Rear suspensions don’t come...
Rear suspensions don’t come more traditional than a Model A spring and a quick-change centersection. The ladder bars, shocks, and rear spring come from Pete & Jakes.
Satchel Links behave much like a triangulated four-bar, but can sometimes provide a lower roll center. This will require a larger sway bar to control body roll. Otherwise, packaging a Satchel link is like a Tri-four-bar—very good, but the underside layout of the car will determine which suspension fits best.
Three-links have a tendency to be geared toward performance applications because the minimal amount of links lets the axle roll very freely and allows the sway bar to do all the work of controlling body roll instead of relying on bushing compliance.
Roll steering can be very good while still delivering a high amount of antisquat, which provides excellent stability when entering a high speed corner, and allows good forward traction on corner exit.
A Model A chassis with its...
A Model A chassis with its high arch rear transverse spring exhibits a roll axis with an exaggerated slope. As a result going around a sharp corner unloads the inside rear tire.
These suspensions are easier to add adjustability into the design as well. The biggest downside is packaging; the placement of the upper link can often determine if a rear seat is even possible. The chassis mounting point for the upper link must be very strong because it is the only link under tension while on the throttle, while four-link/bar suspensions have two links to carry the load. Also, any three-link will require a device to limit lateral movement, such as a Panhard bar or a watts link.
Four-links are the ultimate way to provide high traction, high adjustability, and high strength at the expense of everything else. These suspensions often require major floor and trunk modifications to fit, and have a tendency to high amounts of roll bind, which can make the suspension feel harsh in a one-wheel bump.
An alternative to the Panhard...
An alternative to the Panhard bar is the Watts link. AME offers them as an option on some suspension systems.
Ladder bars can provide great traction, great packaging, and ease of use at the expense of street driving manners. They are very easy to set up because adjustment is somewhat limited (compared to a drag-race–style four-link), but are simple and effective.
The downside is body roll causes a high degree of bind, which can place a lot of stress on the chassis brackets where the ladder bars attach. Also, because of the bind, one-wheel bumps will feel harsh.
Truck arms rely on their own deflection and bushing stiffness to work well in cars, and must be properly designed. If they are too light, they can create drivetrain harmonics and greatly increase vibration. If they are built too heavy they will unnecessarily increase unsprung weight above and beyond the high amount of unsprung weight they already have. This high unsprung weight needs to be controlled by high spring rates, which further decreases ride quality.
This Watts link from an Australian...
This Watts link from an Australian Ford was adapted for use on the author’s ’34 Ford with parallel four-bars.
Street Rod Ladder Bars
Somewhat of a cross between drag race ladder bars and truck arms, these are generally made out of tubing to reduce weight and are gusseted to increase strength. They are normally anchored to the axle housing in such a manner that pinion angle is adjustable while the frame ends are mounted close together to reduce the binding inherent in the design.
If price is a big concern and the ability to tune ride quality is not, leaf springs can work reasonably well. They are unique in that they are a suspension member and spring all in one package.
Jerry Kugel, of Kugel Komponents,...
Jerry Kugel, of Kugel Komponents, designed this IRS for street rods. Available in a variety of widths, it has inboard disc brakes and a Winters quick-change centersection. Standard centersections with Ford 9-inch gears are also available.
Lateral stability can be good, and handling can be pretty good if the system is well designed. Downsides: Lack of adjustability to compensate for more or less weight and there can be some noise from inter-leaf friction. Another downside is roll stiffness ... imagine twisting a leaf spring—they are very stiff! This is why leaf sprung cars normally do not need sway bars (except trucks for hauling weight), as the rear roll stiffness can be so high, which increases oversteer.
Watts Links do a great job at locating the rear axle laterally. Up and down motion is almost perfectly vertical, and lateral stiffness is as good as any Panhard bar. The downside is complexity: they typically have twice as many parts (or more) as a typical Panhard bar. And because of the links, exhaust routing can be very difficult.
Heidt’s Surperide IRS comes...
Heidt’s Surperide IRS comes in tread widths from 55-62 inches, making it suitable for a variety of applications. A long list of options can be selected, including chrome control arms, half shafts, and uprights, as well as a variety of centersection options.
To be effective, the bar must be a long as possible to reduce side-to-side movement. As an example a 32-inch Panhard bar will allow the axle to move sideways 1/8 inch in 3 inches of bump travel. A 20-inch bar will allow the axle to move 1/4-inch in the same bump travel. These numbers aren’t a big deal for typical street cars, but “spirited” drivers might want something better (increasing Panhard bar length or using a Watts Link).
These are a simple way to control lateral movement of the axle. If designed right, lateral movement can be kept to a minimal throughout its travel, and exhaust routing is easier than compared to a Watts Link.
A diagonal link is an effective method of controlling side-to-side movement on drag cars but should not be considered for street use. The attachment points tend to work loose on the street, which can result in them failing and creating an unsafe situation.