a. Rear suspension designs and applications are constantly evolving. Although the intent of the rear suspension rules are an attempt to accommodate the majority of suspension and suspension component designs and applications currently being used in competition, the rules cannot be absolute. Any and all new designs or modifications to an existing suspension and/or suspension component must be communicated to and approved by the Series Director before being used in competition.
b. Rear suspension must utilize either coil or leaf springs.
c. Rear suspension configuration used on current and new chassis(s) must be the design commonly known as four (4) link. Older cars currently competing with other rear suspension designs will be allowed to compete until further notification at the discretion of the Series Director.
d. In regard to swing arm and/or Z-Link suspension, these suspension types are permitted. The shock on a swing arm or z-link rear suspension may mount to the bird cage or bottom radius rod. Top and bottom solid links must be mounted on hiems and run in the opposite direction of the bird cage.
e. Bump sticks are not allowed anywhere on the car.
B. Front Suspension
a. All cars must utilize independent front coil spring suspension consisting of (1) one right and (1) one left lower control arm, (1) one right and (1) one left upper control arm, (1) right and (1) one left spindle, (1) one right and (1) left shock, and (1) one right and (1) one left spring / spring stack.
i. Lower control arms must be fabricated using magnetic mild steel or 4130 chrome moly tubing.
ii. Lower control arms may be of the “A” frame design with (2) two inner pivots or the Ford design with (1) one inner pivot and a strut rod to secure the control arm fore and aft movement. The strut rod may be mounted either forward or rearward of the control arm.
iii. All lower control arm frame mounts must be welded to the applicable frame rail. (The right lower control arm mounts must be welded to the right side frame rail and the left lower control arm mounts must be welded to the left side frame rail.) This procedure applies to the Ford style including the strut rod as well.
iv. Lower control arm mounts, (inner pivot points) must remain to the outside of the front frame centerline for the respective side.
v. The frame mounts for the lower control arm inner pivots may be adjustable by (2) two methods
1. A series of single round holes
2. A machined slot that will accept a steel “slug” with a single round mounting hole(s).
vi. Both methods of mounting must produce a secure non-moveable mount when assembled and tightened.
vii. Upper control arms must be fabricated using magnetic mild steel or 4130 chrome moly tubing.
viii. Upper control arms may be either the “A” frame type design with or without a shaft or the individual tube type with individual inner pivot mounts.
ix. All upper control arm frame mounts must be welded to the applicable frame rail. (The right upper control arm mounts must be welded to the right side frame rail and the left upper control arm mounts must be welded to the left side frame rail.)
x. The frame mounts for the upper control arm inner pivots may be adjustable by optional methods including but not limited to:
1. A series of single round holes
2. A machined slot that will accept a steel “slug” with a single round mounting hole(s).
3. A machined slot with a capture eccentric (cam) type adjuster
xi. All methods of mounting must produce a secure non-moveable mount when assembled and tightened.
xii. Spindles must be fabricated or forged using magnetic mild steel.
xiii. If separate, spindle steering arms must be welded to the spindle.
xiv. Steering arms must remain below the spindle pin.
xv. Spindles must connect to the upper and the lower control arms by utilizing ball joints, mono-balls, or spherical rod ends.
C. Axle Housing, Rear Differential
a. The axle housing must be of the “closed tube” design utilizing “full floating” magnetic steel axle shafts.
b. The center section of the axle housing must be manufactured of either aluminum or magnesium.
c. Axle tubes must be one (1) piece. Axle tubes must be manufactured of aluminum or magnetic mild steel. Axle tubes manufactured of exotic, heavy materials will not be permitted. The outside diameter of the axle tubes must not exceed three (3) inches. Axle tube internal inserts or external sleeves will not be permitted. The addition of any ballast weight to the axle housing will not be permitted.
d. Axle tube, including axle tube sleeves, donuts, or added parts may not exceed (3) three inches O.D. (outside diameter) at any point from center section to hub.
D. Rear Suspension Frame Mounts
a. The frame/roll cage structure must have integral welded mounting brackets for the attachment of rear suspension components. Frame suspension mounts may be welded or bolted securely (without any movement) to the frame/roll cage structure.
b. The only materials used to fabricate frame suspension mounts that will be permitted are magnetic steel or aluminum.
c. Frame suspension mounts may be either a single or double shear configuration for mounting suspension components.
d. Single shear frame suspension mounts must be a minimum of 1/4 inch in thickness. Double shear frame suspension mounts must be a minimum of 3/16-inch thickness on both sides of the mount.
e. All frame suspension mount component mounting holes must be round and sized correctly for the fastener being used. Clearance between the fastener and the mounting hole must not exceed the next fractional drill size. Example: 1/2-inch fastener, 33/64-inch mounting hole.
E. Axle Housing Mounts
a. Only one (1) axle-housing mount per side will be permitted.
b. The only materials used to fabricate axle housing mounts (birdcages) that will be permitted is aluminum or magnetic mild steel. Axle housing mounts fabricated of exotic, heavy materials will not be permitted.
c. When fabricating axle housing mounts, detail must be paid to functionality. The completed axle housing mounts, when comparing the right and the left side, must be as similar in design as possible.
d. Axle housing mounts may be a solid (welded) type or a floating type (birdcage) design.
e. The final assembled axle-housing mount must be a one (1)-piece mount. When a floating type mount (birdcage) is fabricated using two (2) pieces, the two (2) pieces must create a common one (1)-piece pivot (barrel). The two (2) pieces must be fastened or welded together to prevent independent movement of the two (2) pieces. The axle-housing mount must attach directly to the axle tube with clearance only to permit rotation of the entire mount. Fore, aft or vertical movement of the mount or the axle housing within the mount will not be permitted.
f. Mounts for suspension attaching (radius) rods must be an integral part of the axle-housing mount. The mounts may be either a single or double shear configuration. When using a single shear configuration, a minimum thickness of 1/4 inch for magnetic steel or 1/2 inch for aluminum is required. When using a double shear configuration, a minimum thickness of 3/16 inch for magnetic steel or 1/4 inch for aluminum is required. Dynamic movement of any mount other than a rotating and pivoting movement as a result of suspension travel will not be permitted.
g. Unless otherwise authorized by the Series Director, the mounting of any component(s) other than suspension attaching (radius) rods or shocks will not be permitted on the axle housing mounts.
F. Rear Suspension Attaching (Radius) Rods
a. A maximum of two (2) attaching (radius) rods per side will be permitted.
b. The only materials used to fabricate attaching (radius) rods that will be permitted are magnetic steel or aluminum
c. Attaching (radius) rods may be solid or tubular material. The material may be round or hexagon in shape.
d. Spherical rod ends, or steel clevises must be used at the end of each rod for pivoting, static length adjustment, and mounting. Bushings of any type will not be permitted.
e. The final assembled attaching (radius) rod must not have the capability to change length dynamically by any means or devices.
f. Spherical rod end sizes may be a minimum of a 5/8-inch rod end body with a 1/2-inch bearing to a maximum of a 3/4-inch rod end body with a 3/4-inch bearing.
g. In all applications, the correct size fastener must be used when mounting the spherical rod end to a bracket (example: 1/2-inch fastener must be used with a 1/2-inch bearing and mounting hole). Metal step spacers will be permitted to reduce the hole size of the spherical rod end bearing.
h. Attaching (radius) rods must mount directly to the frame suspension mount at the forward end and to the axle-housing mount at the rearward end.
i. All rear suspension fasteners must be magnetic steel with a minimum diameter of 1/2 inch. The use of grade 8 fasteners is highly recommended. All fasteners must be correctly sized for the component and application of use.
j. When rear suspension assembly is completed, the attaching (radius) rods must have a minimum of eight (8) inches between the pivots at both the frame suspension mount and the rear axle-housing mount.
G. Rear Travel Limiter (does not apply to DIRTcar sanctioned events)
a. A vertical travel limiting chain must be installed on the left rear of the car from the left rear axle housing to the frame. The travel limiting chain must attach to a clamp bracket (bearing type mount recommended) on the left rear axle tube between the birdcage and the edge of the left rear bell of the axle housing, and to the left rear frame directly above the chain mount on the rear axle. Must be mounted straight up and down. Travel limiting chains must be installed so that when taunt they are as close to vertical as possible. One compliance device may be used. The compliance device must not be more than (1) one inch thick (without a load applied) and remain completely open and visible. Compliance devices can be rubber or any like material but must not be installed in any type of a canister. Springs, spring loaded, and/or pneumatic devices will not be permitted. No tapered, beveled or roller skate style of compliance rubber will be allowed. Must be solid material, same diameter top to bottom, not hollowed or drilled to soften material.
b. The travel limiting chain including the compliance rubber must be installed so that when the car is jacked up from the rear the chain assembly is tight (no slack). The travel limiting chain is subject to inspection at any time during the Event at the discretion of the Officials, including but not limited to, qualifying, heat races, Last Chance Showdowns and the Feature. For inspection purposes the left rear tire pressure will be adjusted to (6) six psi. Cars will be jacked up on the under-slung frame rail between the center of the rear axle and the Panhard bar mount. The left rear under-slung rail must be located between the left rear birdcage and the edge of the left rear axle housing bell. If a chassis is not of the under-slung design, then the car will be jacked up on the left rear frame rail closest to the Panhard bar mount. Cars will be jacked up until a .040-inch shim will slide between the left rear tire and the ground. Once the car is jacked up as described a vertical measurement will be taken from the ground to top trailing edge of the rear deck bar, (6) six inches inboard of the left rear quarter panel outer edge. The measurement must not exceed 50-1/2 inches. (Cars without a left rear underslung must not exceed 49 ½”-inches
c. Penalties for failing this rule:
i. These penalties will be enforced on all Qualifying, Heats, Preliminary and Feature events:
1. 1/16”-inch – 1”-inch (50 9/16”-inch to 51 1/2″-inch) – Post qualifying penalty will result in 1 row penalty in the heat race. Heat, LCS & Feature penalty will be 3 positions in that event.
2. 1 1/16”-inch -2”-inch (51 9/16”-inch – 52 1/2″-inch) – Post qualifying penalty will result in a 2 row penalty in the heat race. Heat, LCS & Feature penalty will be 5 positions in that event.
3. Over 2 1/16”-inch (52 9/16”-inch and over) Post qualifying penalty will result in the driver tagging the tail of the heat race. Heat, LCS & Feature penalty will be being scored last in the event.
4. Any post qualifying penalty will result include the car and driver not being eligible for the feature redraw.
H. Torque Control Devices
a. Lift arm assemblies and pull bars will be permitted.
b. Only one (1) torque control device may be used.
c. Lift arms must attach to the axle housing using a mounting configuration that prevents any movement between the lift arm and the rear axle housing. A gusset or brace bar to prohibit side-to-side flex will be permitted.
d. The forward end of the lift arm may use a spring over shock assembly (5th coil), a spring or bushing, and a limiting chain.
e. Pull bars may be adjustable on both ends; however, the adjustments must remain fixed during competition. Adjustors within reach of the driver will not be permitted. No hydraulic or pneumatic pull bars will be permitted.
a. The front suspension must use magnetic steel coil springs
b. The rear suspension may use coil or leaf springs. The coil springs must be magnetic steel. Leaf springs may be either magnetic steel or a composite material
c. Coil springs may be used individually or stacked.
J. Shock Absorbers
a. Shocks are intended to dampen and help control spring frequencies in both the compression and rebound motions. The amount of force applied to move the shock piston and shaft assembly may be varied with the option of shock “builds” however the piston and shaft assembly must have the ability to move in both directions.
b. Mono-tube, single piston, nitrogen gas charged shocks will be permitted. All shocks must utilize mechanical oil controls, such as: spring shim(s), drum and disc(s), check ball and spring, needle and seat for internal and external shock adjustments. Magnetic and/or electro-magnetic controls are not permitted. Remote nitrogen gas reservoirs will be permitted. The remote reservoirs may contain a compression adjustor. Adjustments described above are the only shock adjustments that will be permitted.
c. Shock adjustments while the vehicle is in motion will not be permitted.
d. Shocks and shock components may only be manufactured from steel or aluminum.
e. Rotating parts will not be permitted inside or mounted to the shock absorber. Inertia/gyro style shocks are not permitted.
f. Thru-rod shocks will not be permitted.
g. Unless otherwise authorized, all shocks must be mounted as close to vertical as possible.
h. Approved shock locations are as follows:
i. One (1) shock will be permitted at each front wheel
ii. One (1) shock will be permitted at the right rear wheel
iii. Two (2) shocks will be permitted at the left rear wheel. When using only one (1) shock at the left rear wheel, the shock must be mounted behind the rear axle tube. When two (2) shocks are used at the left rear wheel, one (1) shock must be mounted behind the rear axle tube and the second shock must be mounted on top of or forward of the rear axle tube.
iv. One (1) shock will be permitted mid-ship at the front of the lift arm assembly.
v. One (1) braking shock will be permitted. The shock must be mounted within three (3) inches of the center line of the rear axle center section. This shock must be mounted horizontally.
i. Prior to introduction into competition a new design shock absorber must be submitted to World Racing Group / World of Outlaws Morton Buildings Officials for approval. Shock absorber manufacturers may be required to provide a board of components for inspection and display.
j. Air shocks are permitted.