Jacking - RC Handling Guides

RC cars with upper and lower suspension links (or arms) undergo jacking forces in turns.

Jacking forces are the result of the outside tire (hopefully) getting grip on the track and resisting the movement of the car, forcing it to turn. The car's inertia pushes on the hub of the outer wheel, forcing the top of the wheel to lean outward as the grip it has on the track pulls it inwards, towards the chassis.

The inside tire and hub, conversely, are forced to lean inward as the car's inertia pulls the upper link inward towards the chassis and the track pulls the bottom of the tire outward, away from the chassis.

The combination of the outside hub leaning outward and the inside hub leaning inward creates the jacking force which will force the car's chassis to either lift or drop, depending on your suspension geometry, and specifically, your car's roll center.

When the jacking force pushes the car's chassis downward, it is referred to as being "in the track" (which is generally desirable.) If it pushes the car's chassis upwards, it is referred to as being "on the track" (generally undesirable.)

This can be a little confusing, and rather than going into the nitty gritty details, I'll include JQ's excellent explainer video on the topic:

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Note: jacking requires upper and lower suspension links to exist, so it does not happen in pan cars or other suspensions that have either a single solid axle (rear of a pan car) or that have only an upper or lower suspension arm that supports the hub (front of many pan cars.)