There is no need for you to read all this. It gets kind of technical. If you are shopping then the #1 thing is to ride stuff and talk with an expert. But we offer this discussion of types of recumbents anyway. Knowing this might streamline a conversation with our staff if things get technical.
Among recumbent bicycles (2-wheelers) there are long wheelbase (LWB) and short wheelbase (SWB) designs. Long wheelbase has the front wheel ahead of the cranks (the assembly that the pedals are on), and SWB has the cranks as the foremost thing on the bike. Long wheelbase bikes with a smaller set of wheels are called compact long wheelbase (CLWB).
Among tricycles, there are delta trikes, which have one wheel in front and two in back, which mainly tend to be like LWB bikes, with the front wheel ahead of the cranks (alternatives exist, but they are rare). There are also tadpole trikes, with two wheels in front and one in back, which are like short wheelbase bikes, with the pedals at the very front.
Seat recline and crank height
Long wheelbase (LWB) bikes and delta trikes tend to sit more upright, and they tend to have the cranks lower than the seat. Many short wheelbase (SWB) bikes and tadpole trikes are designed to be ridden in a more reclined position, but not all of them. Upright sitting SWBs, like the Lightning Phantom, are more common than highly reclined LWBs. SWB bikes and tadpole trikes tend to have higher cranks, usually about level with the seat, and some even higher. Very high cranks reduce your aerodynamic profile (which is good), but they can cause poor blood circulation in the legs of some people, canceling out that benefit. Having both an upright seat and high cranks puts the rider in a more tucked position, giving better acceleration and climbing.
Long wheelbase bikes usually sit lower to the ground than short wheelbase bikes. Between both the more upright sitting position and the lower seat height, LWB models tend to be easier to stop and start than SWBs, making them more practical for stop and go city riding. The more upright seat of the LWB puts the driver’s eyes at about the same level as those of a person driving a car or a light truck, so it isn’t like your looking up under people’s bumpers on these bikes.
Delta trikes, on the other hand, tend to sit higher than tadpole trikes. Tadpole trikes sit quite low, giving them good aerodynamics and light weight. These features, along with the reclined sitting position, recommends tadpoles for “road bike” riding out on the open highway. For neighborhood riding, delta trikes tend to better due to their more elevated seat and tighter turning ability.
The very low seat of tadpole trikes makes it like a 3-wheeled version of a low racer, which a specialized form of SWB bike designed for time trials on a track. Reclined SWB bikes with a pair of large wheels are called high racers, and they aren’t as good for stop and go driving.
Over seat Steering
Now it gets more complicated.
Roughly speaking, there are two types of steering: over seat steering (OSS) and under seat (USS). With OSS, your heads are held in front of you, much like when you are driving a car. There is no weight on your hands. With USS, the handlebars connect beneath the seat. Sometimes your hands are actually beneath the seat, but sometimes the handlebars wrap up around the sides of the seat and your hands are just above your hips. This latter form of USS is sometimes called side stick steering, and is the way most tadpole trikes steer. We don’t really consider side stick to be truly under seat steering, but it is physically much more similar to USS than OSS.
Tiller OSS is typical on LWB bikes. The handlebar riser comes up from the headset (where the front wheel fork pivots to steer) and then it pulls back from the steering axis. How much “tiller” the design has is the measurement from the steering axis to the handlebars. Some people will tell you that “tiller is bad,” but what they really mean is that excessive tiller is bad. Having some tiller gives you easy control for tracking a straight line at speed. Too much tiller means excessive swinging of the bars left and right just to keep balance. In order to keep tiller to a manageable level, LWB bikes have a relaxed head tube angle, meaning that the steering axis is farther off of vertical than it is on an ordinary bicycle.
Riser OSS steering is typical on SWB bikes. The riser comes up from the front fork. We call the older style of riser steering the praying hamster position. (This from the same culture that gave us terms like aero-belly.) You pull the riser back to an adjustable stop so that the handlebar is quite close to the rider’s chest, lending to the name. By pulling the bars back you get some tiller for easier high speed tracking. By reclining the seat you can pull them back more and still keep some clearance from your chest. Some bikes have fixed risers that don’t pivot. This saves weight and can offer more pedaling torque.
Another style of riser steering is called open cockpit, or “tweener bars” or “the superman position.” The riser might pivot forward to help with getting on and off, and to adjust for arm length, but not always. In this position, the bars are farther away from the riser, often ahead of the steering axis. The knees come up behind the handlebar and the arms wrap around the knees to hold a wider bar. Tight turns are a little more difficult with tweener bars since the end of the bar can hit a knee when pedaling through a tight turn. This position is more aerodynamic and lets you keep your arms more extended.
Sometimes a LWB bike uses riser steering. The steering connects just ahead of the seat and a linkage connects it up to the fork in front. This design is called linkage steering. It allows for a more reclined position on a LWB, since reclining with tiller OSS results in too much tiller. Linkage OSS bikes usually have a more vertical head tube angle than tiller OSS bikes. Such designs have been called medium wheelbase (MWB) for that reason.
Under seat Steering
Under seat steering had faded from the bicycle market, but side stick steering is still very popular on tadpole trikes. USS can be divided into three types: thumbs up, thumbs in, and thumbs forward, describing the orientation of the hands when gripping the bars. USS works best on SWB or tadpole designs, since the steering apparatus is all close to the seat, which keeps the handlebar under the seat. It can be used on linkage steering LWB bikes and delta trikes as well.
Thumbs in USS is not very ergonomic, but it is easy and cheap to build. It keeps the hands far down, leading to lower weight and shorter cable runs. Thumbs forward is also a low style of USS. It is more ergonomic but requires a more complicated handlebar design. Thumbs up is the most ergonomic and it allows for a higher hand position, such as side stick steering. Some trikes have thumbs in side stick steering, such as TerraTrikes.
Side stick USS is particularly popular on tadpole trikes for the practical reason that to mount the trike the rider stands ahead of the seat, straddling the trike forward boom, and sit backwards into it. With riser OSS the handlebars get in the way of sitting down. We have seen riser OSS tadpole trikes, including a famous racing model.
Trike Under seat Steering
To steer the two front wheels of a tadpole trike you need a more complex assembly. We see two primary types. Indirect steering is the classic form, with a yoke-shaped handlebar pivoting under the seat and two steering rods reaching out to the front wheel hubmounts (variously called kingpins, kingposts, hubmounts or spindles… sheesh). Direct steering is a newer innovation. Here, the handlebars are two separate short pieces that attach directly to the hubmounts. A single linkage connects the kingpins. There is no central pivot under the seat. Direct steering is lighter and simpler than indirect, with much easier adjustment. Its main problem is that it transmits more vibration from the front wheels to the hands. Direct steering trikes are not for everyone, but it has its fans.
Happily, seat types are not so bound up with other factors like wheelbase, steering type and headtube angle. However, seats are proprietary and usually not interchangeable between different manufacturers’ ‘bents. We need the seat to be firmly connected to the frame, as it is a part of the drivetrain. Often the seat integrates into the frame, which limits adjustability but increases power and safety.
Seats come in two main types: shell and mesh. Shell seats are the oldest and simplest style, a rigid material like fiberglass or carbon fiber molded into a cup shape fitted to sit in. Then it is covered with a pad for comfort and to aid circulation. They are light and stiff, so well suited for racing. They can be surprisingly comfortable, but not for everyone. Shell seats are only found on expensive bikes that need to be ultra light, or else really inexpensive ones. They are only practical on reclined seats. Sitting too upright on a hard seat leads to a condition called recumbent butt, often solved by taking a short break while riding.
Mesh seats are much more common. These use a fabric mesh stretched over a metal frame, much like lawn furniture. Mesh seats come in two types: mesh back and full sling. On a mesh back seat, the rider sits on a foam cushion that rests on the frame of the bike and reclines against a mesh seat back. On a full sling seat, the rider sits on tensioned mesh.
Full sling is regarded as better for blood circulation, but the tricky thing about full sling seats are how the nose of the seat is supported. Some designs use a “saddle horn” at the nose of the seat that allows for a cut away, triangular shaped base, which helps with getting the feet down and for pedaling on lower cranks. But the saddle horn can conflict with some people’s anatomy, depending on how they are built. Other full sling seats use a square front, which avoids the saddle horn but makes it harder to decline the legs to a lower crankset.
A recent development of the full sling seat is Bacchetta’s Euro-mesh seat. This uses an ovular metal frame, resembling a shell seat in dimensions. They stretch a mesh over that, with a foam cushion from a shell seat on top of it. The narrow contours of a shell seat helps smaller people get their legs to the ground. It also gives the aerodynamic advantages of the narrow seat. It has more give and breathablilty, and only slightly more weight than a shell seat. We consider this seat to be a great innovation in SWB bikes. Many people have trouble comfortably starting and stopping on a high seat. The Euromesh seat needs to be reclined.
Seats move relative to the crankset to adjust for leg length. There are two ways of doing this. The usual method is for the seat to slide along the frame. In some cases, the seat moves between fixed mounting points on the frame. This type doesn’t give as much fine control over leg length, but reclining the seat will serve to increase leg length slightly. Overall, sliding seats are the most common kind os seat adjustment system.
The other method, which we see only on short wheelbase bikes or tadpole trikes, is called telescoping boom. This means that the boom, or the section of the frame sticking out ahead of the front wheel, slides fore or aft. This method has the advantage that the seat stays fixed to the frame with near-optimum weight distribution between the wheels. Re-sizing the frame is more hassle, since the chain must be re-sized each time the boom is adjusted. There are idler assemblies that can take up the slack of the extra chain, but they inevitably cause noise and lend extra weight. Some designs have used both sliding boom and sliding seat so as to let the rider optimize their sitting position relative to USS handlebars mounted on the frame.
Some designs have used a sliding crankset that clamps to the main frame of the bike. This design means that short riders have lots of extra bike sticking out ahead of them. There have been MWB bikes with linkage steering that have used telescoping booms. This design requires extra fittings to insure that the front wheel assembly doesn’t collapse from the boom rotating in the main frame, under the rider’s weight.
Add it all up
Different types of recumbents have different strengths and characteristics. You should discuss what kind of riding you want to do with experienced recumbent experts. And you should sit down and feel how the various frame types, seats, and steering arrangements work for you.