Corroding Alloys (2019 Cupra Ateca)

['Little' John]

I've been out cleaning the cars this morning (something that doesn't get done as often as it should). I noticed that on three out of four of my wheels there was some sort of discolouration. I initially thought that I had somehow managed to kerb them despite how far out the tyres protrude. However, upon closer inspection, the lacquer appears to be fine and it seems to be some sort corrosion under the lacquer. Has anyone seen this before and got any ideas what I should be doing about it? Thanks guys.

 

[East Yorkshire Retrofits]

Extremely common on diamond cut alloys

 

[Seriously?]

It's very common; it's called "white worm" and is caused by moisture getting under the lacquer. Even the smallest stone chip can cause it, or where tyres have been fitted.The only proper way to sort it is to have the wheels re-cut.
But it almost certainly will return; and you can only get the wheels re-cut a limited number of times.
Diamond cut alloys look great, but they aren't the most practical of things.

 

['Little' John]

I'm presuming that if I don't do anything about it, then it will get progressively worse. Is it an integrity issue?

 

[East Yorkshire Retrofits]

I'm presuming that if I don't do anything about it, then it will get progressively worse. Is it an integrity issue?

Yes it will, and no it isn’t

 

[SRGTD]

@‘Little’ John; in general terms, diamond cut alloys don’t have great durability and as @Seriously? has said, they’re susceptible to (unsightly) white worm corrosion if the lacquer becomes damaged. It’s not unusual for diamond cut alloys to succumb to white worm corrosion after a couple of years (sometimes sooner), especially on a car that’s used as a daily driver during the winter months; road salt / grit and diamond cut alloys isn’t a great combination if you value the appearance of your alloys. A professional refurb will restore the diamond cut finish (typically a good quality refurb will probably cost around £120 + VAT per wheel), but as @Seriously? has said, the white worm corrosion will very likely return.

Also, be aware that harsh cleaning products (e.g. acid based wheel cleaners) shouldn't be used on diamond cut alloy wheels as such products can attack the diamond cut finish, leaving a dull milky appearance. I suspect many of the hand wash places use harsh cleaning products to speed up dirt removal and the car cleaning process, enabling them to maximise the number of cars they can clean, and also maximise their revenue. So for anyone using these hand car wash places, do so at your peril if you value the appearance of your car’s paintwork and alloys!

Unfortunately, car manufacturers seem to be obsessed with diamond cut alloys and fit them to many (most?) of the cars in their model range. They have a certain ‘bling’ appeal in the showroom if you like that sort of thing but personally I don’t, and I‘d much rather have a set of highly durable powder coated alloys.

 

[Seriously?]

The diamond cut wheels on my current vehicle have never been refurbed and have no kerb rash whatsoever, but the dreaded white worm has still put in an appearance around the centre bores where (I presume) at some time a tyre fitter has flicked the centre cap out with a screwdriver.
It doesn't take much to allow the moisture under the lacquer.
When they really begin to annoy me, I'll get them refurbed and power coated.

 

[SRGTD]

The diamond cut wheels on my current vehicle have never been refurbed and have no kerb rash whatsoever, but the dreaded white worm has still put in an appearance around the centre bores where (I presume) at some time a tyre fitter has flicked the centre cap out with a screwdriver.
It doesn't take much to allow the moisture under the lacquer.
When they really begin to annoy me, I'll get them refurbed and power coated.

The bare metal diamond cut / polished finish doesn’t provide a good key for the ‘protective’ clear lacquer to bond to the wheel, hence the issues with moisture creep and oxidation under the lacquer.

Some years ago, I had a similar experience to you. I had two centre caps on a mk6 Golf replaced under warranty - ironically because the centre caps were suffering from white worm. Shortly after they were replaced, the two (diamond cut) alloys with the new centre caps suffered from white worm corrosion around the centre bore. I always suspected the dealership removed the old centre caps by using a screwdriver to prise them out, although I’ll never know………….

 

[Seriously?]

The bare metal diamond cut / polished finish doesn’t provide a good key for the ‘protective’ clear lacquer to bond to the wheel, hence the issues with moisture creep and oxidation under the lacquer.

Some years ago, I had a similar experience to you. I had two centre caps on a mk6 Golf replaced under warranty - ironically because the centre caps were suffering from white worm. Shortly after they were replaced, the two (diamond cut) alloys with the new centre caps suffered from white worm corrosion around the centre bore. I always suspected the dealership removed the old centre caps by using a screwdriver to prise them out, although I’ll never know………….

Generally speaking (apart from replacing the caps themselves), the only reason they need to be removed is when new tyres are fitted, in which case they could just as easily be pushed out without using a damaging pick/lever/screwdriver from the back once the wheel was off the car.