Thanks go to Donny Petersen of Heavy Duty Cycles, Toronto, for this condensed article on trike rear ends. January 25, 2003.
The topics discussed here are the Lehman "No Lean" suspension for Gold Wings and Harleys, independent suspensions, anti-sway mechanisms, differential or "spider" gears, posi-traction differentials and front end shimmy.
No Lean Suspension.
Lehman, an American company that builds trike kits for Honda Gold Wings and some Harley Davidson models, have a proprietary "no lean" suspension, which means they developed it. So what does this mean? Well for example, the post-WW11 HD45 trike Servi-car can't lean, period, because there is no rear suspension as it is a rigid frame design. A spring-loaded seat post that takes up the jarring, unforgiving road bump impacts compensates for a lack of rear suspension. Rear fork (swingarm), design is the single biggest factor on how a trike will handle. This, of course, has a direct and important influence on ride quality. Rigidity also plays a major role in trike rear fork design where "flex" is the enemy. Swingarm flex would cause the trike to lean in the corner resulting in decreased stability and heavier steering. Ride quality is directly proportional to lack of flexing structural parts. The Lehman swingarm is a one-piece, reinforced unit that is designed to control and reduce torsional effects. Torsion is torque induced twisting or rotational movement that affects rigidity and interferes with the stable forward motion of the trike. The rear end has a differential and solid rear axles. Rigidity in the rear fork design ensures that all three wheels stay on the ground where they belong while cornering. Furthermore, the trike center of gravity stays where it belongs, centered over the rear end, rather than shifting along with the suspension during the cornering process.
Independent Trike Rear Suspensions.
Independent suspensions are just that. Each shock can act on its own depending on the forces applied. With this system one shock can compress while the other is allowed to extend. If we are turning right, the shock on the trike's left side will compress because the center of gravity and therefore weight is shifted in that direction… the trike wants to go in the same straight direction via momentum but is being forced to turn. On the right side, the shock is being forced to compensate for the weight transfer away from it. Therefore, it will extend. No Lean suspension is the opposite of this where both shocks are rigidly encouraged to maintain or approximate the same length in a turning situation. Independent suspensions will not allow a trike to corner as fast. The forces of weight transfer and a moving center of gravity will induce "body roll" or sway, which creates a less stable ride. The trike may feel like it will tip if too aggressive a turn is attempted and must be slowed down until the turn has been negotiated. The No Lean suspension is not as comfortable as an independent one. However this is a matter of degree.
Independent suspension is the best option for trikers who want comfort and who are not interested in riding dangerously.
Independent suspension trikes often employ anti-sway apparatus, which may be referred to as limiting kits. They limit the amount of opposing shock travel relative to each other. The bottom line is that the independent suspension loses some of its comfort or smooth ride benefits but makes travel around a corner more efficient. Anti-sway bars bring a true independent suspension towards but not achieving a true no-lean suspension. To me, safety is the ultimate goal before anything else like aesthetic changes; on two or three wheels, the better the handling the safer it is. For this reason I prefer No Lean first, anti-sway independent second, independent suspensions third with rigid in last place. If comfort is the primary goal then independent suspensions move up the list.
[NOTE! Fusion Trikes employ anti-sway independent suspension on their passenger trikes and live axles on their delivery trikes, unless a customer specifically requests a sports trike (for example) with a live axle].
Differential or "spider" gears are found inside the carrier in the differential assembly. The differential assembly is the unit the rear Harley belt pulley attaches to and drives. The assembly extends to both rear wheels transferring the horsepower and torque to them. The spider gears allow one wheel to turn fewer rotations while the other turns more rotations. This is needed for turning corners. In a cornering situation the inside wheel does not travel as far as the outside wheel therefore requiring less rotations. The differential carrier should be greased at each regular service interval. Give one pump of grease for every 1000 miles since the previous service.
A total posi-traction system drives both wheels according the same number of rotations each. This is for drag-strip racing but on the street the inner wheel would "squeal" during cornering because the inner wheel is turning the same number of rotations as the outer but it is not travelling as far. Some posi-traction systems have a slip component [limited slip diff] whereby if the drive wheel spins for whatever reason the drive component is transferred to the other wheel. This is great if one wheel is spinning on ice for example; the drive component is transferred to the other wheel, which hopefully can gain traction. This type of posi-traction allows for some slip of the inner wheel while cornering to eliminate the "squeal". This is another reason why some homemade trikes may be unsafe. If the differential on these have posi-traction the trike might spin out on corners or in adverse handling situations. Therefore it is evident that we do not want a posi-traction differential on a trike for the above noted reasons.
Drive Shaft Differentials.
Many of the Japanese and European bikes have drive shafts which require the use of universal joints for transferring the power back through the transmission output shaft to the axles connecting the two wheels. Universal joints are not needed with the Harley trikes but are very necessary on drive shaft models. A Universal joint allows for and takes care of changes in drive angle. The angle of drive must change because the transmission is stationary while the wheels go up and down with the suspension. Universal joints vibrate due to their design. This vibration is self-cancelling on cars through design because the joints are always in pairs. A motorcycle trike uses them singly. [NOTE! Fusion Trikes installs a Universal joint on each end of their bike trike's drive shafts]. There are needle bearings inside the universal caps. For this reason all universal joints are designed to have a minimum of a 1/2-degree of working angle. This is necessary to ensure that the bearing rollers roll. At no angle or those less than a 1/2-degree the needle rollers have a tendency to remain stationary which causes wear, vibration and then failure. The rear universal joint should be greased every 3000 miles or more often under severe driving conditions. There is no driveshaft on the Harley Trikes as the stock rear belt drive and pulleys very ably drive the Lehman designs.
Front End Shimmy.
Side to side movement in the trike rear end's 2 wheels is transferred forward. This is systemic to all trikes and is a result of the geometry of the machine. It results in front fork shimmy or shake. This can be annoying especially with aggravating road conditions. It is certainly tiring if touring. The shake is easily corrected by utilizing steering dampers. This is an adjustable hydraulic attachment that looks a little like a door closer. It attaches to the front fork tube near the top and the other end is similarly attached to the frame downtube. Some riders feel no need for a damper while others use only one. Others prefer a damper on either side. Another way that can be used independently of or in conjunction with damper(s) to control shimmy are raked triple trees. While not advisable on 2-wheelers, raked triple trees work very well on bikes with sidecars and trikes… in other words with 3 wheels.
The safety of trikes has improved immeasurably over the years. They are a viable alternative to two wheels for those that want to experience the pleasures and therapy of wind in your face that a car can never provide. We build trikes on a regular basis for enthusiasts and others, meaning older bikers that refuse to give up riding but can no longer hold up a heavyweight bike because of age, or whatever. We build custom clutch/shift/braking systems for the disabled. We have hand-operated proportional braking systems that activate all three brakes at the same time safely for those that cannot use their legs. These people refuse to give up, persevering to get what they want and above all enjoying the freedom that riding bestows. There is a proliferation of trike clubs across North America to suit every facet of the lifestyle. Fusion Trikes' mission is to make triking as popular and accepted as biking is in South Africa. The trike community is growing rapidly, but Fusion Trikes is the only company in South Africa designing and building our own range of awesome and versatile trikes for the motoring public. As our customer base grows, we will soon be hosting our own events and runs and above all creating an environment for companionship with your peers.