The truth about alloy wheel repairs

QUESTION

I’ve just bought a (low km) 2.5 year old A45 privately - so who really is the dumbarse ? 😊

I’ll have to let you know at some stage about a particular Mercedes-Benz dealer who I selected (by geography) to give it the ‘once over’. I paid a large amount of coin to be informed I was buying a ‘car’. But, better than buying a second-hand hand one from a Merc dealer – one of which was certain that Mercedes-Benz ‘standards’ state they can repair deeply gutter-rashed rims and said the wheel will still perform as it was designed…

I was asked “do you intend to track it ?” I retorted with – as if that matters! They never sent me those apparently specific Mercedes-Benz standards on damaged rim repairs. The one I bought had 2 repaired rims – I bought new rims from Mercedes-Benz and the alignment showed there was no issue form its specifications. I was lucky.

On the flipside, the AMG rims were less than a Golf R Talladega rim ($4k – for one) or an HSV rim for my 12-year-old Senator ($2-3k). They must make all their profit on the bozos who buy their cars new then suffer 39% depreciation in 2.5 years. (I probably still paid too much for mine)…

Love your work - Roger

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ANSWER

Mercedes-Benz almost certainly has an internal standard for wheel repair, but they’re not obligated to disclose it, obviously.

I don’t see the problem with repairing a deeply gutter-rashed wheel. Gutter rash is not generally a pathway to failure of a wheel. (If it were, there would be failed wheels everywhere.) Gutter rash is generally just cosmetic damage, and the repair is equally cosmetic. Neither gutter rash nor repair affect wheel performance in any way.

If the damage does knock the wheel alignment out, which is the main risk, it’s usually within the adjustment range, and easy to compensate for in a service bay. Most gutter rash is just a smearing-type interaction with a kerb.

More worrying is pothole impact on wheels with low-profile tyres, which can break the rim, dump the air out and cause loss of control. The lower the profile, the less cushioning there is in this kind of impact.

Even if they powder coat an alloy wheel during the repair process it’s usually just spending 15 minutes at 200 degrees C. So it’s only at a mildly elevated temp (in a metallurgical sense) for a short time and that’s generally not enough to change the mechanical properties of the metal.

I’m not a metallurgist (I’m an engineer) but the basics of aluminium heat treatment are:

• Annealing (to cure work hardening). This generally takes place 300-400 degrees C, depending on the alloy, and the material needs to be at that temperature for 30 minutes to three hours.

• Homogenising (which distributes the elements in the alloy more evenly). This takes place at about 480-540 degrees C.

• Precipitation hardening (which is used to generate the required hardness in some alloys). This takes place at 115-240 degrees C - but the material needs to be at the designated temperature for 6-24 hours for this process to occur. Fifteen minutes is just not enough to make a difference.

So you can see 15 minutes at 200 for powder coating is highly unlikely to affect the mechanical properties of the wheel in any relevant way, in relation to the processes above, because the temperature and/or time at that temperature are too low.

Some people obsess about things of this nature - I get that. And keeping the wheels original is important to some owners - but you always pay through the neck for that. However, if wheel cost is an issue, I’d simply buy aftermarket rims manufactured to the Australian standard, AS1638. The standard is not free, but you can purchase AS1638 here >>

It’s about $100 as a PDF.

This standard is optional (but all of the credible aftermarket wheel makers comply). The performance standards are severe, and fully disclosed. (Unlike with OEM wheels.) Quality aftermarket rims are heaps cheaper.

Here’s a crowd that repairs wheels responsibly on the NSW Central Coast >> The link explains their process for repair.

Hope this helps mate.

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