Smarter, lighter, more effective: A time-old technology that has been servicing humankind couldn’t possibly be perfected any further. However, with the advent of newer materials and technology, can wheels compete with the road condition?
Human progress can be charted right up to the invention of the wheel. Since then it has been the paragon of all the things we can achieve. Imagining a car without wheels is just impossible. Simply dragging a frame as huge as a car (or even a cart, for which the wheel was originally made) on the ground will cause friction to slow down the frame, not to mention the amount of effort and power that would be wasted in that endeavour. For this reason, wheels were fitted to various applications--- and even modified for gears and winches--- in order to reduce the amount of friction that would sap out the power from the frame’s mobility.
This is of course not to say that there isn’t any friction between the wheel and the ground. Friction is an important aspect of keeping the vehicle steady and not letting it just roll.
Of course, while the basic shape and function of the wheel hasn’t changed much, it has definitely been improved upon by the auto wheel manufacturers. The functioning of a wheel in a car is slightly different as there has to be an application of rotational force to produce a linear movement. For this purpose, there are different materials used to make the wheel lighter in weight, which overall contributes to the lightweighting trend and can also increase the speed of the vehicle.
Steel vs Alloy
One of the newer trends that have been gripping wheel manufacturers is the usage of alloy wheels, or colloquially known as aluminium wheels. Traditionally all the wheels manufactured are some grade of steel wheels. Nothing beats the strength of steel wheels and they are used in almost every application: cars, SUVs, bikes, motorcycles, scooters etc. Heavier grades of steel wheels are used in construction equipment or all types of commercial vehicles (CVs). Steel wheels are also a form of alloy made out of carbon and iron. However, terminology wise, the name alloy wheels refer only to steel’s lightweight counterparts.
Alloy wheels are generally made out of alloys of nickel, magnesium and aluminium individually. A combination of aluminium and magnesium alloy wheels are also quite popular. The trend of alloy or aluminium wheels trickled down from the world of motorsports where lightweighting even by a few milligrams makes all the difference in performance. These wheels are not only strong, but they also carry a certain aesthetic appeal due how low the cost of tooling is when it comes to aluminium. Aluminium wheels are easily malleable and can be designed in different ways. This freedom with customisation allows for cars to have a distinct look as per the owner’s specifications. Simply put, alloy wheels offer the strength of steel wheels but are lighter in weight.
The downside of aluminium wheels, however, is that they are not cost-effective and hence a buyer might purchase it only if aesthetics were the main buying factor to consider. Alloy wheels are also more costly to produce than steel wheels; and despite having the advantage of malleability is also extremely vulnerable to damage unlike steel. Nickel is often added to the aluminium to make it more pliable which can cause the wheel to bend more easily under road impact and can even crack if the road conditions are not good. In addition to all of this, caring for alloy wheels can be difficult considering how susceptible they are to corrosion from acid cleaners or even plain old salt water.
Another reason why aluminium wheels don’t occupy a majority market share is the constant lightweighting of steel. As most parts of a vehicle are made of steel, there is a conscious effort towards producing lighter grades of steel. The weight difference between light grade steel and alloy wheels is barely noticeable for an everyday driver. This difference counts for a lot only on the race track. If aesthetics are not a major concern, then the utilitarian steel wheels are sufficient for most customers. Adding to this, steel wheels are generally sturdier. While alloy wheels are strong, steel wheels lack their brittleness. Indian road conditions in particular are easily sustained by steel wheels. Even if there is a chance of any damage, the wheel can easily be beaten back into shape by a hammer and there is no chance of it cracking or breaking either. This is why aluminium wheels are not as common on all passenger cars or don’t occupy majority market share. Even when not on the track, alloy wheels are often found on passenger cars or on light commercial vehicles at most. Heavy commercial vehicle and construction equipment manufacturers still favour steel wheels due to the aforementioned properties.
A rarer, more expensive kind of wheel is one made out of carbon fibre. These wheels are commonly used in bicycle racing and have only recently made their way into the passenger car segment. However, the only two known car companies to use them on exclusive models are Porsche and Ford. The Porsche 911 Turbo S Exclusive Series uses a particular technique for its carbon fibre wheels. The sports car’s entire wheel is made out of carbon fibre reinforced polymer (CFRP), of which the rim is made of braided carbon fibre while the centre is made of carbon fibre fabric. The wheel rim is then braided onto the centre and then goes through a hardening process under high pressure and high temperatures. The finished wheel undergoes a long cooling process, after which it is protected by a layer of clear lacquer. This complicated process is used only by Porsche on its Turbo S Exclusive Series, which the company claims offers 20 per cent lightweighting as compared to alloy wheels. In addition to that the braided carbon fibre wheels are sturdier and more rigid as compared to other processes of making carbon fibre wheels.
Another important aspect behind wheels is the power that is used to drive them and how it is supplied to them. For smoother mobility, friction needs to be reduced anywhere in a vehicle. This also contributes to fuel-efficiency and saves power wastage.
For smoother operations wheels are placed around an axle that connects one side of the vehicle’s wheels to the other side. An axle can be considered as the muscle of the car where it transfers the power and the torque from the engine to the wheels. Axles are also used for steering the vehicle, driving and even braking. The transfer of power and torque from the engine means that all the weight of the vehicle, cargo or passengers falls on the axles because of which it needs to be robust in build. The forces involved in driving and accelerating also need to be withstood by the axle.
In certain types of drives the engine power or transmission flows only to one of the axle sets or the drive axle. The drive axle is connected directly to the driveshaft which is a rod that extends to the vehicle’s transmission and then connects to engine directly. In case of front wheel drives, the front axle would be the drive axle and the back axle would be termed as the dead axle. The engine itself turns only the front axle. The dead axle is not connected to the engine at all and only turns when the vehicle is in motion, caused by the drive axle. Dead axles are present in vehicles to help support the weight of the car.
However, in bigger vehicles like SUVs, and other vehicles that explore alternative terrains, the dead axle can be given power if the driver chooses to do so. In all wheel drive vehicles, the power transfer to both wheels is permanent. Of course this can cause problems as all wheels don’t require the same amount of power transfers especially while cornering or turning. This is why electronic AWDs are superior to mechanical AWDs. In a mechanical AWD, three different gear boxes will split the engine power between the two wheels of the front or rear axle, and yet another centre differential will split it in between the entire axles themselves.
Today, the power transfer to wheels is much smarter with the involvement of computers and electronic control units (ECUs). The sensors on wheels can detect how much traction is present and the speed of each wheel and an ECU will direct the power to the individual wheel accordingly.
With electrification on the rise and companies like ZF and Bosch providing e-axles or completely electrified powertrain solutions for electric vehicles and hybrid vehicles, the power distribution to each wheel can be controlled more precisely with the help of softwares. In all-electric cars, mechanical transmission is completely eliminated and both axles need not be connected to the engine either. In the future, electric motor power would alone power everything including wheels.