Those are just black? They look pretty reflective, almost like a black chrome.

 

The problem with powder coating is that many powders require different temperatures to melt, varies anywhere between 250-1000*F. There are various types: polyester, polyurethane, polyester-epoxy, epoxy, and acrylic each with it's own specific melting point. At what temperature and for how long the wheel sits in the oven is up to the powder coater and the type they use.

Aluminum changes crystal structure at approximately 410*F. Rims like RPF1s and Rays forged rims etc are made strong and ductile through specific crystalline alignment (hammering- old school forging and new- pressing mechanically or hydraulically).



RPF1s barrels are pressed into shape (see above m.a.t. process and crystal alignment) to achieve forged like properties. When rims are powder coated depending on the temperature of the heat cure process the crystal structure can be changed dramatically. When aluminum alloy is heated over 275*F the properties of the alloy starts to change. End result is a rim that's more brittle with a significant lower tensile strength.

 

This is true, however there are powders on the market now that will cure at lower temperatures for shorter periods of time. Many wheel manufacturers offer powder coating as standard, because of the fact that it is more durable than paint, and for the fact that when it is done correctly it does not seriously affect the strength of the wheel.

In short, if the wheels are left in the oven for too long, or at too high of temperatures, the wheels will become more brittle. Ideally one would hope that you would not need to powder coat your wheels more than once.