Index Recumbent Trikes Rigid VS Suspension

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Rigid Frame and Suspension Frames

Just like in the bicycle world recumbent trikes started off with rigid frames (rigid meaning no suspension). Suspension adds cost,weight and complexity and in return provides a better ride and in some cases a vast improvement to handling.

In reality all trikes with pneumatic tires have suspension

Appropriately enough pneumatic tires were originally invented in 1887 by John Dunlop for his son's tricycle to give a smoother ride. Today we see "balloon tires" often used to soften the harshness of rough pavement. Tires have limited effectiveness in damping out the bumps; fatter tires do a better job of damping but with the penalty of added weight. Beyond about 2.00" width the improvements to damping are "outweighed" by the added weight.

Rigid frames have the advantage of simplicity, cost and weight. Most of the time Mesh seats are favored on rigid frame trikes as the Mesh gives a bit over bumps and reduces the harshness. Some have tried mounting the seat on springs only to find the seat squirm with every pedal stroke. A Mesh seat also squirms a little bit but its often imperceptible. Some rigid frames actually have some flex built into the frame design, more commonly with steel, but some aluminum frames are also designed to provide some flex. Both Catrike and ICE frames share this quality although the flex is pretty minimal.

Rear Suspension

To date none of the Delta Trikes have suspension where it would be most effective, on the rear wheels. There are few that have a rudimentary form of suspension on the front so we'll focus the discussion on tadpoles.

Human beings sense motion within the inner ear and with the head being at the highest point and closer to the rear wheels we feel the rear wheel jounces with much more sensitivity then front wheel jounces. Also as the rider is in the middle between the front wheels, only half of the jounce would move the rider if only one wheel is jounced.

That's part of why some trikes offer rear only suspension, but none are offered as front only suspension.

Rear suspension uses a Swingarm with a single hinge point. There are some newer grades of Mountain Bikes that offer a more complex system of multi-point hinge actions but the complexity is really only beneficial when using rear wheel braking. Multi-point is not likely to be included on a mainstream trike at any near point in the future.

As the chain is pulling the rear wheel forward the tension forces on the wheel sprocket could be partially converted to force the frame to squat. As pedaling forces change with the positions of the feet an effect known as "Pogo" takes place. Pogo effects can be minimized and even eliminated given a proper design. The key is to position the pivot point for the Swingarm on exactly the same plane as the chain runs through. That's easier said then done, and none of the OEM's have succeeded in building the perfect Pogo - Free rear suspension.

The animation below gives a visual perspective on the causes and effects of Pogo:

   

The effects of Pogo sound worse then they really are. In terms of efficiency and power loss its really quite minimal in most cases with most modern trikes the efficiency losses are under 1% most of the time.

Extreme conditions can lead to excessive Pogo:

  • Heavy loads that force excessive droop resulting in large Offset Angles (See animation)
  • Insufficient spring force for the rider/load on the swingarm
  • Poor chainline geometry

Keep in mind that while pedaling the chain tension will go from about 30% to 100% twice every revolution. If the rider was capable of maintaining 100% chain tension through every crank revolution, the Pogo effect would only occur once when they started pedaling, and once when they stopped. In the real world the forces are induced twice with every crank revolution, so the frequency of the jounce is 2 * Crank RPM.

Shocks aka Dampers reduce the effects of Pogo. Most folks think shocks simply absorb (dampen) the motion energy, but they do much more then that. Shocks also control both the speed of the motion, where springs control the distance of the motion. Shocks will reduce Pogo losses where springs will reduce the distance traveled, but not the loss. Rear suspension will generally be more efficient with some level of shock absorption.

Elastomers are have some damping capability built in and can be an effective spring-damper system when properly matched to the suspension. They aren't quite as effective as a shock-spring is but they are lower cost and lower weight while providing adequate control with a properly designed swingarm.

Cargo Racks may be mounted on the frame (Sprung) or on the Swingarm (Unsprung).

Sprung Racks are generally an OEM offering and not all OEM's offer them. Sprung Cargo will affect the frame droop and for those carrying a heavy load longer distances it is recommended that the spring pre-load be adjusted to maintain proper ride height. If using an Elastomer spring it may require changing to higher rated elastomer.

Unsprung Racks are usually an owner added item usually relying on aftermarket racks with homebrew engineering to attach them. Lacking the inertia of the rider and trike frame weight Unsprung Racks live a much more violent life of shaking about the bumps. You may not want to carry anything breakable in an Unsprung Rack attached to a Swingarm.

Swingarms themselves typically only add about 4-12 ounces of weight over a Rigid Frame. Elastomers may add about 6-8 ounces, Spring Shocks add about 16-20 ounces, airshocks add about 12-16 ounces. Typically the added manufacturing cost of a swingarm will range from about $50 to $150. Elastomer manufacturing costs are under $10, and Spring Shock costs in volume start at about $20. Airshocks start at about $100. Like any option, OEM's will make pretty good margins on suspension components.

Typically swingarms are designed with 3-4" of travel. The more travel they have the higher the frame tube has to be to avoid hitting the pavement at full droop. Normally the ride height with rider and any cargo weight is set to about 25-30% droop; generally just under 1" lower then with no rider/cargo. Spring pre-loads can be adjusted to a point but a general rule of thumb is no more then 2 turns on the adjustment collar. If you need more then that, the spring is too soft.

Rigid Frames offer the least weight, lowest cost, and most efficiency on smoother surfaces. Where a "racing" trike may be fitted with a hardshell seat and high pressure racing tires the rider is giving up comfort for speed. Mesh seats offer a great increase to comfort on a racing trike at the expense of losses to the motion of the seat fabric. One of the really great early models of racing trikes was the ICE Micro that had a very lightweight rear suspension and a hardshell seat. The weight savings from the hardshell were greater then the added weight of the suspension.

Catrike produces one of the most popular mid-range Rigid Frame models, the Expedition. Equipped with a 26" rear wheel the ride is smoother then a 20" rear wheel as the larger diameter tire spreads the bumps out over a longer path and softens the blow of a bump. Equipped with a Mesh Seat adds a bit more cushion effect. Riders may opt for a higher pressure road tire for higher speeds with a rougher ride, or a wider lower pressure balloon tire for a softer ride but slower ride.

Rigid Frames will never reach the ride quality of a Suspended Frame. That's not to say a Suspended Frame is better for everyone, but those who aren't chasing down roadies or riding in a more competitive style will appreciate suspension enough to justify the cost.

Front Suspension helps with the ride quality; while its a bit subjective, Front Suspension adds about 1/3 the comfort that Rear Suspension adds. The reason is mostly due to the distance ratio of the front/rear wheels to the rider's head, and in part because most bumps will only impact one wheel at a time. Where Front Suspension really shines is avoiding the need to slow way down over potholes of things like railroad tracks.

For the vast majority of riders Front Suspension only needs to soften the heavy jolts and generally about 2" of travel is all that's needed. Hard core off road riding is about the only time a rider will need more then 2" of travel. Very few of the Front Suspension model trikes offer shocks on the front suspension as few riders would benefit from them. The added weight cost and complexity will only benefit a few riders. Moreover, as the spring/shocks tend to be mounted directly in the path of the frontal air, they add to the aerodynamic drag at higher speeds.

As the front wheels provide stability suspension motion also allows the trike to roll or lean to the outside through turns. Likewise under braking the weight transfer to the front will cause the front to dive. Some of this motion may be undesirable which is why some trikes are just fine with rear suspension only. It is possible to offset some of the roll angle or brake dive through the suspension geometry and anti-rollbars.

Lever Action suspension is offered by ICE.

The forward leading angled levers provide anti-dive under braking.

As the wheel rises and droops there is no camber change. Camber change can give the rider the visual impression the wheels are unstable while moving vertically over rough pavement. Some small levels of camber change can be a good thing through turns although the zero camber change feature is better as the trike is pointed straight ahead.

Another advantage of this design is there is very little toe change as the wheel rises & lowers. Tow change causes a condition known as bumpsteer where a vehicle will move to the left or right as a result of going over bumps.

ICE uses a set of shaped elastomers as the spring/damper and are available in various hardness rates.

ICE is the only OEM to date that sells a system that can update their non-suspended models to suspended. It will raise the ride height by about 2"

 

McPherson Strut suspension is offered by HP Velotechnik on the Scorpion FS 20 & 26" models.

The upper side beam is fixed with an A-Arm locating the lower side of the front spindle.

HPV uses both springs and elastomers to control motion with external adjustability. There are multiple springs offered to properly tune the ride suppleness to the weight of the rider.

Unique to HPV suspension is an anti-rollbar that comes in three stiffnesses for enhanced tuning.

The geometry of this system has been carefully designed to eliminate bumpsteer.

Some brake dive is present. A little brake dive is actually an improvement as it gives the rider a little more margin of reserve from locking the brakes on a panic stop.

There is about 1° of camber change which gives the best compromise roll angle and bump effected camber change.

Pedaling Pogo is minimal can be nearly eliminated with the external pre-load stiffness calibration.

In 2013 HPV made some design changes to the geometry that provided several improvements over the prior years of FS models.

HPV also offers an off-road version of the Scorpion FS 26.

 

Dual Wishbone suspensions are favored when more then 2" of travel is required as the upper and lower control arm geometries allow a wider range of desired motion control.

They also offer a relatively easy way to adjust ride height and spring stiffness without replacing springs. On this model the ride heights have 3 levels each with an increasing stiffness as they lower.

While the ideal geometry can be perfected it takes a significant level of engineering expertise along with plenty of trial & error to actually perfect the design. Its also a packaging nightmare to balance the geometry requirements, chainline right-of-way, and rider leg clearance.

Spring/shocks and mounting plates will be an aerodynamic obstacle without the use of complex pullrods & bellcranks.

Steintrike has released two different dual wishbone systems among their model lines. The most recent was debuted on the Wild One and features the smoothest riding front suspension in the industry.

Several low volume and prototype trikes have been built with Dual Wishbones but only the Steintrike is readily available.

 

Most first time trike buyers will end up with a rigid frame as their first trike. After all, you wouldn't want to spend too much additional cash on a toy you may not end up using all that much. Its probably 1 out of 10 trike buyers who end up letting them sit in the garage as dust collectors. And probably 3 out of 10 will upgrade within another 2 years of buying their first trike.

The majority of suspended trike sales are upgrades for the buyers. Suspension is pretty much a personal preference. Its all fun stuff.