Which car rusts the worst? The data is in and it’s eye-popping.

Gone are the days when a new car would start oxidising before your eyes as soon as it left a dealer forecourt, but if you're shopping for a used car, it helps to know which will rust quickest.

We've had plenty of anecdotal evidence down the years of cars that bought cheap Russian steel or which skimped on rustproofing, or even which sat awaiting deliveries up to their axles in water, but we've never had an absolutely bulletproof and unarguable data set. Until now.

British company PlateInsight has analysed the results of 3,142,385 roadworthy tests in order to bring you the facts about which cars were failing the MOT (Ministry of Transport) tests on corrosion-based issues. Overall, it assessed over 261 million data points.

Fortunately, almost all of the noteworthy cars are also sold in Australia, so the data translates fairly well.

What's more, the gulf between the best and worst performers is eye-popping. The 2011 Suzuki SX4 diesel win the dubious honour of metal-moth champion, with corrosion-related defects evident in over 71 per cent of MOT tests.

2011 Suzuki SX4 Crossover S AWD Review

At the other extreme, the 2019 Ford Fiesta scored a barely-there 0.18% defect rate. So while one of these cars will have you checking out your local TAFE for welding classes, the other seems about as impervious to the effects of salty water as a Phillip Island penguin.

PalteInsight has rather helpfully ranked the 20 rustiest cars and the 20 most corrosion-resistant models that were submitted in statistically signifcant numbers for MOT testing.

The data reveals a few interesting correlations. It's clear which brands skimp on rustproofing, how higher mileage affects the rate of rust, and why some cheap cars fare worse than premium alternatives. If you're shopping for a used car, this is something you'll want to pay attention to, as rust can seriously compromise the safety of your car.

Here's the list of the most rust-prone cars in the UK.

The two key offenders are clear. The Suzuki SX4 and Dacia Duster models from 2010-2014 rust at a rate greater than any others, scoring defect rates above 48%.

Now let's have a look at the cars that absolutely aced the assignment.

The key takeaway here is that contempora Fords, BMWs, and Toyotas (from 2017 ) display vastly better rustproofing than the worst of the worst.

Other points jump out. One is the sheer number of data points, with over half a million Ford Focus tests analysed.

Another is the amount of miles that Brits pile onto Toyota Priuses. Put that down to the ride-share gig economy.

PlateInsight was curious as to why the Suzuki SX4 was such a catastrophic performer and identified a number of reasons. They included inadequate cavity waxing and thin underbody coating that was overmatched by the 'perfect storm' of UK corrosion conditions; winter salt applications and persistent humidity.

The SX4 saw corrosion centre on the rear subframe mounting points and inner sill sections. Water enters through drainage holes that become blocked with road debris, then sits against bare metal. The data seems to show that diesel models fare worse statistically, because they tend to cover higher mileages.

Early Dacia Duster (not the new version imported to Australia) recorded rusty brake lines, corroded springs and then structural issues around the suspension mounts.

At the other end of the scale, the Ford Fiesta excelled. That's because Ford uses fully galvanised steel on all body panels and subframes from 2017 onwards, with the backup of twelve-year anti-perforation warranties. Underbody protection is also excellent, with a wax-based cavity seal injected into sills, door frames, and chassis rails. It clearly works in the most unforgiving corrosion environment on Earth.

Andy brings almost 30 years automotive writing experience to his role at Drive. When he wasn’t showing people which way the Nürburgring went, he freelanced for outlets such as Car, Autocar, and The Times. After contributing to Top Gear Australia, Andy subsequently moved Down Under, serving as editor at MOTOR and Wheels. As Drive’s Road Test Editor, he’s at the heart of our vehicle testing, but also loves to spin a long-form yarn.

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