Working with various wheel sizes in your career, you may have clients ask questions about why drivers would choose larger or smaller wheels for their cars, or why companies release certain wheel sizes rather than others.
The more knowledge you have about these choices, the more dependable and trustworthy you will be when clients have casual questions about their vehicles. This is also fun information to have when working on a vintage project car or browsing new models at a car show. Read on for some of the ways that the size of wheels can affect a car.
In an Automotive Career, Wheel Size Hints at Performance Characteristics
When the wheel diameter is increased, it’s more difficult for the same level of torque to create driving force, and the added tire area in contact with the ground creates rolling resistance. This results in a decreased acceleration rate (assuming that all other parts of the car, like the engine and gears, are kept constant).
Corners will feel different with large wheels vs. small ones. Since larger wheels have more width, and have the aforementioned increase in surface area that is in contact with the ground, the tires are better able to grip the road. Since the car is better able to grip corners, body roll can increase. To safeguard from accidents relating to body roll, it’s helpful to stiffen the suspension and provide extra stability against rolling. In an automotive career, you may see a setup like this in some of the cars you work on.
Smaller diameter wheels are more responsive to acute adjustments, so drivers can handle steering more concisely and effectively. The smaller wheels won’t push as far within changes in direction, whereas big wheels will push farther within turns and be unable to make changes as accurately and efficiently.
The Driver and Passenger Experience Changes with Wheel Size
When changing the size of wheels, the experience for passengers riding in the vehicle will be altered. Noise, Vibration and Harshness (NVH) refers to the noise and vibration that occurs in vehicles. Small wheels cause less harsh vibrations and are much quieter than larger ones. This can also be affected, however, by the type and brand of tire that is chosen.
The sidewall, as you may know already from training to become a mechanic, is the part of the tire that exists between the outside and inside diameters, between where the tire hits the ground and where it touches the wheel. The more sidewall a tire has, the better the cushioning effect. Larger wheels, of 18-, 19-, and 20-inch diameters, have much narrower sidewalls. Smaller wheels have more sidewall and can cushion and absorb bumps and potholes better, which not only improves the comfort level of passengers but also helps preserve the integrity of the tires and wheels, leading to less of a need for replacements.
For handling high speeds on highways, larger wheels get some points. The better stopping power and stability of larger wheels can be comforting during fast, straight line driving. However, since they don’t turn as well as smaller wheels, there is a trade-off in terms of agility.
You’ll Notice Manufacturers’ Choices When You Become a Mechanic
As mentioned, the larger the wheels of a car, the more difficult it is for the engine to rotate the wheels. This burns more fuel and in order to match a target fuel economy, manufacturers will take wheel size into account. If a car is created primarily as a performance vehicle and the most important thing is handling, traction is key for turning corners and coming out of stops. In this case, fuel economy will not be as much of a concern and larger tires will be a good fit.
Looking cool is still important to a lot of drivers, so it’s something manufacturers care about too. Some drivers simply like the look of larger wheels, more filled-in arches, and a lower, more hunkered-down look. The profile of these cars will look more similar to a race car and have a sportier vibe. It’s not uncommon for wheel size to be primarily about style.
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