Much more so when combined with a heavy set of alloy rims or steelies.

It’s not just fuel economy. It’s also tyre wear, comfort, and drivability.

But why?

Unsprung Weight – Why heavy wheels are worse than a heavy load

Without getting bogged down in science, a car has sprung weight (everything on top of the suspension), and unsprung weight which includes your wheels, tyres, and part of your suspension.

Imagine you have a heavy ball and a bouncy ball.

If you bounce them together you’ll find the bouncy ball has much more energy, whereas the heavier ball will thud and barely bounce.

With the wheels and tyres on your car it’s the same effect, except the bounce is the other way. When you hit a bump in the road this will force your tyres up in the air, losing traction. A lighter wheel and tyre will have less unsprung weight, more energy, and return to the road’s surface much more quickly.

The higher workload required of a heavy wheel and tyre will reduce the effectiveness of your suspension, drivability of your car, and increase fuel consumption.

This is the reason car enthusiasts in the know opt for light wheels such as OZ Racing rather than bling alloys designed for look and not performance.

Rotational Mass – The numerous problems of heavy rotations

The affect of unsprung weight is more noticeable on fuel economy, but the affects of rotational mass come a close second.

Rotational mass refers to any component which rotates with the wheel assembly – namely the wheel itself, tyre, and lug nuts. The heavier the components, the more energy will be needed to accelerate and decelerate. This energy comes from your engine (or battery if you have a fancy modern EV), and the greater load on your engine affects fuel efficiency.

Also, the further the mass from the centre of the wheel the more inertia it will cause, so a heavy tyre can cause more fuel consumption than a heavy wheel, and make your car less performant to boot.

Research has shown the affect of rotational mass on fuel economy can be small, but will have a more significant impact in city start-stop-start-stop driving.

It will also affect your time around the Nürburgring if you ever take your V8 Commodore to Germany.

Final thoughts on tyre weight and fuel economy

Whether you refer to fuel economy as mpg or litres per 100 kilometers (L/100 km) like we do in Australia, a heavy tyre or wheel will have a negative affect on fuel economy and drivability as well.

There are other factors at play as well, such as choice of tyre, tyre design, tread pattern, and inflation pressure. Generally for you as a driver a decent mid-range or premium tyre won’t cause any noticeable negative affects on fuel economy, and there are much bigger savings to be had if you read our guide on finding real discounts on tyres.

Wheels and tyres are just one of many variables which affect your car’s overall fuel economy, and if you want to get really pedantic, some flattening your rear seats when not in use will also increase fuel economy (true in theory, believe it or not!)