4-Bar Rear Suspension – Air Bags & Air Ride

Why Equal-Length Parallel 4-Bar Works So Well
With Air Suspension

Air suspension typically operates through a much larger range of ride heights than a conventional coilover suspension. That makes proper rear suspension geometry even more important. Scott’s Equal-Length Parallel 4-Bar uses upper and lower link bars of equal length positioned parallel to one another, allowing the rear axle to travel through the suspension range while maintaining a consistent relationship between the rear end and chassis.

For a bagged hot rod or custom truck that may transition from an extremely low parked height to normal driving height, predictable suspension movement is critical. Scott’s 4-Bar design provides a strong, simple and fully adjustable foundation engineered specifically for vehicles using air suspension.

Panhard Bar vs. Watt’s Link for Air Suspension

The standard Scott’s Airbag 4-Bar includes a heavy-duty adjustable Panhard bar. For many applications, a properly designed long Panhard bar provides excellent lateral axle control. Scott’s uses the longest practical Panhard bar possible to minimize lateral movement as the suspension travels.

However, a Panhard bar still moves through an arc. A Watt’s Link uses a centered pivot arrangement that allows the rear axle to remain centered beneath the chassis throughout suspension travel. That difference becomes especially valuable on air suspension vehicles because of their increased range of vertical movement.

For a traditional street-driven coilover vehicle, the Panhard bar is an excellent solution. For a SuperSlam airbag vehicle with substantial suspension travel, Scott’s strongly recommends considering the Watt’s Link.

That last distinction also helps prevent the coilover and airbag pages from competing with each other.

Slam Specialties Air Springs & RideTech Shocks

Scott’s Airbag 4-Bar combines Slam Specialties TS-6 tapered air springs with RideTech HQ single-adjustable shocks, allowing the spring and damping functions to be controlled independently.

The air springs provide the ride-height adjustment and suspension travel needed for an ultra-low stance, while the external RideTech shocks control suspension movement and damping. This is fundamentally different from simply installing airbags without properly matched shock control.

Whether the vehicle is cruising at normal ride height or sitting down at show height, the suspension is designed as an integrated system around the intended range of travel.

Step Notch for Maximum Airbag Suspension Travel

Getting a vehicle extremely low requires more than installing airbags. As the chassis is lowered, sufficient clearance must be provided for the rear axle to travel upward without contacting the frame.

Scott’s offers Step Notch options specifically for bagged vehicles, providing the additional axle clearance required for aggressive ride heights and increased suspension travel. The current system offers both single-bend and custom triple-bend Step Notch configurations.

When planning a vehicle intended to lay frame or sit extremely low, the air springs, shock travel, rear axle clearance, link geometry and lateral locating system should all be considered together from the beginning.

Airbag 4-Bar vs. Coilover 4-Bar: Which Is Right for Your Build?

Choose a Coilover 4-Bar when your priority is a fixed performance-oriented ride height, straightforward suspension tuning and excellent street or Pro Touring handling.

Choose the Airbag 4-Bar when adjustable ride height and an ultra-low stance are major goals of the build. The Scott’s Airbag system allows the vehicle to sit dramatically lower while still being raised to a proper driving height.

Both systems use Scott’s Equal-Length Parallel 4-Bar geometry and heavy-duty construction. The major difference is how the vehicle’s weight is supported and how much suspension travel the finished vehicle is expected to use.

Built for More Than Just Looking Low

A properly engineered air suspension needs to do more than make the vehicle look good when it’s parked. Scott’s builds its Airbag 4-Bar using the same heavy-duty construction standards found throughout our suspension and chassis systems.

The link bars and Panhard bar are manufactured from 1-1/8″ x .250-wall DOM tubing, with bars CNC machined in-house for consistent quality. CNC-machined stainless steel right- and left-hand threaded rod ends allow pinion-angle adjustment without removing the link bars, while FK Bearing Heim joints and 5/8″ Grade 8 hardware provide the strength required for serious street and performance applications.

Build Your Air Ride Suspension as a Complete System

Getting a hot rod, classic car or custom truck to sit on the ground is easy. Getting it to sit low and still drive, handle and function properly takes engineering. Scott’s Hotrods Airbag 4-Bar Rear Suspension is designed around the entire range of suspension travel, combining Equal-Length Parallel 4-Bar geometry, Slam Specialties air springs, RideTech shocks and heavy-duty adjustable components into a complete rear suspension system.

For builders who want the best rear axle control throughout that travel, Scott’s highly recommends adding our Watt’s Link—preferably paired with a Moser M9 FAB rear-end housing for the cleanest and most effective mounting configuration. Add the appropriate Step Notch for axle clearance, and you have a rear suspension package designed from the beginning around an ultra-low, air-suspended vehicle.

Whether you’re building a slammed street rod, bagged classic car, custom C10, F100 or one-off show vehicle, Scott’s can configure the rear suspension around your vehicle, your desired ride height and the way you intend to drive it.

Don’t just put your vehicle on air. Build the rear suspension to work correctly on air.