Are Alloy Wheels More Fuel Efficient?

This is actually a far less straightforward answer than it might at first seem.

 Yes, of course, alloys are far lighter than steels, meaning a lighter vehicle and even a lower unsprung weight, offering better handling and thus in theory at least, less consumption. However, this potentially only works if you are replacing like for like. If you were to replace your steel originals with larger alloy rims, any weight saving you thought you might be achieving will actually be negated by the increased wheel dimensions.

But aside from this, where fuel consumption is really impacted is in the aerodynamics of the vehicle. The difference in weight of the wheels between alloy and steel really is a small contributor in comparison.

And what steel wheels will give you, in general, is a good flat surface for the air to pass across, whilst the car is in motion. Spoked alloy designs, being what they are, tend to really break up the airflow, noticeably increasing the drag and therefore the fuel consumption, although they do help dissipate the heat generated under braking more efficiently than their steel counterpart.

When you realise that the wheels are on four key corners of the car, this greatly increased turbulence is having quite an effect on your car’s aerodynamics.

For drag to be at a minimum, the car needs to pass through the air with the least disruption. If you consider any vehicles renowned for their speed, you will notice flat, or even covered wheels, to help integrate them into the vehicles overall smooth design. The air needs to ‘stick’ to the car and not be broken up as it flows across the surface.

Newer designs concerned with fuel efficiency have certainly embraced this knowledge, dispensing with appearance for the sake of great fuel mileage figures. Ideally, you need to cover not only the rear wheels but the front ones too, though this provides its own set of additional problems with steering and such. The greatest issue here though is simply appearance; no one seems to like this look much at all, or it would have hit general manufacturing procedure much more widely than it has.

Additionally, the narrower the wheel, the better, allowing it to slice through the atmosphere and not create air resistance to build-up too much in front of the tyre. Another area for serious consideration is low-resistance tyres, running at high pressures.

So, ideally, you want a smooth-sided, narrow wheel with no holes in, which at the same time allows the brakes enough air to cool efficiently, under heavy braking.

In motorsport, the weight saving and heat dissipation offered by mags is a no brainer. Especially that of the more expensive magnesium wheels, which are even lighter than aluminum alloy rims and cost is no object. However, they also need great torsional strength and unrestricted access to the wheel nuts. With land speed records or drag racing however, you can see where the priorities lie.

So, to answer the question, if you replace like for like, size for size, then you may well see a slight reduction in fuel consumption, you may not. However, for any kind of noticeable improvement, something a little more radical is needed.