Mostly the Ring I believe. It was mostly suspension, steering, and engine tuning for the 1M.

When I met Dr. Segler in Detroit he said N54 engine testing started in Oct 2009 and the car took about 1 yr to develop. The development time of the engine was very short. In December 2009 the decision was made to build the 1M. Dr. segler championed the project and made all major decisions. Took around 1 year to develop and test the car. M cars utilize the Nurburgring circuit for extensive testing. All the testing needed to be completed in Spring and Summer before bad weather starts. He said the engineers and designers worked very, very hard to complete the project.