The Story Of BIGFOOT 8

 

Building BIGFOOT 8 - The First Stage 3 Monster Truck

A Note From BIGFOOT creator Bob Chandler:  Before you start reading my article, I must remind you that I am not an engineer, so some of the language is not as technical or precise as I feel it could be.  I hope it is all correct.

Prior to the building of BIGFOOT 8, I knew our industry had to make a major change because of the type of shows and races promoters were asking Monster Trucks to do. At the time, we were still using Stage 1 & Stage 2 Monster Trucks, which had limited suspension travel and usually had a big stack of heavy leaf springs with many shock absorbers.  Drivers were getting hurt on a somewhat regular basis while performing at these Monster Truck events.

Most of BIGFOOT 8’s changes that were made to improve Monster Truck safety, also made them faster and more controllable, and even improved their capabilities during races.  This was a very good thing for our industry and the next step in the progression of Monster Trucks.

BIGFOOT 8 was the first Stage 3 Monster Truck. It was also the continuing progression of BIGFOOT’s leadership and professionalism in our industry.  Today, most Monster Trucks essentially use this same basic design, which was not unique to Monster Trucks. It was adapted and updated from many other Motorsport vehicles.

At the time of BIGFOOT 8’s creation, Dan Patrick was a part-time employee of BIGFOOT and was a lot of help on this project, mainly because he had experience cutting, bending, and welding tube chassis.  Prior to his time at BIGFOOT, Dan built several tube chassis for his funny car & tractor pulling vehicles.  Dan now builds some of the best Monster Truck chassis in the world.  I believe he learned a lot about Monster Truck technology from his time at BIGFOOT, but we also learned a lot from Dan.

I wanted to improve Monster Truck suspension, particularly to make BIGFOOT safer for our drivers.  I also wanted to make them faster and lighter, but I initially intended to use a bigger, heavier, c-channel upper frame with attached tube chassis and cage.  Jim Kramer and Dan Patrick convinced me to make the entire chassis tubular.  Dan gave me a drawing of a funny car tubular chassis.  The drawing was only a 2-dimensional side view of a funny car frame.  I ultimately incorporated his drawing into my AutoCAD program and added the entire Monster Truck chassis and cage to it.  I eventually updated it to a 3-D drawing.

Each morning, I would bring the drawing I produced the night before at home to work and then ask Dan, Jim and Andy Brass if they had any suggestions or changes.  I always incorporated their positive suggestions. Later I used a free internet FEA (Finite Element Analyses) program to check for weak areas in my frame and cage designs and for any unnecessary tubing.

The gas shock suspension design on BIGFOOT 8 came after Jim and I watched an Off-Road Racing Ford Ranger at a Ford dealership out west.  The vehicle had a very long travel Nitrogen gas shock suspension.  I contacted the individual who manufactured them, Bob Giese, and ended up buying his shocks for BIGFOOT 8.  We eventually bought Bob’s entire stock of parts & his shock design because he was not really interested in expanding his business and manufacturing shocks for Monster Truck applications.

To get these gas shocks to work the way I wanted them to, I then designed and patented a cantilever suspension system for BIGFOOT 8 (US Patent #5,108,127 Vehicle Suspension System).  In my design, even though the shocks themselves would only travel 14” at that time, my suspension traveled a greater distance.  This was accomplished with my computer-generated cantilever design.

Besides giving the axles more travel than the shocks, my cantilever design gave the axles, when in the extended range, more travel distance than the shocks, thus less control from the shocks.  When the axles were in their compressed range, the shocks traveled a greater distance as compared to the axles, giving the shock more control.  The shocks had progressively more control of the axles as the axles traveled to their compressed areas.  The cantilever suspension design gave BIGFOOT 8 more positive tire contact, especially after airborne conditions.

The cantilever design was accomplished using my AutoCAD program and many hours on the computer.  Years later this cantilever progressive configuration was eliminated and was incorporated directly into our shock design.  Jim, with his extensive hydraulics knowledge, redesigned & updated these gas shocks so we would eventually have even more travel.  Jim also put bigger components for our Monster Truck application.

All of these design applications were very important to Monster Trucks because of our un-sprung to sprung weight problem.  Monster Trucks, as compared to most other vehicles, have a greater un-sprung weight ratio compared to sprung weight.  That means the un-sprung weight (axles, tires, wheels, etc.) are heavier than the sprung weight (body, frame, engine, transmission, transfer case, driver, etc.)  This configuration does not permit Monster Trucks to control their suspension the way most vehicles suspensions perform.

BIGFOOT 8’s 4-link suspension was also designed using my AutoCAD program.  The length of the 4-link bars, and their placement (mounting points) on the axles and on the frame was also done with a lot of hours on the computer using AutoCAD.  Throughout the suspension travel on BIGFOOT 8 the axle yokes & the transfer-case yokes stayed virtually parallel to each other throughout their travel.

During all this time, I also received technical advice from my friend Andy Wittle, a local hands-on Engineer.

Bob Chandler
BIGFOOT 4X4, Inc.