This article is part of a section of the RcTek site devoted to radio controlled model car handling. As car handling is an extremely complex subject, it will be quite some time before it is finished.
This article explains the various different ways in which caster angles can be adjusted and one of the side effects such adjustment can have on your model car. This article concentrates only on the front end of a model cars, as this is the end of the car that is predominantly adjustable for caster.
To adjust the caster angle on a model car, the lateral relationship between the bottom and top pivots of the axle block needs to be altered.
This is usually done by adjusting the top wishbone (A-arm), although it can be done by adjusting both.
The image on the right shows the basic parts for a front suspension assembly in which the caster adjusters are coloured green.
Caster angles can be adjusted in a number of different ways, but they fall into two distinct categories.
The first is shown in the image on the left and works by using a grub screw to lock the wishbone to the pivot pin.
This method is mostly suitable for alloy wishbones due to the need for enough strength in the threads to retain the forces generated in remote controlled car racing.
The second category of caster angle adjusters does not involve locking the wishbone to the pivot pin. By far the most popular of this method are the plastic mouldings shown left and right, which offer maximum convenience and light weight.
The alternatives to the clip on caster adjusters are the slide on spacer shown on the left, which can made from either plastic or metal. Whilst not offering the convenience of the above they do have the advantage of being very hard to displace in race accidents. The method shown to the right is seldom used as it hampers rapid adjustment, but uses an e-clip fitted into a groove in the pivot pin to retain the wishbone.
Although there are other side effects of adjusting caster, the method decided by the manufacturer can have an impact of the distance between the front and rear wheels (wheelbase) of the car.
In the image above the caster has been adjusted by repositioning both the top and bottom wishbones by equal amounts (in different directions). Because of this the centre line of the wheel is unaffected as it is the pivot point of the assembly. The wheel has not moved so the wheelbase remains unchanged.
The image above shows a car on which the caster has been adjusted by repositioning only the top wishbone. Because of this the centre line of the wheel axle changes due to the bottom wishbone becoming the pivot point. This moves the wheel backwards and shortens the wheelbase.