Independent Rear Suspension

Motor Trike selected a Short Long Arm Suspension with H-Arm and Camber Link

Four major design criteria led Motor Trike's engineering team to create its current suspension:

1. Traction/Grip—increase camber gain and lower CG height
2. Ride Quality—optimize natural frequency and reduce NVH
3. Leaning/Sway Control—correct roll stiffness and balance anti roll bar with roll center height
4. Bump Steer/Stability—tire scrub, roll center height, and toe change
5. Install Time—reduce install time and get customers on the road

To make for better cornering and travel across various road conditions, Motor Trike increased the camber gain, improving the traction of the tires and how safely they maintain their grip on the road. The tire contact patch is kept flat to the road when it is important.

The picture depicts a severe corner with a lot of body roll. Notice that the outside tire is still flat to the road.

Our suspension was also designed to keep the inside tire on the ground, maximizing tire-to-road traction in the event of severe cornering. Motor Trike engineers accomplished this by lowering the center of gravity (CG) height, placing the heaviest components as low as possible.

This reduces load transfer to the outside tire, keeping both tires on the ground.

The smoothest of riding experiences means accounting for both various load situations and any number of road conditions. To accomplish this, Motor Trike optimized the natural frequency.

Natural frequency is a tool engineers use to measure the ride quality of a suspension. Every suspension has a frequency at which it will naturally oscillate. That frequency is based on spring rate and weight.

The optimum natural frequency that humans prefer is below 2.5 Hz. The lower it is, the more we like it. The challenge is to keep the spring rate as low as possible without running out of suspension travel.

Suspension travel is the gateway to ride quality. With over four inches of wheel travel, Motor Trike engineers were able to optimize the ride quality by lowering the spring rate and, therefore, the natural frequency. This is only possible if you have enough travel to accommodate the soft springs.

Our trikes are like pickup trucks: they are similar since we must accommodate large load variations and maintain ride quality at the same time.

We utilize air springs to adjust the spring rate and maintain ride height and natural frequency. This is how our trikes ride well, regardless if carrying one 120-pound rider or two 250-pound riders.

The last obstacle to optimizing ride quality as part of the IRS design was noise vibration and harshness (NVH). The source of NVH is any factor that creates noises and vibrations, such as the engine, brakes, gears, tires, and road irregularities. NVH is transmitted to the riders though the vehicle chassis.

Because it is impossible to eliminate the source of all NVH, Motor Trike created a barrier between NVH sources and riders. This barrier system is comprised of the rubber bushing mounted differential as well as rubber bushings for all suspension components—anti roll bar, shocks, suspension arms.

The correct roll (cornering) stiffness gives the rider comfort and feedback when maneuvering. This was why the amount of sway control greatly influenced our IRS design.

If the roll stiffness is too stiff, the rider becomes overconfident because the trike corners too flatly, removing any sense of danger. Ride quality can be ruined with just one wheel bump.

If the roll stiffness is too soft, the rider feels a false sense of doom. If the trike leans too much, the rider feels as if he/she is going to tip over or slide out of control.

Roll center height is also important because it controls many suspension parameters including the “lever arm” that causes body roll. The roll center can be thought of as the pivot point for the suspension in roll and the reaction point for cornering forces.

To avoid being called “unsafe at any speed,” like the Corvair, it is imperative to lower the roll center height. The early Corvairs (along with many of our competitors) have a very high roll center. This can cause over steer stability problems during aggressive cornering. Additionally, high jacking forces cause the body (and CG) to lift while cornering, which is especially dangerous on a trike.

Motor Trike effectively lowered the suspension's roll center height, and designed our anti roll bar to work with the lowered roll center height.

Steering and stability are greatly improved when scrub is minimized. Scrub is synonymous with bump steer and is used to describe a vehicle's tendency to change track width as the suspension travels.

Minimizing scrub reduces the tendency to wander or skip sideways over rough roads. When scrub is minimized to only small amounts, tire wear is also reduced.

The last criteria for the suspension design was that of reducing install time and still maintaining the highest product quality. The frame, suspension, and drivetrain are completely assembled in-house, ensuring quality build and a streamlined install procedure.