Independence through Mobility - Chapter 4

Designing Each Chair to Fit

It is important that the wheelchair fit the needs of the rider. A customer's height, width, and level of disability will affect the design of the chair. How the customer intends to use the wheelchair will also affect the design. A customer who plans to race her chair will want a different chair from one who plans to ride his chair over rough and hilly terrain. Before beginning to make a chair, you will need to decide how large to make the seat, how long to make the footrests, and what size of wheels and handrims will best serve the needs of a particular wheelchair rider. While we encourage you to make chairs that truly fit the customer, we do not mean to imply that you must make each chair one at a time. It is much better to make chair components in batches and assemble the appropriate sizes to order. The primary purpose of this chapter is to outline the various customizing decisions that will go into each chair, whether you mass produce components, or make each chair individually.

FRAME HEIGHT AND LENGTH The standard wheelchair is designed for all purpose use by a paraplegic who is 5'4" (1.63 m) tall; 24" (61 cm) is a standard height for the back of the frame; 17-1/2" (44.5 cm) is a standard frame length. The height of the back of the wheelchair should be changed to accommodate the needs of different riders. As a general rule, the back should be as low as the rider's disability allows without being so low that it is difficult to pull the chair upstairs. Because of this, we recommend that the frame height not be any shorter than 22" (56 cm). Someone with a lower level of disability who has no difficulty balancing his or her upper body does not need as high a seat back as someone with quadraplegia. A well designed jig will accommodate different back heights easily.

The frame length is more difficult to change. The frame cannot be any shorter without changing the design to include smaller front wheels. The frame can be lengthened for people who want to race their chairs or for very tall people who feel they need the extra stability. The disadvantage of a longer frame is that it is more difficult to maneuver indoors. In addition, our sideframe brazing jig would have to be lengthened in order to make a longer frame.

SEAT HEIGHT AND WIDTH

The height and width of the seat can also be built to fit each individual rider. The seat should be high enough and the footrests low enough so that the rider's thighs press against the seat cushion. This will distribute the body weight, taking some weight off the buttocks and reducing the chances of getting pressure sores. The seat should also be low enough that the rider's feet are not left dangling. To find the appropriate seat height, measure from the back of the client's knee to the bottom of his heel. Add two inches (5 cm) to that measurement in order to allow enough room for the footrests to clear the ground. The resulting measurement is the seat height. It measures the distance from the ground to the front edge of the seat.

As a general rule, the following table will give you an idea of the seat height that is appropriate for people of different heights. If you are making a chair for an adult who is less than five feet tall (1.52 m), don't make the seat height any lower than 17- 1/2" (44.5 cm); just shorten the footrest to reach his feet. Wheelchairs with a seat height greater than 20" (51 cm) can be a bit top heavy and unsteady. It is also difficult to make a folding chair with a very high seat because the seat hooks will hit the fender when the chair is folded. Most riders who are more than 5'11" (1.80 m) tall prefer a seat no higher than 20" (51 cm) high. They add extra thickness to the front of their cushion to get additional seat height and thigh support without raising their whole body.

The narrower the wheelchair, the more places the rider can go; consequently, the wheelchair should be made as narrow as possible while still leaving enough room for comfort. To find the appropriate seat width, have your customer sit in a wheelchair that is larger than she is. Slide books in on either side of her until the books just touch but aren't squeezing her hips. A seat this wide will give most riders enough room to move while still keeping the chair reasonably narrow. Measure the distance between the two books and use this measurement for the width of the seat and seat back upholstery.

SEAT ANGLE

In our wheelchair design the seat and back recline 12~. An occasional customer will want a chair that is reclined less. Quadraplegics, and others who have trouble sitting up straight, may want the seat to recline further. Changing the angle of the seat will require making the wheelchair by hand or using a modified sideframe jig.

X-BRACE LENGTH

The length of the x-brace is determined by the height and width of the seat. The following table can be used to calculate the length of the x-brace. The measurements listed for the x-brace give the length of the tubing before it is filed to fit around the pivoting tube and seat support tube. (See Chapter 8).

SEAT HEIGHT AND WIDTH DETERMINE X-BRACE LENGTH

* These seat heights (measured at the front of the seat tubes) are too low for chairs with 26" wheels; the seat hooks may hit the axle sockets. Minimum seat heights: for 24" wheels is 17"; for 26" wheels is 18". For children use a smaller rear wheel.

** The longer x-brace lengths may cause the seat hook to bump against the top of the fender bar as the chair is folded, preventing the chair from folding all the way. This problem can be solved by using a longer fender that is welded to the frame at a point higher than the standard fender.

LENGTH OF UPPER FOOTREST TUBE The standard length for an upper footrest tube is 5-1/2" (14 cm). Since we have designed the footrest to be adjustable, most people should be able to adjust the standard size to fit. If someone needs a longer footrest, try using the 7-1/2" (19 cm) upper footrest tube. The best way to know whether the customer will need the longer size is to have him sit in an already completed wheelchair and see if his knees are raised too high.   LENGTH OF LOWER FOOTREST TUBE To fit a chair with a seat that is 16" (40.6 cm) wide, the lower footrest tubes should be bent out of two 21" (53.3 cm) lengths of tubing. For seats wider than 16" (40.6 cm), add 1/2" (1.3 cm) to the length of each piece of tubing.

HANDRIM DIAMETER

A larger handrim can give more pushing force to the wheel; a smaller handrim can push the wheelchair faster on level ground. The diameter of our standard sized handrim is about 6" (15.2 cm) smaller than the diameter of the wheel. Athletes who will be racing on level ground will probably want a handrim of a smaller diameter. A customer with limited arm strength who lives in a hilly area may want a handrim nearly equal in diameter to the wheel. Making a larger or smaller handrim will require making an appropriate sized die for the wooden bender (see Appendix A).

CHOOSING THE REAR WHEEL SIZE

Our wheelchair design uses bicycle rims and tires instead of the solid rubber tires used on conventional wheelchairs. Not only are bicycle tires more readily available, but they give a much smoother ride and are easier to push.

Choose the wheel size (the diameter and width) based on the kind of use the chair is likely to get and on the sizes that are available. The most common wheel size for general use, especially for in town riding, is the 24" by 1-3/8" pneumatic bicycle wheel and tire. A 26" by 1-3/8" wheel can also be used if the 24" wheel is not available or is too expensive. For small children a 16" or 20" wheel is often better, because it lowers the rider to the eye level of other children.

For country or farm use, a wider wheel is better. It will give the wheelchair rider more traction; this means less time stuck in the mud! A 26" by 1.75" or a 26" by 2.125" wheel is a very good size for country use. A 24" wheel is also fine, but it is unusual to find one with the wider widths. Combining a rim that is 1.75" wide with a tire that is 2.125" wide will weigh less and work well.

CUSTOMIZING THE WHEELCHAIR

Whether your shop mass produces components in different sizes and assembles chairs to order or makes each chair individually, you will need some kind of system to keep track of the measurements needed on each individual customer's chair.

We recommend keeping a file card or sheet on the customer that includes the following information:

CUSTOMER INFORMATION SHEET