For car upgrades, one of the first and easiest ways to think of is to change the hub, but what effect will the replacement of the hub have on the speed increase and overall performance of the vehicle?
You may often see some Volkswagen Golfs and Audi A4s with more ground clearance than normal, and the wheels they are fitted with look a lot larger than normal. To be honest, since the original wheels that most manufacturers give cars as standard are really flat, in order to improve the overall visual impact of the car body, many enthusiasts are very keen to replace large-sized wheels to make them look better. Aggressive, which is completely understandable. However, does the replacement of the big wheels affect the original performance of the car? Is there a certain degree of improvement in acceleration performance from 0-60 mph in particular?
First, let’s briefly understand the fundamentals of wheel dynamics. To make the wheel turn, a torque is needed to drive the axle, and we can calculate the corresponding torque using the radius of the wheel and the tangential force of the wheel.
If the torque value is treated as a constant (assuming a steady torque from the car engine), then the wheel radius changes and the driving force from the wheels changes accordingly.
Let’s take the 1.6-litre Volkswagen Goft GTI fitted with 15 inch wheels as an example, which produces a maximum torque output of 350 Nm. Assuming an even distribution between the two wheels (175 Nm each) and disregarding the effect of transmission efficiency, all power goes to the wheels, the calculated driving force is around 460N. When the wheel diameter is increased to 19 inches, the driving force is reduced to 360 N. According to Newton’s second law, the force acting on an object is equal to its mass times its acceleration. Therefore, increasing the wheel size will reduce the driving force transmitted to the wheels, ultimately resulting in a reduction in the car’s acceleration. The above assumes that all other components such as engine, driveshafts, gears and differentials are still using original parts designed for the original factory standard wheel size.
To achieve the same acceleration with increased wheel size, the engine has to work harder to turn the wheels, so fuel economy is bound to suffer.
Car and Driver magazine once ran an interesting test to prove how much wheel size affects the acceleration of a Volkswagen Golf. The car was tested for 0-60 mph times with different wheel sizes, and with 15 inch wheels, it took just 7.6 seconds. When the wheels are increased to 19 inch wheels, the acceleration time increases to 7.9 seconds. Tests from 0-100 mph yielded the same results, establishing that larger wheels would reduce the car’s acceleration performance.
Since the speedometer and gearing of the car are designed according to the standard tire diameter, the wheel size is increased, the thickness of the tire must be reduced to maintain the same overall diameter, and the car can be exempted from re-tuning. This also means that the sidewall of the tire must be stronger to withstand the lateral forces of production during cornering, so the application of flat tires reduces driving comfort.
Also, increasing the diameter of the wheel hub usually increases the width, which increases the contact surface between the tire and the road to improve grip, but the increase in friction makes it harder for the car to drive through corners and the body rolls The degree will be greatly increased, so it is necessary to strengthen the suspension to maintain the stability of the car.
Also, the handling of the car will vary with wheel size, smaller diameter hubs will allow for cleaner handling as the wheel covers less distance per revolution, while larger, wider (heavier) The wheels have the potential to cause understeer, making maneuvering difficult.
So, do you want to pursue „beauty” or „performance” when it comes to replacing large-sized wheels?