The Four Wheel Mobility Scooter
This article explores the four wheel mobility scooter, its advantages, and disadvantages.
The four wheel mobility scooter will be more expensive than a three wheel scooter due to the cost of manufacturing the steering system which will be far higher due to its greater complexity.
The three wheel scooter follows the same unsophisticated design principles behind bicycles, tricycles and motorbikes. This entails a basic fork around a wheel that is attached, via a bearing, to a frame and some form of steering control such as handlebars or a tiller.
This simple solution is easy to produce, and therefore offers low cost of manufacture, it does however suffer from inherent instability in all but the least challenging of environments and also necessitates cautious use by the driver.
The primary challenge the four wheel mobility scooter design faces was discovered early on with trains. When negotiating a bend, the outer wheels must travel further than the inner wheels. In trains this was solved by a combination of limiting the maximum curve, and lean angle or camber, of any corner and bevelling the wheels so that the outside wheels effectively get larger than the inside wheels, which also become smaller, when turning.
This solution, while ingenious, only works for a vehicle travelling on a track and the curves all need to all be extremely similar.
In a vehicle that will not have the advantage of tracks and precisely configured bend the two front wheels cannot turn in to a corner at the same angle. The outer and inner wheels must travel along different radii, and consequently at different speeds, thereby removing the need for the tyres to slide when negotiating a curve.
The principle that allows two wheel front steering to work efficiently was first put forward by Erasmus Darwin, however, due to the fact he did not patent he gets little or no credit for this.
It was left to Rudolph Ackermann to patent the design and henceforth it would be known as Ackermann Steering Geometry, and, though there are slightly different approaches in use, such as rack and pinion, they all rely on the same basic rules and geometry.
The inherent complexity of this system limits the turning curve drastically just by the space required to house its active components.
This design can also suffer from front end “stutter” at low speeds when making a tight turn. This can be felt as vibration, or judder, at the controls and can even lead to the scooters understeering on slippery surfaces.
The four wheel mobility scooter requires axles attached to a set of pivots and gears which transmit the desired direction being requested by the driver, these take up space exactly where your feet should be in order to offer you a comfortable and ergonomic seating position. The front wheel arches also dictate an absolute range of foot position with no provision for adjustment. Additionally, the turning circle of the vehicle is limited with this configuration.
So, let’s look at a few basic types of four wheel mobility scooter and how these characteristics affect each type.
Firstly, the heavy duty or off-road genre.
These feature oversize wheels in order to give them the required performance, and to look “sporty”, however there is a huge downside to these which is that they severely impact available foot space, consequently requiring the wheelbase to be lengthened.
The lengthening of the wheelbase further compounds the limited turning ability associated with four wheels, making the turning circle even wider.
This type of scooter also tends to have long travel suspension which makes the need for already large mudguards to be bigger all round. This again decreases legroom and, eventually means those with longer legs will need to place their feet on top of the wheel arches, which is as far from being ergonomically sound as it can get. The only person likely to benefit from prolonged use of a scooter in this position is an osteopath or chiropractor.
The actual need for this type of scooter is also questionable with most places you would wish to visit outdoors having perfectly usable and accessible footpaths.
The large size of these scooters means they are really only of any use out doors and they will be intractable in most indoor settings.
So, the next choice is a medium sized four wheel mobility scooter which will indeed offer a far more practical day to day solution to your mobility needs and feature greater stability than its three wheel equivalent.
However, this stability will have sacrificed agility. You are likely to find yourself making multipoint turns in tight spaces. This type of scooter will probably allow most people to adopt the two available seating positions on this configuration. The first with your feet in the footwell or the second resting on top of the wheel arches and, this means. with no possible adjustment, your body is forced to conform to the confines of the scooter as opposed to the scooter adapting to you.
Then we have compact four wheel travel and boot scooters.
These are small and short and as such suffer an from even greater compromise when it comes to your comfort.
They tend to feature smaller wheels in order to offer increased portability and to a lesser degree to grant greater legroom, the smaller wheel arches giving more room for your feet.
These small wheels limit the ability of the scooter to deal with anything other than quite small lumps and bumps, potholes can be a serious issue. This effectively means, any stability advantage you would have gained with the four wheel layout, has been negated.
The size of the wheels likewise limits motor size and, due to the nature of gearing, this reduces available power.
This lowered drive power severely can impact the scooter’s ability to tackle gradients and range can also be markedly decreased due to the simple fact a smaller wheel has to be rotated more times to cover the same distance as a larger wheel.
So, just how does the Quingo range overcome the issues surrounding these steering solutions?
Our Quintell™ Tri-Wheel system offers effectively two autonomous steering racks, of our own radical design, on each side of the scooter.
These act independently and actively in relation to the central front wheel. This system for articulating the wheels is unlike any that has preceded it and offers spectacular benefits over both of the other systems available.
Our system allows for articulation of the front wheels being comparable to that available to a three wheel scooter, and far exceeding that of any four wheel mobility scooter.
While the large central wheel of our system is responsible for the turning of the scooter the smaller out-rigger wheels give the scooter stability to rival any four wheel design and eliminate the tipping so common in three wheel configurations. It also offers an ability neither of the other designs can come close to, the ability to climb kerbs at up to a 45° angle in complete safety.
Our Tri-Wheel Steering gives you up to 80% more foot-space, when compared with a similar four wheel mobility scooter, and our Adaptive Floating Footplates are designed to conform to your body’s needs which simply means you will be more comfortable.
So, just based on the capability of our steering solution alone, the five wheel Quingo, we think you will concur, is the best available option.