Scrub Radius in a Dune Buggy


The scrub radius is a distance between the tilt of the steering axis and the center of the wheel where, in theory, both would touch the road. The steering axis is a line between the lower ball joint and the upper pivot of the hub. On the McPherson strut, the upper pivot point is the strut bearing, while the lower point consists of the lower ball joint. Making use of the suspension using the lower and upper control arms, the pivot points are positioned where the strut connects the control arms. The tilt of the steering axis could be measured as the angle between the center line and the steering axis. This means that if the tilt is found to be adjustable at the pivot points, then the UPS can be changed. So altering the scrub radius by changing the width of the wheel offsets could allow you to drive the car safely.

If the centerline is on the inside then the radius of friction is positive and if it is off the centerline of the tire then the radius of friction is negative. Rear wheel drive trucks and cars mostly have a positive turning radius and FWD cars have a negative or zero turning radius as they have a higher level SAI angle. To alter the scrub radius, using wheels that have a different offset than the original could be helpful. The main purpose of the scrub radius is to help center the wheels after cornering and also to maintain wheel stability.

The net effect of running a positive offset LESS is poor steering control that develops a visible tram coating on surfaces. The wheels would come off on either side, promoting high-speed instability. Such types of effects could be reduced simply by placing the front wheel alignment in neutral. However, in many cases it would be unwise to use wheels that alter the scrubbing radius of cars. This is the main reason why many insurance companies do not pay for accidents involving cars with spare wheels.

Previously, on most cars, a larger scrub radius was used, four inches or maybe around 100mm. Its advantage is that the tire rolls like the wheels, which reduces efforts when parking the car. This also helps increase the width of the engine bay, which is a pretty big deal on most sports cars. The scrub radius is very important when it comes to steering stability and wheel alignment. In the case of a small scrub radius, the contact patch would rotate in place while parking the vehicle and require a lot of effort. An advantage of the scrub radius is that the small scrub radius allows the steering to become a little less sensitive to braking inputs, in particular.

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