If you want to run extremely low air pressure off-road then you need a rim lock.  There is a reason that all other dirt bikes come with them.  Without locking the rim to the tire on a tube type assembly, with low air pressures the rim will spin inside the tire tearing the valve stem off of the tube in the process.  A rim lock solves this problem.  A custom lock had to be designed for the 4.5" x 14" TW wheel.  Machined from aluminum and weighs about 6 oz.  Comes with mounting hardware and 6oz of black stick-on weights if you want to rebalance.