Throughout the years, vehicle manufacturer’s have designed numerous types of suspension from independent control arms and twin traction beams, to leaf springs, radius arms, or multi-link. Each suspension style has its pros and cons to ride quality, durability, payload and ability to be modified, but have you ever thought about what determines “which type of suspension” a vehicle gets equipped with.
The question which typically determines this is: Did the factory choose to run a solid axle differential or not. If they did, then your vehicle is going to be equipped with leaf springs, radius arms, or a multi-link suspension. If they did not, then in most cases, your vehicle is going to be equipped with independent suspension.
A solid axle differential has been used since the creation of the motor vehicle and has proven to be a stout, reliable design to convert the rotation of the driveshaft running from front to back, to a rotation from left to right. A solid axle not only houses the differential, but it also houses the axles, wheel bearings and brakes all in one unit. Carried over from the horse and buggy days, most solid axle equipped vehicles utilize “leaf springs” for the suspension which not only hold up the weight of vehicle but also position the axle as it cycles through its range of motion. Leaf springs are a simple and reliable form of suspension which also work great when it comes to heavy payload, but do not offer the most comfortable ride quality. Due to this, manufacturers created ways to utilize a coil spring for the suspension which features a much smoother ride quality, but is not an “all-in-one” like its predecessor, the leaf spring, so other components were needed to control the axle as it cycles through the suspensions’ range of motion.
Radius arms or suspension links were created to hold and designate the path of a solid axle as it cycles through the suspension’s range of motion. Radius arms, which generally attach to the axle at two points and to the frame at one point, allow a solid axle to pivot up and down in a radius motion, but are not able to control side to side motion so a trac bar is also needed. Radius arms are strong and simple, but can also be know for creating an up & down “porpoise like” feeling as the suspension cycles and allow alignment aspects to change undesirably. This led to the more modern, “multi-link” style suspension which utilizes upper and lower control arms to designate the path of the axle along with a trac bar to control the side-to-side motion. These suspension links feature two pivot points on the frame and two on the axle, allowing the solid axle to cycle and pivot more naturally while with the correct geometry, also maintain alignment aspects as well as desirable driveline angles.
Following the development and implementation of coil spring suspension, OEM designers sought to further improve ride quality by completely separating the suspension side to side with the development of independent front suspension, better know as “IFS”. IFS suspension is typically comprised of upper and lower control arms that are connected in the middle by a steering knuckle which is able to pivot left to right when commanded by the driver of the vehicle. Independent suspension allowed for the isolation of vehicle’s reaction to a bump, meaning that if the vehicle hits a bump on the left side, the right side is not affected as it would have previously been with a solid axle. Next came the independent differential that allowed drive axles to be to be installed with independent suspension whether in the front as “IFS” or in the rear with “IRS”. Independent suspension has seemed to take over most modern platforms as it allows for a softer ride and tends to be less weight for better fuel efficiency. Solid axle equipped suspension is still very common, however, only in the rear of most trucks or front and rear of some 2500/3500 trucks for reasons of strength and weight carrying ability. It is also very popular in slower speed, off-road vehicles such as rock crawlers who tend to run a high level of torque through their driveline and place a lot of stress on their physical suspension components. High speed, offroad trucks tend to lean towards independent suspension for its’ smoother ride and isolated control of handling obstacles.
Both styles of suspension, whether solid axle or independent, are purpose built to best suit the intentions of the vehicle in which they are installed in. They both feature many pros and cons that can be best argued by the preference of the consumer so when it comes to your personal preference, know what you are buying and know what your intensions for the vehicle are.
