Over the last few years we are seeing more and more car manufacturers fitting diamond cut alloys to vehicles, they look great and give a bling feel to your most prized possession.  They cost more than standard painted alloys and some believe improve the look of your car.

As a company we have been repairing diamond cut alloys since 2004, that’s 9 years, and in those 9 years we have heard a lot of people’s opinions on what causes the corrosion and discolouration of these alloys.

The defects to Diamond Cut Alloys

Now back in the day these alloys were commonly only fitted to Mercedes, Chryslers and BMW M3s.  And if you’ve owned one of these vehicles fitted with this type of alloy you will know the outcome of the look of these wheels after owning them for a couple of years.  It’s not good!  They develop spider like cob webs under the coating that then turn black and eventually start to flake. This deformation of the alloy most commonly forms on the outer edge and centres of the central badge and bolt areas.

Diamond Cut Alloys Corrosion Issues and Warranty.

We have heard from customers that have owned their car for a few months, bought it brand new and spent an additional ££££’s to have the diamond cut alloys fitted to their car as an optional extra! (in my opinion an optional liability)for them to start to show signs of corrosion in the form of spidering and discolouration under the coating of the alloys with in the first year of purchase. Luckily for the owners,  if this happens in the fist few months of owning a brand new vehicle they are with in their 1 to 3 year warranty period, and can have their wheels replaced unless they have kerbed them. We will touch on this point later.

How the Manufacturer avoids replacing Diamond Cut Alloys under warranty

The warranty period varies dependant on who the manufacturer is.  A few years ago alloys would come under the body warranty and not the trim, giving you 3 -5 years warranty. More recently we have found that alloys are now coming under the trim warranty giving you 12 months warranty which is conveniently far less than the body warranty. We feel the manufacturers have found a way of getting rid of their problem of having to replace these alloys under warranty by placing them under the trim section.

A nice get out for the manufacturer is if you have kerbed your alloys, they claim that the corrosion or the discolouration is due to the fact that you have kerbed your alloy, even though the kerb damage is located to the outer rim of your alloy and the corrosion/discolouration of the diamond cut alloy is located around the inner centre of the wheel nut area, a fair old distance from the damage! This is another feeble get out.

Quite clearly there is a manufacturing fault with diamond cut alloys. The manufactures need to address this issue.

What causes the little white spidering that appears more commonly on the outer edge of the alloy and around the wheel bolt areas?

In order to answer this question you need to understand the make up of these alloys. Now the face of the alloy is lathed so if you look closely you will see little lines going around the face of the alloy.  The inner parts and sides of the spokes are painted and lacquered. Now there is a lot of hear say about the coating that is placed on top of the machine finished face of the alloys and we believe this is a plastic coating, not a powder coat or a wet lacquered finish. If any one has technical knowledge of the coated surface and not an opinion we would love to hear from you.

Once you break the seal of the coating the spider effects start to appear. Now there are many ways that this coating can be broken. When you have a new tyre fitted they use an arm to lever the tyre into place this arm is placed behind and under the alloy, possibly breaking the plastic coating allowing water ingress into the edges of the alloys. The spider effect around the wheel bolts is where the bolts have probably been removed with a high impact ratchet gun which may have slightly caught the alloy creating an opening in the plastic coating, or where the badges have been removed using a flat head screw driver.

Your Nightmare Stories

Over the years we have heard all sorts of nightmare stories from our customers relating to diamond cut alloys, we have tried to help out by offering letters of expertise as to why the damage has happened in order to help with the warranty claim.

We would love to hear your stories and experiences with your local car dealerships and manufacturers relating to your diamond cut alloys

Warranty Goodwill Gestures

Remember a car dealership can offer a goodwill warranty gesture this is negotiated with the manufacturer and it is in our opinion that corrosion on diamond cut alloys warrants some good will from the manufactures and dealerships.

All in all we recommend steering well clear of diamond cut alloys and opting for the standard painted ones.

Article by Steven Lewer-Sotirou