Given their makeup, cast iron brake discs are susceptible to corrosion from road salt, dirt and water. Many brands claim to offer protection from the elements, but just like the coats we wear – regular, showerproof, storm-proof - there are many different options, each offering different levels of defence. Whilst each brand will market these coatings differently, they can be broadly categorised as – plain, painted, partially coated and fully coated – based on the material used and how and where it is applied.
Plain is, well plain, and offers no corrosion protection. After all it’s plain cast iron and therefore open and vulnerable to anything the road throws at it. Painted, is just that – a thin layer of paint. And whilst this may look great initially, it is effectively just a disguise (as you’ll come to see later!). Just like when you paint a wall at home - any spills or knocks will quickly ruin the effect. Partially coated discs offer some protection, however contaminants, especially salt spray during winter months, can quickly and easily penetrate any unprotected surfaces and eat away at the disc. Which leaves us with fully coated – the approach we take at Delphi.
Why? Because we want to ensure your discs not only look as good as new for as long as possible, but also perform that way too. So we apply a thin layer of a high performance, water and zinc flake based Geomet coating to our discs. We also coat the entire surface of our discs including the top hat, outer rim, internal veins and friction faces. By choosing the best of everything – material and coverage – our fully coated discs offer longer-lasting corrosion protection compared with many painted or partially equivalents, whilst also looking great from behind your alloys. What’s more, because they have no oil to clean off, they’re easier to both dismount and install, saving valuable labour and service time.
So now you know the difference! But what does this really mean in terms of corrosion protection? In a word - a lot! To prove it, independent salt spray corrosion resistance tests were performed on the Delphi disc, the OE equivalent, and five premium aftermarket brands – all fitted to a popular PSA application. The results speak for themselves…
After only 24 hours, the OE - a plain disc - and a premium black painted disc had suffered complete corrosion and were withdrawn from the test. The Delphi disc, on the other hand, showed moderate red ferrous corrosion in only a few areas, and continued to perform strongly.
Fast forward to the end of the test, and at 720 hours, our disc was still less corroded than both the OE and the black painted equivalent at just 24 hours, despite having endured some 700 hours of additional intense salt spray exposure. This is the equivalent of many, many more hours in real-world driving conditions.
So remember, coated discs are not all the same - different brands offer different options with varying degrees of, sometimes huge gulfs in, the protection they offer. That’s why we recommend fitting a fully coated disc such as Delphi’s…a proven long-lasting disc, that’s easier to install, easier to dismount as well as being easy on the eye too.