Monster Mayhem Discussion Board FAQ

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Temporary faq

Last Updated on: December 28, 2012

Who makes monster truck chassis?s and components?
Most teams build in-house chassis?s for their trucks. Patrick Enterprises, Race Source, Concussion Motor Sports & Carrol Chassis are primarily the most popular builders in chassis?s and components. Often times, fabrication/welding shops will create them by request. AutoCAD, Computer Aided Design, is used to create a 3D computer model of each chassis and component to insure of its rigidity, strength, weight, safety, and ease of use. A design may take upwards of 800 hours.

Who makes the bodies for monster trucks?
GTS Fiberglass, specialists, or in-house

Are bodies painted or wrapped?
Because of the expense and time for paint, wraps are cheaper and quicker to apply. Custom graphics are time consuming if painted on, not to mention expensive. As for painting, monotone or two-tone will work fine. After that, its placing and positioning decals/stickers.

What is an R.I.I.?
R.I.I., better known as Remote Ignition Interrupter, is used in the safety of monster truck racing. Onboard is a receiver that is controlled from the ground by officials or team crews by way of transmitters. This device shuts all power off to the truck just like a kill switch. Such vital equipment allows track/safety crew to perform extrication of the driver, prevent runaways, fluid leaks, and fires. Each R.I.I. and transmitter use different frequencies, giving each truck their own signal. Before each run, officials and drivers do tests to insure they are functioning properly.

What seats are used?
ISP, ButlerBuilt, Joie of Seating and Sparco. Other brands will work as long as they provide driver comfort and accept 5 and 6 point harnesses.

What is a harness?
A harness consists of 2 lap belts, 2 over shoulder belts, and 1or 2 cradle belts with a central connector locking them together. The term points, refers to how many places the harness attaches to the truck. The belts are adjustable to help secure the driver tight to the seat.

What transmissions are used in monster trucks?
Monster trucks run automatic transmissions. Power Glide, Turbo 400, C6, and TorqueFlite A727 are modified for strength, and durability. They can be left as automatic, or the driver can shift it his/herself without a clutch?.. this being done with switching automatic to manual (standard) valve body. Lenco is also used and uses either air or a lever to shift.

What are transfer cases?
Transfer cases bolt up to the transmission, distributing power to both front and rear drive axles. Commonly called drop transfer case, the case drops down far enough to cut pinion and drive shaft angles allowing for optimum performance and durability. They come in various drops to suit allowed space. Profab, SCS Gearbox, or custom in-house chain drives are found in today?s trucks.

What kind of motor is in a monster truck?
Today?s trucks run various motors, naturally aspirated and (supercharged) blown alcohol injected. Maximum allowed cubic inches up to 575, horsepower range of 1100 - 2000+, any type of header/exhaust.

Are there diesel monster trucks?
Yes, very few.This is mostly because of the fumes diesel engines emit. Most modern day arenas are now outfitted with carbon monoxide detectors and are monitored during the show. If they go off, the show is temporarily "stalled" until the filtration system can catch up.

What do drivers wear?
Nomex/Carmyth under clothes(under helmet hood optional), 1 or 2 piece fire suit, helmet, gloves, shoes/boots. HANS (Head and Neck restraint) or collar. All worn items are tested and rated for fire and safety standards. Helmets are Snell or DOT rated.

How do you steer a monster truck?
2 hydraulic rams each mounted on front and back drive axles. With the use of orbital hydraulic valves, hydraulic fluid is distributed to each ram making the truck steer left or right. Rear steering works the same way, but with an electrical toggle switch running the valve left, right, or self center.

What is a tie rod?
Tie rods are adjustable rods with heim joints connecting front and rear steering knuckles together. Holding the knuckles together allows all 4 wheels to align in a straight line. Also, the tie rod pushes and pulls when steering the truck.

What are the tires?
Found on farm, construction, and forestry equipment, the tires are terra tires. Due to their size, they are classified as flotation? meaning they spread over a wider path to avoid compaction and sinking. They are 66? tall, 43? wide, and fit a 25? rim. Firestone and Goodyear(now Titan) create these massive tires. To make them lighter, teams will shave off excessive rubber and craft them to desired bite, and tread depth for different conditions and surfaces. One tire may take upwards of 40 hours to do. Unshaved tires are between 800-900lbs, and shaved weigh close to 700. Newly developed, Sudden Impact Racing molded a lighter tire weighing in at 425lbs.

How big is a monster truck.
Monster trucks can sit as high as 11?, as wide as 13? and weigh 9,000-11,000. Of course this is give or take estimates.

Who makes shocks, and what are they filled with?
In-house custom, Patrick Enterprises, RaceSource, Combs, and King. Shocks are charged with nitrogen gas at around 400psi and have upwards of 28" of travel.

What?s the fastest monster truck?
?Kirk Dabney (OverKill), 90.44 MPH in February 2011
? Dan Runte (BigFoot), 86.56 MPH in September 2010
? Kirk Dabney (OverKill), 84.92 in 2009
? Dan Runte (BigFoot), 84.49 MPH in 2009
? Randy Moore (War Wizard), 84.382 MPH in August 2005 ? Dan Runte (BigFoot) 69.30 MPH in 1999

Are there onboard fire extinguishers?
Yes. Trucks are equipped with a small user bottle for less threatening fires. Also fire suppression systems are available and routed through areas of the truck prone to fires. This system uses a switch or pull type activator releasing the contents, thus extinguishing the fire.

How can I become a driver/crew member?
Today?s teams require experience, technical training or a CDL license. If you do not have these, that?s ok. Best solution is to contact promoters and teams and volunteer to help, this way you can gain a little experience. Talk to everyone you can, help out, get your name out there. Every little bit counts. DO NOT be afraid to ask questions or for help!!! Team work, communication, patience, positive attitude and shared information is what makes a top notch team. Remember, this is both physically and mentally demanding work.

What kind of axles are on the truck?
Rockwell F-106, Rockwell 2.5 ton, and Rockwell 5 ton. Housings can be either heavy stock, or light sheet metal. Also, planetaries are added to the ends, acting as gear reducers and also aid in the steering/handling. Available planetaries are Clark 20 Ton, Rockwell PS-115, PS-250, and Pettibone. As a whole unit, some axles already have planetaries installed on them.

How do you haul a monster truck?
Teams use Class A CDL rigs. Some teams prefer to use toter homes equipped with living space. This eliminates the need of a Class A CDL, therefore classifying them as a registered motor home. In tow, are custom outfitted drop trailers filled with everything needed to maintain the truck. For the monster truck to fit inside, smaller transport wheels are bolted on. For added clearance, the shocks are discharged of nitrogen gas.

What are planetaries?
The planetaries are wheel hubs on most monster trucks. An input shaft entering one side with a center gear (sun) on the inside the hub end. Three outer orbiting gears (planets) will engage the center gear. This engages a ring gear fastened to the outside case, transferring the shaft torque through the planet gears and on to the ring gear. The ring gear is fastened to the hub. The hub mounts the wheel and tire by way of lug studs and lug nuts. On monster trucks, the planetaries along with steering knuckles and universal joints let the vehicle turn left or right.

How do I get autographs? At event pit parties, or small shows/displays/car crush.

Who does the wiring for monster trucks?
Painless Performance makes wiring to suit the needs for every truck. Every wire is marked in both color and lettering to make the process as easy as possible.

Where can I get to ride a monster truck?
Most events have ride trucks on site that are built specifically for passengers. Seats, seatbelts and a roll cage are mounted in the back for passenger safety.

I see trucks with the engines in different places. Why is that?
Balance of the truck, handling, center of gravity, and driver preference.

How do you stop a monster truck?
Braking is done through the drive shaft/pinion area on the axle. A brake rotor is mounted on the drive shaft/pinion allowing it to turn. With the caliper mounted on the axle, the rotor turns freely between the pads while the truck is in motion. Due to the weight and speed of the truck, the rotors will glow a bright red when force is applied.

What exactly is a Monster Truck?

Last Updated on: March 28, 2008

Current monster trucks are purpose built 4 wheel drive vehicles that handle a variety of tasks (Racing, Freestyle, etc.) Older monster trucks also known as "old school" typicaly were stock trucks that were heavily modified. Though no 2 trucks are alike their are some basic outlines that can be said :
Height - Approximately 12' / 3.6 Meters
Width - Approximately 12' / 3.6 Meters
Length - Approximately 20' / 6 Meters
Weight - Approximatly 10,000 lbs / 4500 Kilograms
Tire Size - 66"?/ 1.7 Meters (tall) X 43"/ 109cm (wide) on a 25"?/ 63.5 cm wheel
Motor Type - Custom built blown alcohol injected V8
Motor Size - Less than 575 cubic Inches / 9.4 Litres displacement
Horsepower - Anywhere from 1200 - 2000+
Top Speed - Approximately 70 MPH / 113 KMH
Suspension Travel - 18"/ 45.7cm - 30"/ 76.2cm - Fully adjustable Nitrogen or Coilovers.
Chassis - Custom tube
Body - Fiberglass with a Lexan Windshield
Fuel Capacity - 16 - 22 Gallons/ 83 Litre Fuel Cell
Fuel Type - 99.9% Methanol (Alcohol)
Safety - RII (Remote Ignition Interrupter), On Board Fire Extinguisher System
Driver Safety - 5 Point Racing Harness, Fire Resistant Suit, Shoes and Gloves, Racing Helmet

What is an R.I.I.?

Last Updated on: March 28, 2008

R.I.I. stands for, Remote Ignition Interrupter. This unit is one of the biggest safety devices in a monster truck and actualy contains 2 parts. First is a specialized radio receiver mounted in the truck. The second part is a hand held transmitter that is held by a track official. The transmitter looks like a walkie talkie but instead of talking on it, it broadcasts a special signal when the "talk" button is pushed that will shut down the truck in the event of a problem such as the truck veer off the track and/or the driver become incapacitated. The R.I.I. will only shut off the engine and all of its electronics. Everytime a truck goes out to preform the R.I.I. is tested to make sure it is working properly.

On Board Fire Extinguisher?

Last Updated on: March 28, 2008

There are actualy 2 on board fire extinguishing system. First is a 2lb. hand held unit that is in easy reach of the driver should the occassion arise that it is needed. The second is a larger unit that is also easy to reach but it is activated by pushing a plunger. When done the exinguisher dispences in critical areas of the truck (driver compartment, engine area, fuel tank, etc.)

What kind of seat belt is used?

Last Updated on: May 24, 2008

A 5 point harness is a form of seatbelt that contains five straps that are mounted to the trucks frame. This is what holds the driver in the seat and use a quick disconnect mechanism to allow the drivr to quickly exit the vehicle. They consist of a 3 inch lap belt, 3" shoulder harness and 2" or 3" single sub belt. These seat belts come with ends that can be used as either Individual Wrap Arounds or Bolt Ends. There is a newer belt style which has a ratchet mechanism to get the belt tight and will not loosen up during the run, unlike the standard "pull type" belts.

Link Suspension Encyclopedia

As in seen in 4WD Toyota Owner Magazine July/August 2010

By Your's Truly

No matter what type of vehicle we drive, the suspension is the single most important element in regards to how it handles. With a poorly designed suspension, even a well-built rig won?t go the places that it should. Yet it wasn?t long ago that leaf springs were high tech. Shackles were mounted in front of the tires, and leaves were under the axle. Trends have evolved to reverse both: conversion kits to spring over our trucks and put the shackle in back for better all-around performance. But we?ve seen further evolution in our vehicles with the advent of linked suspensions. Like our older and sometimes wiser siblings, desert racers have perfected this evolutionary stage and are enlightening us about how to handle the rough stuff better, while drag racers are showing us the art of ?The Launch.?

Unlike a leaf spring, which locates or holds the axle under a vehicle while suspending it over the tires, a linked suspension only positions the axle under the vehicle, relying entirely on another separate system to hold the body and chassis above the axle. The location, angle, and length of those links in relation to the rest of that vehicle affect how that vehicle will drive down any given road.

There are quite a few companies out there that have some decent leaf springs. And while leaves work great for their cost, they are limited in what they can do for a vehicle. Drag racers, Baja guys, W.E. ROCK, OEM?s and even clumsy monster trucks all use link type suspensions. Even newer daily driven trucks are linked in one way or another. An 80, 100 and 200-series Land Cruisers, FJ Cruisers, 4Runner are linked, sometimes front and back (80-series).

So why are links so awesome? By nature they have the ability to enhance driving characteristics and attributes of your choice. Whether you?re building to drift around corners, drag race or tear through Baja, a linked suspension has the ability to be tailored to the needs of the sport or recreation of your choice. If built with adjustment in mind, minor driving characteristics can be changed with a wrench and a few spare minutes.

Let?s consider short track-type racing, comprised of many sharp turns. CORR trucks are typically set up for more traction off the line and coming out of turns. For this we?d set up our suspension to help launch the vehicle when you hit the gas and maybe even oversteer the rear of the vehicle to help get around corners. Rock crawlers, on the other hand, build theirs to help apply extra traction while going up steep hills. A vehicle that sees a lot of highway use would typically be built with little to no roll steer, so that it travels straight and doesn?t wander in the lanes. It?s this kind of design and forethought that most amateurs don?t think about when building a vehicle. Many Baja designers feel strongly that a neutral suspension is the best all around setup for their application because it?s the most predictable or benign. This allows them to do all of their tuning with shocks, springs, anti-sway bars, wheelbase and track width.

In case you haven?t noticed a pattern, there is no such thing as the perfect suspension, meaning no one suspension can be great at everything. Designing a suspension for your needs will be a matter of knowing what you want and knowing want you can live without. You can?t have mad-crazy wheel articulation and still beat a Lexus IS-F around a road course. It is a matter of compromises.

Many handling traits can be measured through a traced line running though the links that attach your axle to the vehicle to an imaginary point, through which force is applied. It is the location of these points in space, in relation to the rest of the vehicle, which cause it to react to circumstances. Some of these points are seen when viewing a vehicle from the side and others from above. The Instant Center (IC) for example, is a point in space, when viewed from the side where links placed on top of the axle and links placed at the bottom converge to form a single point where force can be measure from. This point can be anywhere the designer wants it, from twenty feet in front of the vehicle, to the output shaft of the transfer case. Ever notice that some crawlers have a tendency for the rear tires to hop on certain hills? A characteristic called Anti-Squat (AS) is a key player in wheel hop. Maybe you?ve noticed that your own vehicle jacks sideways pretty hard on certain types of bumps while screaming across the desert? It could be that your Roll Center (RC) is a little too high. Let?s look at things a little deeper.

When your vehicle is viewed from the side, the IC is a point in space where the upper and lower links converge. It is where we can measure the transferred force from both links and put just a single load point on the vehicle when under acceleration, a point in space where forces from the converging upper and lower links are applied to the chassis. The only concern the Instant Center has on a vehicle is in respect to Anti-Squat. Some people design around the IC by saying the IC should be at the water pump or some other point. The problem is, that only works as a comparison if the comparing is of two similar vehicles.

Anti-Squat is the amount of force applied to the links that will resist the rear squatting under acceleration. When you step on the gas (from either a standstill or while moving forward) to accelerate and the rear of the vehicle either drops down or props upwards. By adjusting the location of the Instant Center you change the amount of AS. Seen another way, Anti-Squat is the amount of force placed on the links from the weight transfer of acceleration. When you accelerate weight is transferred from the front axle to the rear axle. There are two things that will keep the rear suspension from compressing because of the extra load transfer. 1: the springs themselves, 2: Anti Squat. With a 0% anti-squat all of the weight transfer goes to compressing the springs. If the springs are stiff they won?t compress much and if they are soft they will compress a lot. If you have 100% AS all of the weight transfer goes into the links of the vehicle and none of it goes to the springs. Because of this the suspension will neither compress/squat nor extend/raise. If you have 60% AS, then 40% of the weight transfer will go into the springs and 60% will go into the links. If you have less then 0%, aka negative amount of Anti Squat, a.k.a. Pro Squat, the rear suspension will squat more than the spring rate would infer.

To measure the AS of any linked vehicle you first need to know the height of the center of gravity followed by the wheelbase. From the side draw a line across the length of the vehicle at the height of the CG. Next draw a vertical line from the contact patch of the front tire up to the line indicating the CG. Now draw a diagonal line from the contact patch of the rear tire to the intersecting point of the CG and the vertical line of the front tire. That line is the 100% AS line. Next draw a line from the contact patch of the rear tire forward through the IC and continuing through the vertical line of the front tire, this would be your AS line. If your AS line intersects the front tires vertical line at 30% of the total distance from the ground to the 100% line, then you have 30% AS. In other words, if your AS line intersect the front tires vertical line at 30? off the ground with a 40? CG, then you have a 75% AS. If the measured distance from the ground to this point is 20? then you have 50% AS. If it?s 10? then you have 25% AS.

Many desert guys run around 20-50%. Drag racers have been know to run all kinds of AS numbers from 50 to 140%. As rock crawlers, we?ve slowly been adjusting the amount of AS we use on our vehicles. Just a few years ago we ran numbers above 100% like the drag racers. Today more common numbers are closer to 50-80%. For your home-brewed application an adjustable link bracket will help you dial in what is best for your needs. What?s the magic number? You tell us what works best for you and that?s the magic number. Just remember the three contributing factors: height of center of gravity, tire size and wheelbase. To accurately measure the height of the CG please visit the links below.

An imaginary line running through intersecting points of a suspension, through which either the front or rear reacts, if the vehicle were held fixed. It is this line between these two points in which the suspension rotates about or moves around. In other words it is the line your suspension swings from.

On a triangulated four-link, assuming both upper and lower links are triangulated, the converging point of the upper links just behind the axle and the converging point of the lowers form the needed two points in space to draw the intersecting line that is the Roll Axis. On a suspension with a panhard bar, this line would be determined by drawing a line though the points that are the center of the panhard bar and the converging point of the lower two links. Generally speaking, a flat or slightly negative angled sloped axis is desired. It is also this line or axis, which determines the amount of oversteer or understeer your axle has. If this slope rolls downhill toward the center of the vehicle you have a negative Roll Axis and your axle will have understeer characteristics. If this slope rolls downhill away from the center of the vehicle then you have a positive angle and therefore oversteer characteristics.

Roll steer can be felt while traveling down most any road. The roll and swell of most roads can be felt as it forces the body to lean from side to side, even while travelling in a straight line. It is when the body leans that roll steer takes effect, causing the axle?s angle in relation to the frame to change and thus have a steering type effect on the vehicle. Oversteer: your suspension causes your axle to oversteer a turn, meaning you turn more than the input of the steering wheel infers. Example: while in a left-hand turn, the body will roll out of the turn to the right. If your rear axle has oversteer, it will turn outward and cause the rear end to come around quicker than it would have otherwise. When you want it, it?s great, but when you don?t, it?s really annoying. A vehicle with solid axles front and rear will drive much nicer down the road with a little understeer.

Vehicles with oversteer typically wander in the lane, which makes for constant steering corrections while driving. If you find yourself with oversteer in your front suspension, then you can compensate by building understeer in the rear. If your Roll Axis is downhill towards the center of the vehicle, regardless of front or rear suspension, then you have a negative angle or understeer. If your Roll Axis points downhill away from the center of your vehicle, then you have a positive angle or oversteer. Many designers try to build a little understeer into their systems, because it seems to be more predictable and benign. It also has a tendency to track straighter and wanders less at speed. However, if you need to get around corners quickly, like a CORR truck, you may find that you need oversteer from the rear suspension to help slide you around corners.

The Roll Center is the point through which the body wants to rotate about the axle, or the point that the axle supports the body laterally. It is again, an imaginary point directly above your axle that intersects the Roll Axis. In that regard it is just like the IC but from a different perspective. It can also be thought of as Anti-Roll, if the Roll Center is at the Center of Gravity there will be no body roll and if the Roll Center is lower than the CG but higher than the ground, then some load from cornering will go into the springs. If, however the Roll Center is on the ground, then all of the cornering load will go into the springs. In other words the higher the roll center the less body roll you get when on side hills and cornering.

However, with a high Roll Center you increase the amount of sideways movement applied to the body from the axle?s movement. This is mostly noticeable at high speeds while traversing cross-grain sections of desert. In other words, a high Roll Center can push your truck sideways when one wheel compresses at higher speeds. In rock crawling, your axle will simply move a bit more to the compressed side then the other when articulated and you?ll never notice any sideways forces due to such a slow overall speed. Desert guys tend to use a lower Roll Center, it may be because it?s easier to package or it may be because it reduces the lateral force on the truck. They tend to compensate for this lower roll center and body roll by adding additional track width via wider axles, anti-sway bars and/or stiffer springs. However at slower speeds like rock crawling, a high Roll Center helps maintain stability without having to add additional components like anti-sway bars and stiffer springs.

In many respects this is similar to Roll Axis, but is measured by the height of the front and rear Roll Centers. It is these two points that form the Vehicle Roll Axis. All though there are many factors in getting a vehicle to handle better, it is generally accepted that a flatter Vehicle Roll Axis will handle more predictably. It is also commonly accepted in the race world that the more equally loaded the tires (same amount of force) both inside and out, the better the traction and handling.

There are ways that handling or the loading of the tires can be improved. One: adding stiffer springs; two: adding an anti-sway bar; three: rebuild and raise your Roll Centers. This topic can get a bit complex, so we?ll leave it at that.

Roll Angle is simply a measurement of how much the body leans to one side while in a turn. A higher roll center can help reduce this number, however so can stiffer springs and or an anti-sway bar.

This refers to the vertical distance between link mounts. As a general rule, the vertical separation of the links at the axle should be 25% of the tire diameter. This is to help handle torque from the axle and ensure less axle wrap. As for the separation at the frame, the amount of desired Anti-Squat will determine this number. Think of the separation as leverage on the links and brackets. The closer together they are the more leverage or force is applied to them, which means you need to make them stronger, both link and bracket. Also the stronger your motor is, the more torque it?s applying to those links.

For the most part, a long link measures at a starting length of 32?. This would be the typical long arm suspension that many mainstream companies speak of. Many people find that they prefer even longer links. One of the advantages of a long arm suspension is that as the suspension cycles the angles of the links change less. This keeps the characteristics of the suspension from changing as much, so that the intended driving characteristics remain more constant though out the suspension?s movement.

The length of the uppers is also important. Many feel strongly that protecting the angle of the u-joints on the driveshaft is very important, so they build the length of their upper links close to the same as the lowers. The advantage here is you maintain the u-joints angle in relation to the pinion, which helps longevity. The down side is that as the suspension cycles downward the Instant Center changes and the Anti-Squat can increase.

By reducing the length of the upper links you have the ability to fine tune where the IC is during the suspension cycle and thus the anti-squat as well. If you have the uppers about 80%-ish of the length of the lower when viewed from the side, you can maintain a steady AS number through the suspension cycle. If you push the uppers back to 70%-ish you can get the AS numbers to reduce as the suspension drops and increase when the suspension compresses. This can help to stabilize your vehicle in steep climbs as well as help rear traction as the wheel compresses while hauling butt through the desert.

However the most common agreed upon method of design is to always keep the lower links as flat to the ground as possible. This will help eliminate any strange jacking and unloading of the links while in hairy situations. A steep angled link can have some strange effects on a vehicle; sometimes the axle will walk under the vehicle while on a steep climb. This can be a scary experience, as the axle continues to climb it pushes under the vehicle, propping the rear into the air and making for a very unstable and scary experience.

Limit straps can be used for many things. They can be used to stop your axle from over extending those expensive shocks, or to stop your suspension from moving downward so much that your drive line (u-joints) become bound up. If you have excessive AS numbers a limit strap can be used to limit how much the axle pushes the rear of the truck upward. This is used wisely by many comp guys that desire the instant traction a high AS offers, but don?t want the axle walking under the truck that a high AS can give on a long slow articulating climbs. Some think of it as a Band-Aid, but it works.

When you hit a bump in the road and the steering wheel and tires change direction and cause you to have steering input to stay on course then you have bump steer. Your suspension soaks up those bumps by moving upward, known as cycling. Since your steering is attached to the axle, it too cycles, just like the suspension. However, when your suspension and steering don?t cycle along the same given path, one system will win out over the other. Since the steering system has a pitman arm that also rotates, and the suspension has fixed points, the suspension will win the fight and force the steering system to follow. So your suspension is causing your steering linkage to change in length, by pushing and pulling on it, which is why your steering wheel turns in your hand when you hit a bump. That?s why it?s important to make both the drag link and panhard bar the same length and sit at exactly the same angle. If for some reason, like a packaging constraint, you can?t get both the same length, make sure they are at least sitting at the same angle. The angle is more important than the length.

From a rock crawling perspective, wheel recession is when the front end of your vehicle is forced upward while your front tires are up against a rock. Example: While climbing a small hill one tire meets a ledge. Your rear tires push you forward, but your front tires don?t climb but rather the nose lifts into the air stretching your front suspension until it?s nearly maxed out, only then does the front start to climb. The likely cause of this is? The angle of your lower links is perhaps too steep in relation to the ground. As the rear tires force the front tires forward and into a rock face, the angle of the lower front links forces the front end up, worsening the angle and compounding the problem, and now you?re looking at the sky.

There are two ways to combat this. 1: build your lower links closer to parallel with the ground, so that when you hit a rock face the force pushing on that link is closer to a right angle with the truck. 2: use a winch to suck the front of your vehicle down, disallowing the axle to pull away from the vehicle. Comp guys do both.

One of the more typical link suspensions for a crawler or daily driver is the Radius Arm system that you would find on something like an 80-series Land Cruiser. This suspension uses two lower arms that attach from the frame down to the axle. This arm at the axle attaches itself both above and below the axle?s centerline or in the case of an FJ80 front and back. These attachment points keep the axle from twisting under the vehicle. In addition to these two links a panhard bar is also used. It attaches from the driver side frame down to the passenger side axle again using misalignment joints and or bushings. Its duty is to keep the axle centered under the vehicle from lateral forces.

Traits: Due to the use of a panhard bar a lower roll center is typical of this type of suspension when used in the front. Oversteer is also a common trait among lifted vehicles. The IC is located by the placing of the lower links at the frame; therefore radius arm suspensions typically have very high AS numbers and are none adjustable.

Advantage: Provides a very good pinion angle through out its range of travel. Relatively easy to design/build and doesn?t have the complexity of the other systems.

Disadvantage: Steering suffers, in that the links don?t allow rotation of the axle in relation to the frame as the suspension cycles up and down, which cause caster changes. Wheel articulation is also limited due to link binding, a problem that is inherent with this system. One wheel pushes up and the other drops, which cause the links to twist the housing along its axis, much like a torsion bar. Options are limited in link placement making it inherently difficult to fine-tune Anti-Squat.

The Three-Link + Panhard, differs in only one area from the radius arm design. Here two lower links attach from the frame down to the axle housing. The third link attaches from higher up on the frame down to the axle housing. The upper and lowers are not typically parallel to each other, with more separation between them on the axle side than the frame. Like the radius arm system, it too uses a panhard bar to locate the axle from side to side.

Traits: Due to the use of a panhard bar a lower roll center is typical of this type of suspension. Oversteer is also a common trait among lifted vehicles.

Advantage: In relation to the frame this system allows for minimal caster change while suspension cycles. Desired anti-squat numbers are easier to attain, because the IC is located by two converging links instead of one. The three-link seems to have the least amount of binding, offering the most amount of wheel articulation for a system with a panhard bar.

Disadvantage: Pinion angles change due to the links rotating the housing during suspension travel. Playing with link lengths can minimize this.

The Four-Link + panhard bar which is also referred to as a ?Five-Link? by the OEM?s, uses two uppers, two lowers and a panhard bar. Unlike the three-link, which has the upper and lower converging at some point, the four-link?s upper and lowers are of equal length and parallel to each other. Without this key ingredient the four-link is a glorified version of the radius arm system.

Traits: Similar to the three-link and radius arm systems, it too has a lower roll center and a bit of oversteer.

Advantage: Because links are parallel and equal length steering angles stay consistent throughout wheel articulation.

Disadvantage: Pinion angle suffers when steering angles remain the same. Tying to place four links of equal length, which are parallel to each other can be a serious packaging problem. Long travel versions of this system only work if a spherical bearing is used at each end of each link, which gets expensive very quickly. Total of five links.

One of the more designer-friendly suspension systems. It consists of two upper and two lower links. One or both pair of links needs to be triangulated to make it work. No panhard bar is necessary. Typically speaking the upper links are triangulated. They mount above the differential close together and then separate as much as possible at the frame. The greater the angle these links have, the better the lateral control over the axle. Triangulating both will help even more. As a rule of thumb the uppers should be at least a 40-degree angle when viewed from above.

Traits: When the uppers are triangulated you get a higher roll center. When the lowers and uppers are triangulated you normally see a flatter roll axis.

Advantage: Wide-open design possibilities when used in the rear. If double triangulation is used understeer characteristics can be achieved. This is not to imply that you can?t attain understeer without it, but with a lifted vehicle you start to limit your options as to where you can put mounting brackets that won?t act like rock anchors.

Disadvantage: Packaging constraints. Just about every truck-based Toyota has their gas tank located beside the rear driveshaft. This design requires the relocation of the factory gas tank. Because of this many people choose to go with a panhard bar system in the rear.

Also called a wishbone suspension. Consists of one upper and two lower links. No panhard bar is necessary. With three attachment points this single link has two at the frame; one on either side and one at the axle housing forming a ?V? or wishbone, which acts as the necessary lateral support for this design. This design functions exactly like a triangulated four-link.

Traits: When the uppers are triangulated you get a higher roll center. When the lowers and uppers are triangulated you normally see a flatter roll axis.

Advantage: If double triangulation is used understeer characteristics can be achieved. This is not to imply that you can?t attain understeer without it, but with a lifted vehicle you start to limit your options as to where you can put mounting brackets that won?t act like rock anchors.

Disadvantage: Packaging constraints. This design requires the relocation of the factory gas tank. Typically less favored by designers, all of the torque loads from the upper links are transferred to one single point instead of the two, requiring much stronger link components and brackets.

With a Radius Arm, Three-Link+Panhard or Four-Link+Panhard it?s all the same. Your roll axis starts at the middle of your panhard bar, so the higher your panhard is from the ground the better, if a flat RA is desired. Of course this is difficult to do in the front because of the engine, so options will be limited. From there the axis either follows the same angle as the lower two links provided they are not triangulated or runs through the point at which the lower links converge on themselves when viewed from above. The flatter your lower links, the flatter or closer to a negative RA number you will be able to get. Don?t be surprised if in the end you can?t get a negative roll axis. It?s not easy with an oil pan.

With a triangulated four-link, things are almost the same. Instead of the panhard being what locates the axle portion of the axis, it?s the converging point of the two upper links. As with a panhard bar system this axis will mirror the angle of the lower links unless the lowers are also triangulated. Again flattening the lowers helps a lot with your roll axis.

When using a suspension system with a manual steering setup, the suspension must follow the arc or path of the drag Link in order to minimize bump steer. When viewed from the front, a system with a panhard travels in an arc relative to the length and angle of that link. It should be the same length and sit at the same angle as the drag link. If it doesn?t the panhard will push and pull the pitman arm changing the steering input at the wheel. It is highly recommended that if using a manual steering setup, a suspension with a panhard be used. The panhard is a perfect fit for a drag link, it can be built to mimic the length and angle of the drag link and by doing so minimize any bump steer. It also makes for a system that is reliable, predictable and safe to drive in any condition whether it?s street, Baja or crawlin?.

With a triangulated four-link front end, it is highly recommended that you use full-hydraulic steering. Also known as full hydro, it has no steering box or drag link only a tie-rod that attaches to a hydraulic ram. Because this suspension has no panhard it does not travel in an arch when viewed from the front. Instead it travels straight up and down. Remember a drag link needs to travel in an arc; a triangulated system doesn?t do that. If you combine conventional steering with a suspension like a triangulated four-link, the results would be drastic amounts of bump steer, to the point that it could be undriveable. However it is frowned upon to use a full hydraulic system while driving on the street. If a hose breaks, or the engine cuts out you are left with no steering and a dead stick, which is extremely dangerous on the street. Please don?t run full hydro on the street.

Don?t settle for, ?I put it there because everyone else did.?
  • You will get better street manners by minimizing your suspension?s oversteer.
  • Professional builders agree; flatter links perform better in ALL conditions. Example: Baja racers, CORR trucks, monster trucks, drag racers, stock car, OEM?s and competitive rock crawlers. This is one reason so many vehicles handle better with lower ride heights. The links flatten out.
  • Beware of those that claim they just tossed their links on and it all works great. What?s their definition of great? What yardstick are they using to measure success?
  • Flex is one of the easiest attributes to come by. Long links+spherical bearings+long shocks = lots ?o? flex. Don?t judge the performance of a linked suspension only by the amount of flex it has.
  • Anti-squat is something that has been debated much in recent years; it too is not the only attribute of a suspension system. Don?t get stuck on it, build adjustment into your design.

Rod Ends & Heim Joints

Updated: December 28, 2012

There are a lot of questions out there about Rod Ends / Heim Joints. What size to use, what mounting width, what tube adapter size etc. We have compiled a list of FAQ that we encounter and listed them on our site. I thought I would share the info for anyone who would like to read it.

Heim Joint Frequently Asked Questions :

Q: Where did the Heim Joint come from?
A: The Rod End was an amazing new component found on the high-tech control systems of a captured German fighter plane, shot down by the British, early in World War II. H.G. Heim Company was given an exclusive patent to manufacture the joints in North America. After the patent ran out, the name "Heim" stuck as a slang term.

Q: Where are Heim Joints used and why?
A: Heim Joints (Rod Ends) are used throughout the world. They offer easy mounting and adjustment of linkages and control rods. They are used in many different applications such as boats, doctor offices, fighter planes, the space shuttle and most importantly, monster trucks. Heim Joints are often one of the most overlooked necessities in a good build. In a truck world full of massive motors, unbreakable axles, huge tires, long travel nitrogen shocks, drop boxes and built transmissions, who cares about a Heim, right? The truth is, without the Heim you would be stuck on leaf springs, slowly driving over cars, not launching over bus stacks. The Heim is what allows all the crazy travel. If you break a Heim, it can break drive shafts, transmissions, bend shocks and cost you a heap of money. With all that being said there are so many things that are questionable. This article isn't going to regurgitate numbers and abbreviations that can be found on the net. It's just answering simple questions that have been asked time and time again but are never really answered.

Q: What exactly do you mean by "Load Ratings"?

A: (1) Axial Load - This is the force or load a joint can handle sideways. This is important when you are bouncing your rig off the side of the mud pits, have a hard side landing or a single shear application. This 1 ? " joint was put in a 250 ton press and the centre popped out of the body at 2000 lbs. (2) Radial Load - This is the force a Heim can take before it tears apart. Tensile is the point of failure. Yield is the point in which it deforms. It is important to use the yield numbers as a safety factor, since this is the point the joint becomes junk. (3) You can see the race and ball assembly poking out the side of the body. This is rare and the press test was a bit over the top. However, there are joints that can handle 25,000 lbs + in the same test. An average radial load rating for a 1 1/4" joint is around 40,000 lbs reaching up to 75,000 lbs. New hybrid joints have reached up to 130-140,000 lbs. At this point, the bolt holding the joint to the mount becomes the weak point.

Q: How do I know how much thread engagement I need?

(4) Thread Engagement - The strongest joint in the world is no good if it isn't threaded correctly. Standard practice is 1.5 times the depth of the diameter of the shank. For example, if the threaded shank of the joint is 1 ?", you need a minimum of 1 7/8 " threaded into your link. A higher-end joint made from chromoly will allow a thread depth of 1 times the diameter. There is zero, minimum, mid and full engagement. The goal is midway engagement, allowing maximum adjustment in and out. Since the shank is only as strong as 1.5 times its diameter, 100 percent engagement isn't necessary, nor is it stronger.

Q: I've tried welding my tube insert in and now the joint doesn't fit! How do I properly weld in a tube insert?
A: Be gentle. You don't have to pour the heat to it .The first thing welders do is turn the heat up for penetration. This is not a pipeline, a D-10 cat nor a lifting lug. It's a suspension joint that ultimately connects to a 1/8 thick piece of frame. It's normally 1018 cold roll so it welds nice. A ? inch chamfer and single pass all the way around the tube works well. On average a single weld 1 inch long can hold up to 60 000 pounds. Do not weld it with the joint stem in the insert. It doesn't prevent distortion. Do not thread the stem in until it's cold. Let it cool naturally. No dunking it in water. Once it's welded and cool, apply anti seize and thread the stem in gently. If it jams do not force it. Stop, back it out a half turn and try again. If it becomes jammed again DO NOT FORCE IT. Take a hammer and tap the end of the joint. Proceed with the clockwise/counter clockwise motion smacking the end with the hammer as you turn. Any further issues call someone that's more patient than you to do it. If the joint becomes so jammed that it cannot be removed simply zip disc the insert. Cut in until you see the tip of the threads, take a chisel and separate the grind slot. Proceed to turn the rod out. It's way cheaper replacing the insert than the joint.

Q: What sizes of joints are there?

A: (5) Joint Sizes - When it comes to sizes, generally the shank size matches the hole size. In the past, the joints were intended for more of a push/pull application with slight misalignment. This worked great, the stud and fastening bolt were equal in strength. Today there is a call for greater misalignment and the constant, heavy side-impact delivered to a trucks link create a need for a shank 60% larger than the bolt . In Image 5, the smallest Heim Joint is a 1 ?" x 1" standard rod end . The other joints range from 1 ?" up to 2" all with high misalignment balls. Unlike the standard rod end, the other joints through-holes are 60% the size of the stems. This allows for maximum strength with a deflection of 25 degrees. These are the newer hybrids. The two center ones are missing the balls. These types of joints have interchangeable internals.

Q: What does TPI Mean?
A: TPI stands for "Threads Per Inch. Threads on a joint are fairly standard. ANSI Class 2B. The most common sizes are ?" 16 TPI, 7/8" 14 TPI, 1" 14 TPI and 1 ?" 12 TPI. When you're trying to order a tap or jam nut and someone asks the thread pitch this is what they are talking about.

Q: How do I know where to place my mounts or how wide of a Heim Joint I need to fit inside my existing mounts?

A: (6 ) Mounting Width - When the shank of a joint snaps clean in two, it is often shrugged off as poor quality of steel or casting. If you look deeper, the cause of a clean break becomes clear. If a mount is allowed to come in contact with the body of a joint, it will bend it. As it twists the body sideways, all the force is placed at the top of the threads. This area is a stress point and it will snap a joint in the blink of an eye. When placing your mounts, make sure there is enough clearance between the mount and the joint at full misalignment. In figure 6, the red arrows indicate trace marks where the mount dug into the top and bottom on opposing sides. The mount on the top left indicates ones that are too close together and mounts on the top right are just right. Any tighter is too tight and any wider, the bolt will bend too easily.

Q: What are Misalignment spacers and what are they used for?

A: (7) Misalignment Spacers - These are used for more misalignment than the manufactured joint will allow. It does this by decreasing the size of the bolt hole in the ball. What the spacer does is take the ball and continue its radius. The same misalignment is achieved with a ball that already has a smaller hole. (ie: if a joint has a 1" bolt hole and you use "high misalignment" spacers, they will reduce the hole size to ?", ?" etc. By using the smaller bolt, it gives you more misalignment because of the extra clearance between edge of the bolt and the lip of the race. The down side to the spacer is that it has a seam, which allows dirt and grit to be carried into the race while high misalignment is being achieved. A ball with the spacers machined right on is another option to eliminate this problem and to sometimes achieve even better deflection rates.

Q: How do you know when to use right and left joints?
A: The whole point behind the cash spent on Heim Joints, threaded links and mount tabs is adjustability. A suspension link is a turnbuckle. Using left and right-hand threads allows you to increase or decrease the length of your link simply by turning it clockwise or counter clockwise. I've heard 100 reasons why guys want to run all right-handed joints. The only one that makes sense is less spare parts. Really, if you had to choose between setting your pinion angle by the simple twist of a link or spending hours unbolting and re-bolting your suspension just to save a few bucks, wouldn't you choose to run left and right joints?

Q: Do I really need to use a Jam Nut? What is their purpose?
A: Jam Nuts - If you don't use these you're wrecking your joint and link. The jam nuts job is to stretch the shank, pulling both the Inner diameter and outer diameter threads into each other and eliminating all movement and slop. All too often you'll see a rig missing these. It's a ticking time bomb. Some people will weld their jam nuts so they won't come loose. This defeats the purpose of the jam nut pressing the threads together. It will create interference but it won't be stretching the threads as required. As well you should use proper jam nuts. The machined face allows better surface contact helping the nut lock.

4 Link Suspension

Last Updated on: December 28, 2012

What is a 4 link suspension?
The four-link rear suspension is designed to locate the rear axle with four links, two on each side. Besides these links controlling and transmitting the loads placed on the axle during acceleration and braking, the bottom links also control the axle placement front to rear. The upper links keep the axle from rotating and keeps the pinion angle consistent.

A 4-link uses a Panhard bar or Watt's link (also used on other rear suspension set-ups) to laterally locate the rear end. The Panhard rod is used on many production vehicles that use a solid rear axle because it's simple yet effective, although a Watt's link is considered to be more adjustable/tunable than a Panhard bar.

A 4-link suspension can give an adjustable ride height, an adjustable roll center, and offers a nearly infinite number of possible adjustments that allow the chassis to be fine tuned. There is a lot of latitude in the basic design of a 4-link suspension to provide the desired road handling characteristics that will compliment most any driving style. A 4-link suspension can give a supple ride as opposed to ladder bars, which can be rather harsh on the street and a 4-link can even rival a leaf spring suspension for smoothness, while eliminating traction reducing wheel hop.

What types of 4 link suspensions are there?
Basically there are two main types: parallel and triangulated.:
Parallel 4-link
Laid out as it would be installed on the axle housings. Note the two pairs of links, the coil-over shocks and their mounts, and the Panhard bar in the rear

triangulated 4-link
Another design is the triangulated 4-link, one version seen above. In this design the upper links angle inward from the frame rails to the center section and serve to locate the rear end housing laterally so a Panhard bar or Watt's link is not needed. The lack of a Panhard bar or Watt's link can offer more clearance for the exhaust system or a fuel tank, etc., and generally looks cleaner/less cluttered.

The triangulated 4-link has been used by the OM's (Fox platform Fords and 1978-'88 GM G-bodies to name two) as well as sold in the after market by several vendors. While it has its advantages of a simpler, less cluttered look, one downside to it is called "roll bind". This is where there is a heavy lateral corning force applied to the rear end that basically binds up the action of the suspension. This can be controlled by using strong, high quality Heim joints and/or urethane bushings that have much less deflection, instead of the OEM-type rubber bushings.

Here is a 4 link calculator tool. You will need Microsoft Excell (or similar) in order to open/use it. 4 Link calculator

What does a driver wear when in a monster truck?

Last Updated on: March 28, 2008

Fire Resistant Suit, Shoes and Gloves - A Multi-layer fire retardant safety suits with a SFI rating of 3-2A/15 and shoes and gloves with a SFI rating of 3.3/5 are required.

Racing Helmet - All drivers an SFI 31.1 full or open face helmet, or SFI 31.2A (Snell SA) rated full-face helmet or SFI 31.1A (Snell SA) rated open-face helmet. (SA = Special Application Nomex lining Competition Helmet), SA2000 SNELL rated helmet are also legal. Also recommended are helmet restraints such as the HANS Device that integrate with the helmets.

What size tires do Monster Trucks use?

Last Updated on: April 16, 2008

Monster Truck tires are 66" tall, 43" wide and use a 25" rim are are universaly known as Terra tires or floation tires. Teams normaly inflate the tires between 8-14 PSI. They come in 6ply, 8ply & 10ply. Tires are manufactured by both Goodyear and Firestone. The tires were originaly developed for agricultural use and not intended for racing. Since these tires were not meant for racing, they are extremely heavy. For a race truck, these tires have tread shaved off them to make them lighter, even so a tire and rim still weighs around 700 pounds. There are newly released tires by Sudden Impact Racing which are much lighter and purpose made for racing.

What are the axles a monster truck uses?

Last Updated on: April 16, 2008

There are various axles used through out the monster truck indutry. Older monster trucks used standard Rockwell 2.5 ton and 5 ton "top loader" axles. Later they started modifying these axles and putting planetary gear sets on the ends. Today the most common type of axle today is the Rockwell F-106. Common planetaries used on these axles include the Clark 20 Ton, Rockwell PS-115, PS-250, and Pettibone. As of late, people have started using custom made "sheet metal" housings that use the Rockwell F-106 differential and normal planetaries, but it is a stronger housing. Instead of modifying axles to use planetaries, a few people have used complete axles that come with planetaries already attached. Some of these are the ZF APL365, APL765, and the previously mentioned PS115.

The planetaries are the wheel hubs of most monster trucks! A Planetary drive will have a input shaft entering one side with a gear (called a sun gear) on the `inside the hub' end. Three stationary `planet' gears will engage this `sun' gear and inturn engage a ring gear fastened to the outside case that transfers the shaft torque through the planet gears and on to the ring gear. The ring gear is fastened to the hub and the hub mounts the wheel and tire. Monster truck Planetaries provide a bigger bearing surface and much more `meat' (metal mass) than a standard hub and bearing like a school bus rear axle would have. There is also a gear reduction since the planet gears, the sun gear and the outer ring can be different sizes (well, effective size on the outer ring gear). On a monster truck, the planetary also incorporates the steering knuckle and Universal joint that allows the wheels to turn and steer the vehicle.

How does a monster truck turn?

Last Updated on: May 21, 2008

Unlike any other race vehicle in the world a monster truck uses a hydraulic orbital steering system with a check valve system. This means there is no mechanical link between the axle and steering wheel negating any "feed back". Not having feed back however is a good thing as with the amount of weight being turned, if it was to "kick" it would easily break fingers or wrists.

The rear steering system uses an electric over hydraulic motor along with a a self-centering function. The self centering function can be turned either on or off as well from within the cab.

What kind of transmission does a monster truck use?

Last Updated on: March 28, 2008

Monster trucks use automatic transmissions that are modified to be stronger and have manual valve bodies. A manual valve body means that you can shift through gears like a manual transmission, but not have to use a clutch. The types of transmissions commonly used are Turbo 400, Power Glide, C6 and Lenco.

What kind of transfer case does a monster truck use?

Last Updated on: May 21, 2008

Most "race" trucks today utilize gear driven transfer cases made by Profab or SCS Gear Box. These transfer cases allow you to change gear ratios relatively quickly to meet track condistions.

There are a few trucks however that are also ustilizing custom chain drives.

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