How Does Wheel Size Affect Performance?

Nothing expresses ownership the way personalization does. Aftermarket wheels are popular because they are among the easiest upgrades available to car owners. However, poor wheel choice can adversely affect your vehicle’s riding characteristics.

Your vehicle’s wheel size alters key riding characteristics such as comfort, acceleration, and fuel economy. Many shops can help you find the right wheel size. However, understanding how tire and wheel size affect vehicle performance will allow you to identify the parameters for tasteful wheel choices that don’t compromise your vehicle’s performance.

Understanding Wheel Dynamics

The fundamental idea of an internal combustion engine is that it converts heat energy into kinetic energy. The powertrain — which includes the engine, transmission, driveshaft, axles, and differential — transfers power from the engine to the wheels, causing the vehicle to move. Altering any of these components can affect the careful balance of your vehicle’s mechanical characteristics.

Torque and Driving Force

Torque refers to the measurement of force applied in a rotational motion. It relates to the maximum twisting force generated by an engine. This twisting force is responsible for the horizontal force needed to move your vehicle. Torque is the primary factor that affects acceleration. The greater the torque, the quicker the acceleration.

Driving force refers to the force responsible for setting an object into motion. The static friction between the tires and the ground enables the vehicle to move forward. Static friction is also present between lugnuts, the wheel, and the axle. This is why vehicles struggle to accelerate or brake on icy roads and predicate the need for special tires, which increase friction between tires and snow.

For a car to move forward, the tires must “grip” the road for the car to “pull” itself forward with the rotational force from the engine. Friction between the road and tires also allows brake force to affect the vehicle’s motion. The right amount of friction is key to optimal performance.

• Torque refers to the maximum rotational force your engine can generate. The greater the torque, the quicker the acceleration.
• Without friction, there can be no driving force.
• Too much friction increases the force required to move your vehicle.

Wheel Radius and Driving Force

The first thing to understand is that wheel radius does not affect torque. Instead, it increases the force needed to move the vehicle. This is primarily because having larger wheels translates to greater friction and weight.

• Increasing the wheel radius decreases the driving force from your wheels.
• Increased wheel radius increases traction, which enhances cornering, handling, and braking.

The Effect of Wheel Size on Performance

Now that we understand the basic dynamics between torque, wheel radius, and driving force, let’s delve into how they affect different facets of vehicle performance.

Acceleration

Installing larger wheels increases your vehicle weight. The added weight decreases acceleration because your engine (assuming it’s left unaltered) will have to work harder to move your vehicle. This also affects how power is transferred throughout the subsystems of your powertrain.

The gear ratios and the transmission are optimized to deliver acceleration based on stock wheels and their weight. Altering your wheel size negates the careful balance of these optimizations between gear ratios and your transmission.

Powertrain Efficiency

The added weight and bigger size of larger wheels also yield a higher rolling resistance. The energy transferred from your engine to your wheels diminishes because of the greater resistance from your wheels.

It’s also important to note that gear ratios are precisely tuned to deliver optimal torque at certain speeds based on stock wheel size. Altering your wheel size throws off this careful balance. Larger wheels will cause your transmission to work harder than it needs to, resulting in less force acting on the wheels.

Handling and Stability

While larger wheels can improve traction and cornering performance, their added weight and larger diameter can affect the weight of your steering and its responsiveness. Larger wheels require tremendous effort to steer and can cause your vehicle to understeer.

Larger wheels have an improved contact surface, improving your vehicle’s braking distance and stability as you navigate corners. This makes larger wheels ideal for performance cars, as they require greater stability given the speeds at which they are designed to travel.

Fuel Economy

A larger wheel size causes your powertrain to work harder than it would with your vehicle’s recommended wheel size. Larger wheels have excellent rolling resistance and weight. Larger wheels also tend to come with wider tires, which have a greater surface area and increase friction with the road.

All these factors lead to reduced powertrain efficiency resulting in worse fuel economy because your vehicle has to spend more fuel to get moving.

Riding Comfort

Wheel size affects your vehicle’s riding comfort by impacting specific aspects of the tires you can use. The larger the wheel size, the lower the tire’s sidewall height will need to be. Sidewall height holds a significant influence over how your tire absorbs road imperfections.

Tires with a low sidewall height will often be made from more rigid materials. This strengthened sidewall helps the tire withstand the vehicle’s weight despite a low sidewall height. A stiffer construction leaves little room for flex. This results in a bumpier ride than what you’d get from your vehicle's original wheels.

However, larger wheels come with larger bases, creating better traction that’s suited for wet and sandy roads, as well as for offroading.

Wheel Size Selection Factors to Consider

Choosing a wheel size typically involves three main factors to consider:

• Aesthetics and personal preference
• Vehicle performance
• Practicality

Wheel size significantly affects many core subsystems of your vehicle. This means that there’s a careful balance that car owners need to maintain if they want to get the most out of their vehicles.

Familiarizing yourself with the vital wheel dynamics and how wheel size affects vehicle performance will allow you to make informed decisions. Generally, you’d be better off sticking to the wheel size your car originally came with.

However, if you really want to upsize your wheels, it’s crucial to note that you’ll need to change other aspects to maintain the careful balance your vehicle was designed for. If you’re unsure how to choose a wheel size without compromising vehicle performance and practicality, please visit our skilled technicians at your local Caliber Auto Care..