Much has been written about BMW's issues with Cracked Wheels.
The issue first came to the fore with the LA230 19" wheels on the 3 series. As the size became more popular, a number of Sport models were fitted with the LA225 style wheel, sometimes known as MV4's and the issue hit the headlines. The issue wasn't confined to just 3 series, the LA172 'Spiders' on the 5 series have been known to crack as have some lesser sizes and occurences on other models.
The issue was campaigned by BBC's Watchdog and BMW replaced them under warranty. BBS ran into financial difficulties as a result.
What are your options ?
Go to your dealer and get them to 'run the wheel up'. They will see if the wheel is buckled, the tolerance being 0.6mm, and whether it has been kerbed. Either of these and a free replacement is declined.
Wheels can be repaired professionally by welding. The stressed area has to be cut out and refilled with 'new' metal. This is not as expensive as you may think, typically £40-£60
What causes it ?
The state of the roads, potholes, and the unforgiving stiffness of RFT sidewalls all contribute. Instances with conventional tyres fitted are much rarer.
The cracks tend to appear on the inner edges....