ZipZap Monster Truck Duals

  Introduction
monster truck with Hummer H1 body and rear duals
click on the image for a larger view 		     Driving down a country road in Indiana this Spring, I chanced upon a farm tractor with wide dual wheels.  So why couldn't one of my ZipZap monster trucks have duals?  Here's my experiment.  
  Parts
     The following parts are required per wheel:
  • one 16-mm piece of 3/16-inch diameter brass rod (plastic rod might work as well)
  • one 8-32 hex nut
  • one 2-56 x 1/4 machine screw
  • one ZipZap Monster Truck wheel and tire
  Tools
     The tools needed for this project are:
  • Dremel tool, or equivalent, with cut-off discs
  • small pliers or a small vise
  • 1-72 thread tap
  • 2-56 thread tap
  • 8-32 thread die
  • no. 54 drill
  • no. 50 drill
  Building the Axle Extension
  • With a Dremel tool and cutoff discs, or a razor saw, cut the brass rod to a length of 16 mm.
  • At one end of the rod, remove sufficient diameter to cut 8-32 threads for the hex nut.
  • On the same end of the rod, with a no. 50 drill, drill and tap for a 2-56 thread.
  • At the opposite end of the rod, with a no. 54 drill, drill and tap for a 1-72 thread.
  • Removed all metal burrs and true-up the ends of the rod.
  Assembling the Wheels
  • Attach the 8-32 hex nut to the rod.
  • Removed and store the wheel nut from the inside wheel.
  • With the inside wheel in place, carefully thread the brass axle extension onto the axle.
  • Place the outside wheel over the 8-32 nut.
  • With a 2-56 machine screw, attach the outside wheel to the axle extension.
monster truck with Hummer H1 body and rear duals monster truck with Hummer H1 body and rear duals
  Conclusion
If racing MTs is your thing, then this is not for you.  It is not apparent that dual wheels are helpful in going fast.  They do, however, keep everyone else from getting around you!  As you can see from the pictures elsewhere on this site, my MT has two gearbox changes, the result of which is a slower speed.  I cannot see that my MT goes that much slower because of the duals, but then, I want it to go slow anyway.
For a non-articulated MT, the dual wheels provide additional width which helps prevent rollovers.  While I've yet to do extensive rock climbing with this MT, the duals do seem to otherwise lend a stability the stock MT does not have.