Scrub Radius on a Dune Buggy

April 30, 2023 0 Comments

The scrub radius is a distance between the lean of the steer axle and the center of the wheel where, theoretically, both would touch the road. The steering axis is a line between the lower ball joint and the upper kingpin 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 placed where the strut connects the control arms. Steer axis tilt could be measured as the angle between the center line and the steer 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 might allow you to drive the car safely.

If the center line is in then the radius of friction is positive and if it is outside the center line of the tire then the radius of friction is negative. Most rear wheel drive trucks and cars have a positive roll radius and FWD cars have a negative or zero roll radius as they have a higher level SAI angle. To alter the scrub radius, the use of wheels that have a different offset than the original may 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 performing a positive offset LESS is poor steering control that develops a visible tramline coating on surfaces. The wheels would come off either side, encouraging instability at high speed. 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 automobiles. This is the main reason why many of the 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 just like the wheels, which reduces efforts when parking the car. This also helps to increase the width of the engine bay, which is quite an important point in most sports cars. Scrub radius is very important when it comes to steering stability and wheel alignment. In the case of a small scrubbing radius, the contact patch would rotate in place while parking the vehicle and would require a lot of effort. One advantage of the scrub radius is that the small scrub radius allows the steering to become a bit less sensitive to braking inputs, in particular.

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