The main chassis is complete and it is time to attach all the brackets. This can actually take more time than building the chassis assembly itself. Some of the most important brackets are the ones that attach the front suspension and steering. Our Morrison truck came with detailed blueprints highlighting all the dimensions for mounting the struts and steering rack. Our RPM Classified Project S-10 uses a pair of Morrison built MacPherson struts. These heavy duty struts attach to the chassis at three mounting points, two on the main frame rail and the third to a cup attached to the strut tube that runs from the dash bar to the front of the main frame rail. The strut uses a lower control arm or A-arm that consists of two tubes that attach to the strut with a ball joint at the strut end and Heim joints to the brackets on the main frame rail. These brackets are attached at two different vertical heights to in-build anti-dive into the front suspension. This helps stop the car diving forward and transferring weight to the front wheels during braking at the end of the dragstrip. This helps eliminate the chance of spinning the racecar under braking and getting into a nasty accident. The fact that the A – Arms are attached to the chassis using Heim joints allow the racer to set up the suspension to the specifications required for the speed to be run.

When Art Morrison lays out the front suspension on any racecar he has to take many important factors into consideration. Almost everyone has heard of camber, camber is not as important on a drag car as a road race or oval car but it has to be thought about during the setup of the suspension. Camber is the inclination of the front wheel when looking from the front or rear of the vehicle. You ideally want camber to be zero degrees and stay as close to that as possible during the run.

Caster is the angle of the front strut from the stub axle to the upper mount viewed from the side of the vehicle. The more caster, the more self-centering effect the steering has and therefore the straighter it will track on the racing surface. A regular road car has about 2 degrees of caster whereas some of the quicker racecars can run as much as 10 degrees.

The IHRA and NHRA allow you to offset the front struts to increase the rollout distance. Traditionally it is the left wheel that is moved forward to increase rollout as it is the wheel that tries to lift out of the beams first on the launch. The increased rollout really helps on a car that jerks the wheels out of the beams before moving forward.

An integral part of the front end is the steering. Morrison supplied the new Pinto rack and pinion along with mounting brackets for our truck. The blueprints give you the dimensions to pinpoint where the rack has to be mounted. Many racers have heard the term bump steer but are not really sure what it means. Bump Steer happens when the front suspension travels up or down and the rack tie rods arms travel in a different arc from the A-Arms therefore moving the wheels in or out during the suspension movement. This has potentially serious consequences, as the steering working independently of the driver during a run is the last thing you want. When looking at the front of the car you should see the A-Arms and tie rod arms parallel and able to swing in a common arc. It may not be feasible to totally remove bump steer but it has to be minimized and kept to a toe in condition if at all possible. Having the steering toe out during the run is not desirable as it makes the racecar highly unstable, especially at speed. Moving the tie rod arms to swing in the same arc can be done in a couple of ways. The first is to move the rack up or down until the rods are parallel or the other option is to fit spacers between the steering arm attached to the strut and the Heim joint on the steering arm to achieve the same effect.

Once the racecar is sitting on its wheels at ride height you want to check out your steering toe in. Ideally it should be set close to parallel without the chance of any remaining bump steer causing a toe out condition. Some people set this to 1/8’ toe in to ensure this does not happen. Excessive toe in will scrub off speed as you go down the racetrack due to the tires scrubbing as well as rolling. This is guaranteed to hurt your E.T. We use a neat laser aligning device built by Mach 3 Racing of Oakville, ON to align the front end of our truck. The device uses a laser pointer and four metal plates that are placed at the front and rear of the car. The pointer is directed towards the plate at the front, the red dot marked. The pointer is then rotated to the rear plate and the red dot again marked. The procedure is then reversed on the opposite side of the vehicle. A measurement is taken between the pair of dots at the front and the rear, then compared and it can be seen if the steering is in a toe in or out scenario. Make an adjustment and then go through the measuring process again until your steering toe in is properly set.

I hope this article has enlightened you on some of the intricacies of suspension and steering. If you are not sure about the settings required for your racecar make sure you contact a chassis builder who will be able to point you in the right direction. Remember it can be dangerous to have a racecar that will not steer down the racetrack in a straight line. Check it out, your life depends on it.

Mach 3 Racing
1252 Speers Road, Unit 4,
Oakville, ON, L6L 5N9
(905) 847-2616
www.mach3racing.com

SOURCES

Art Morrison Enterprises
5301 8th Street East Fife, WA 98424
(800) 929-7188
www.artmorrison.com

GTS Fiberglass
1675 W. Pearce Blvd, Wentzville, MO, 63385
(636) 639-6724
www.gtsfiberglass.com

HeadsUpRacer.com
Ian@headsupracer.com