Some Vanguard DieHards recommended this site. It's free and very easy to use. It provides allocation advice based on your risk tolerance, annual contributions, and years to retirement. Not a 1-1 correspondence with the TSP funds, but close enough. Finally, it provides an estimate of your final account value and an estimate of your worst one year return.
http://easyallocator.com/calculator.aspx
http://easyallocator.com/calculator.aspx