At Motor Trike, it took the perfect independent rear suspension to create superior rideability. Below are more in-depth tech facts about Motor Trike's patented IRS, including facts about our patented air ride suspension. Here, our engineers present what it took to deliver the best suspension ever offered. Motor Trike's IRS was created correctly from the start, cutting any “quick fixes” that would cost riders extra time and money, and meeting the 5 Things to Look for When Buying a Trike.
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Independent Rear Suspension
How Motor Trike Created Superior Rideability
1. Creating Superior Rideability
Not all independent rear suspensions (IRS) are created equally.
For example, a BMW and a Hyundai do not have the same performance characteristics. A Cadillac and a Corvette do not have the same ride quality.
At Motor Trike, we understand what makes a suspension good or bad, across all riding situations. Our IRS was developed to provide what our customers want and need based on our experience building trikes since 1994.
2. IRS Selection
The ideal suspension has always been the focal point of all of Motor Trike's conversions. Therefore, selection of the most ideal IRS was crucial.
Competitors have the following IRS options:
|IRS Design Options
|Trailing Arm||Inexpensive, simple||High roll center, no camber control|
|Semi Trailing Arm||Still inexpensive, simple, some camber control||Unwanted toe change can occur with camber gain, high roll center|
|Short Long Arm||Precise camber control, roll center height control||Expensive to produce, difficult to package around exhaust|
3. IRS Selection
Motor Trike selected a Short Long Arm Suspension with H-Arm and Camber Link
|Middle of the road cost option provides a reasonably priced kit||Cannot use for a steering application|
|Package around exhaust and still achieve good design parameters||Must maintain ride height due to camber change (air springs)|
|Ability to design for:|
- Low roll center height
- No toe change in bump or roll
- Precise camber control
- Small amounts of scrub
- Small jacking forces
4. IRS Design Criteria
Four major design criteria led Motor Trike's engineering team to create its current suspension:
- Traction/Grip—increase camber gain and lower CG height
- Ride Quality—optimize natural frequency and reduce NVH
- Leaning/Sway Control—correct roll stiffness and balance anti roll bar with roll center height
- Bump Steer/Stability—tire scrub, roll center height, and toe change
- 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.
7. Ride Quality
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.
8. Ride Quality
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.
9. Ride Quality
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.
10. Sway Control
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.
11. Bump Steer/Stability
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.
12. Bump Steer/Stability
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.
13. Install Time
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.
14. Creating Superior Rideability
Motor Trike's independent rear suspension was engineered to account for inconsistencies on the road and all kinds of riding situations. It was designed to complete a quality product that would lead to quality experiences for years to come. It was also created to satisfy budget-conscious consumers, eliminating the need to purchase rake kits or steering supplements, as the IRS accounts for varied riding conditions.