Since fuel costs started to skyrocket, we have written about a number of ways people with ICE vehicles can save money, including using eco mode, easing off the accelerator as much as possible and stacking discounts. But there’s another way to make your tank go further, and it’s all to do with tyre pressure. According to the RACV, when your tyres are under-inflated, they create more ‘rolling resistance’, meaning you need to accelerate more, which puts pressure on your engine and makes it consume more petrol than it should.

“For every 1psi [pounds per square inch] drop in tyre pressure, fuel efficiency can decrease by up to 0.3 per cent, leading to higher fuel costs over time,” the RACV website states. Does tyre pressure make that much difference to fuel economy? To test tyre-pressure impact on fuel efficiency, I took my 2021 Hyundai Kona for a spin around Melbourne’s north.

My mission was to drive the same loop with my tyres at 30psi as a control, then at 20psi and finally at 40psi, to see the difference in fuel economy for each. Regular readers may recall a similar experiment I did about a month ago, comparing regular driving mode with ECO and Sport modes. Because I had a tried and tested loop encompassing suburban, highway, freeway and (very traffic-heavy) inner-suburban driving from my last trial all mapped out, I figured I shouldn’t mess with a good thing.

This is the loop I drove: As I noted in my previous piece, this was not a perfect, scientific test. However, I think it gave a good indication of how the same car, driven by the same person, on the same route at a similar time of day, would perform with its tyres at different pressures. I don’t have my own air compressor, so I headed to the local servo (which happened to be my loop’s starting point last time) and set my tyres to 30psi.

As stated above, this test was not perfect, and we know that servo gauges are not always 100 per cent accurate. I also noted that it was a relatively warm day for Melbourne in April, and heat can have an impact on tyre pressure. Anyway, for the sake of this experiment – which likely represents many drivers’ actual experiences – I trusted what the servo compressor told me.

Though 30psi is lower than the level my tyres are typically inflated to, my first loop didn’t feel different from a normal drive. Proof of this was my fuel efficiency for that loop – it came in at 5.9 litres per 100 kilometres. Not bad considering my car’s claimed fuel consumption is 6.2L/100km.

Next was the 20psi loop. I was pretty nervous as I let the air out – it took a while and somehow felt like I was doing something my kids would call “a little bit naughty”. Taking off, I could tell straight away this was going to be a different driving experience.

It felt sort of bouncy, and I definitely needed to be more lead-footed to get to – and stay at – the speed limit. Despite the increased pressure on my accelerator, the trip came in at 6.2L/100km. Sure, it wasn’t as good as the 30psi loop, but I did expect it to be quite a bit worse.

Next up, the 40psi test. This was a much nicer drive – even if it was a tiny bit stiffer on turns. My efficiency quickly made it to 5L/100km, and it stayed there through the freeway and inner-city section of the drive.

The last stretch of my loop has a few inclines, so I did have to give it a bit of throttle through that section. This meant my final efficiency came in at 5.5L/100km. Still, that’s almost 7 per cent better than the 30psi and 11 per cent better than the 20psi.

Using my car’s tank capacity of 50L, current average petrol price in Melbourne and the average number of kilometres Melburnians drive each week, the chart below estimates the difference in weekly petrol costs for each tyre pressure. It’s not an insignificant difference, and if you added it up over a year, it would be a saving of about $77 between the 20psi and 30psi examples, $128 between 30psi and 40psi, and $205 between 20psi and 40psi. Now, we’re not suggesting that 40psi is right for every car, and in fact, my car’s recommended tyre pressure is between 33 and 36psi depending on its load.

However, this experiment highlights that under-inflated tyres can adversely impact the amount of petrol your car uses. And, of course, there are other costs and safety issues that can occur if your tyre pressure is not at the recommended PSI, so it is imperative you check it regularly. If you have any concerns about your tyres, get them looked at by a professional.