Again, you should not be shrinking your transaction log as a part of normal operations. When you backup the transaction log, the process will truncate the log, which is not the same thing. That means it removes the committed transactions from it, leaving only the open, uncommitted transactions, thus mostly emptying the file, but not reducing its size on disk. New transactions will then start to populate the space in the file just emptied (this is simplified; the process is a little more complex than this, but for our purposes here, this is close enough to what happens).
If you set recovery mode to simple, you will not be able to run transaction log backups. Simple mode simply means that the transactions will be truncated out of the file as soon as they are committed.
SQL Server 2008 R2 will truncate the log after a successful log backup just as the same as earlier and later releases of SQL Server.