I spent some time searching the Internet for information about chainline. I found some good information about the front chainline, but I did not find any information about the rear chainline. What is the rear chainline when using Shimano 130mm and 135mm 9-speed freehubs? And, Is it desirable to match the front and rear chainline? Are there instances when it is not desirable to match the front and rear chainline? Is the chainline of mountain bike cranks (47.5-50.0 according to Shimano) larger than the chainline for Shimano rear hubs? If so, then why not use a wider (tandem) hub?