Front Suspension Details

Toe: This one is easy. Look down at your feet and think of them as tires. Toe in toe out. Yep, that covers that. Even though it is a good place to start the topic it is still the final adjustment made when you are finished fabricating. Toe is usually set after the first test drive by most builders that have gone the distance. Toe is a concern on the rear axle as well as the front. Set your toe at ride height. Even though bump steer can be worked out of the Panther front suspension many of you will press on, and tolerate the annoyance just to get some seat time. Set the toe with a measuring tape. Have someone help you hold the tape at the casting flash at the center of the tire. Casting flash is the seam left by the mold when making the tire. Measure the distance between the tires at center, both front and rear. Make sure the centerlines of the tires are 1/8" closer on the front side. Because bump steer and toe are somewhat related click on the image below and for more info on bump steer, and how to get rid of it.

Camber: Is the angle of the tires as viewed from the front of the kart. When you go to most places on the Internet to talk buggies Camber seems to be the favorite topic. It is important because it has a lot to do with the handling and predictability of the kart. Camber is sometimes traded for other features depending on the out come sought after by different fabricators. Camber counts at all four wheels also. Camber is described as positive or negative, Negative camber is when the top of the tire tips in towards the frame and positive camber is when the top of the tire tips away from the frame.

Kingpin inclination is the angle of the King Pin in relationship to the tire as the king pin and tire are viewed from the front. It is only tied to Camber when reference is made to the adjustment of the Camber. The effects of King Pin inclination can be affected by the size of the tire and the rim offset. The reason an angle of inclination is added to the spindle is so that the scrub radius of the tire turning can be eliminated or at least reduced. In the illustration you can see how the path of the contact patch can be controlled with a carefully designed spindle.

Scrub Radius: This can be described as the path that the front tire takes when the rail is static. Stopped. I don't design anything to be easy to push around the garage. However this test allows you to get a good look at how the trail is going to push back into the steering wheel. The whole front suspension is an integrated geometrical puzzle that can work for you or against you. If you can picture yourself driving for hours on the back road you need to consider your scrub radius in order to minimize the feed back from the wheel so you have a mechanical advantage over the elements.

Ackerman: This one could be debated forever. I'm certain that this is the low priority in off-road steering geometry. Ackerman is the angle of the steering arm in relation to the spindle. This is a crucial angle for pavement cars, but there are enough successful builders around with opposing viewpoints that I'm convinced there are a few good ways to do this. My approach has been to divide the rule of thumb for Ackerman in half. This gives me the opportunity to use a more affordable rim, maintain a proper off set, and still get the turning angle that I need for a cart with a spool.

Castor: Castor is the angle is the angle of the king pin as viewed from the side of the car. Having the castor angle tip to the back of the buggy a few degrees will make the buggy track straight. The more you tip the castor angle back the more the tire will lean into the turn and some say will give a better bite. I have done it and I like the effect. If you add too much castor it will make the steering a little heavy. This is seldom noticed because the kart is so light.

Approach Angle: This angle is not found in the Suspension Geometry books written for pavement cars. When an A-arm suspension is tipped back as a complete assembly a few degrees it allows the tires to move back and out of the way of the bump as the tire hits and rolls over the obstacle. Tilting the arms back is referred to by some as the approach angle. There are other respected teams that refer to the angle of the push bar as the approach angle. In the picture below you get a good look at the approach angle of the ATK. I some times feel that the angle is a bit much. However they handle real nice and the steering does not become heavy at slow speeds. The Castor angle is taken care of at the same time and the steering returns to zero when steering the wheel is released.

Scrub: A-arm scrub is the action of the tire moving laterally through the arch of the suspension travel. Scrub is impossible to eliminate in an A-arm suspension but can be held to a minimum. If the A-arm set up were going on an Indy car then the short wheel travel would make the scrub unnoticeable. Because wheel travel and ground clearance is the name of the game in off-road scrub is something worth taking a closer look at. If additional ground clearance were not important then a 25" A-arm with a 50 degree arch would only generate about 2.3" of scrub. However, when the angle is added to the end of the A-arms to get more droop the scrub increases.

Wheel offset: Is important in that it saves bearings and reduces feedback to the wheel. When you get the wheel properly wrapped around the axle it will tend to interfere with other steering actions, primarily the tie rods. Having the perfect rim offset may require you to buy the next larger diameter wheel and tire. I have always deferred to the less expensive as a trade-off for the perfect set up.