a Ride & Drive that compared 3 vehicles.  The first was a BMW 3-Series 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 was a  BMW 3-Series vehicle equipped with Plus One (17") wheels & tires using lightweight aluminum alloy wheels, and the third was BMW 3-Series equipped with the same size Plus One application but with heavyweight aluminum performance alloy wheels.

Car #1: 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. Each aluminum alloy wheel featured cross-spoke styling and weighed an estimated 20.5 pounds each.

Energy MXV4 Plus Grand Touring tires were the Original Equipment on the BMW 3-Series.  These tires are famous for combining a standard passenger tire's longer life and more comfortable ride with the looks and feel of a performance tire.

The Energy MXV4 Plus is an advanced version of Michelin's Radial XSE Technology.  It consists of a Smart Tread Compound, Optimized Casing Shape, and Optimized Mass Distribution.

 The OE Michelin Energy MXV4 Plus tires each weigh 22.5 pounds.

Combined Weight: The tire and wheel combination of the Original Equipment Energy MXV4 Plus tires mounted on the BMW performance alloy wheels weighed 42.5 pounds.

Road Test: The OE BMW alloy wheels and Energy MXV4 Plus tires was noted for its good ride, low noise, and a real world handling and steering. The car had a relatively light steering feel that felt appropriate for the car and felt balanced.

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

Lap Time: This car had the slowest lap times of the three combinations tested, as we expected.

Car #2 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.  They are low porosity and lightweight.

They were made with a manufacturing process called Semi-Solid Forging (SSF) that was originally developed for aircraft and automotive parts which require high strength.

The way this works is that they use a special aluminum alloy that is heated to the point where it was a warm butter consistency, and then it is forced into the mold under high pressure. This results in a strong, lightweight wheel, which offers many of the traits of traditionally-forged wheels but at a much cheaper cost. .

The lightweight 17" x 8" SSR aluminum alloy wheels only weigh 17 pounds each.

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

Also, the P Zero Asimmetrico tread compound combines traditional carbon black with a special blend of silica and synthetic polymers, thus enhancing wet traction and reduces rolling resistance.  In fact, the P Zero Asimmetrico is used as Original Equipment on many performance vehicles—including the BMW E36 M3.

These tires weigh 21.5 pounds.

Combined Weight: The combination of the Plus One-sized P Zero Asimmetrico tires mounted on the SSR Integral alloy wheel weighs 38.5 pounds.

Road Test: This combination had good steering feel and responsiveness but was a little harsher on bumpy roads.

Track Test: This combination had good feel, feedback, and responsiveness. It felt light, nimble, and seemed ready to transform the driver's input into performance.

Lap Times: This car had the fastest lap times out of all the cars tested.

Car #3 Plus Size Wheels & Tires Using Heavyweight Wheels

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

We selected the heavyweight aluminum alloy wheels that were used in this test because they were designed for style, NOT overall weight.

The tires weighed 27 pounds each--ten pounds heavier per wheel than the lightweight wheels.

Combined Weight: The combination of the Plus One-sized P Zero Asimmetrico tires mounted on the heavyweight alloy wheel weighed 48.5 pound, about 7 pounds heavier than the stock combination.

Road Test: The only good thing about this combination was its ride quality. It was hard to move the heavyweight wheel as the vehicle rode over expansion joints, patches and potholes.  In fact, they actually damped the harshness of impact transmitted to the suspension, making the tires to absorb more of the jolt.

When traveling at highway speeds, however, heavyweight wheels made the tires not as communicative and responsive.

Track Test: This combination was praised for nothing. It made the car feel heavy and lethargic; actually reducing the feedback the tires normally transmit to the driver.  Thus they made the vehicle more difficult to drive at the limit. It was up to the driver to figure out how much input was required.  Therefore, the vehicle's ability to transform the driver's input into performance was reduced.

An analogy for this would be jogging with ankle weights or hiking with field boots. You don’t notice the difference until you take them off.  The car equipped with the heavyweight alloy wheels and Pirelli P Zero Asimmetrico tires handled well but was not able to match the performance of the lightweight combination.

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

Also the impact of heavyweight wheels increased at top speeds on a race track.  So now we know why professional race teams spend thousands of dollars for wheels that minimize weight while retaining strength.

Lap Times: Its lap times were between the other two combinations tested.

Fuel Economy Comparison of all 3 cars

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

Here are the results:

Car #1 (Original Equipment Grand Touring Michelin Energy MXV4 Plus low rolling resistance tires): 22.8 mpg

Car #2. (Plus Size Pirelli P Zero tires on lightweight wheels): 21.5 mpg.

Car #3 (Plus Size Pirelli P Zero tires on heavyweight wheels): 21.1 mpg.

article courteousy Tire Rack