Original Editor - Naomi O'Reilly as part of the Wheelchair Service Provision Content Development Project
No single model or size of wheelchair can meet the needs of all users, and the diversity among users creates a need for different types of wheelchair. Those selecting wheelchairs, in consultation with the user, need to understand the physical needs of the intended user and how they intend to use the wheelchair, as well as knowledge of the reasons for different wheelchair designs.
They can be in aluminium, steel (heavy but offer better grip), titanium (very light), or coated with plastic or rubber to assist with grip. In addition to the material, there are push rims with bars to facilitate grip by people with limited mobility in the hands.
Front Wheels (Castors)
It can go from 75 mm in diameter to 200 mm. The smaller the front wheels are, they will have less friction and are easier to turn, being suitable for interiors. For example, 75 mm and 125 mm they are recommended in wheelchairs for track sports, such as basketball. Large 200 mm wheels are more recommended for outdoor, and uneven floors, as it is easier overcome obstacles and do not get stuck in holes and irregular ground. The intermediate commitment for exterior and interior is the 150 mm wheel. Whenever we change the size of the front wheel, it is necessary to adjust the fork as it influences the level of the seat. The axis of rotation of the fork must always be at 90º with the ground.
They could be pneumatic or solid. The pneumatic tires cushion the imperfections of the ground but require maintenance (they can be punctured). The solid tires are harder to drive by do not flat and do not require maintenance.
The most common rear wheel is the 600mm diameter (24"). Smaller wheels (550mm / 22" or 500mm / 20") are used for child wheelchairs and for people with limitation of movement on the shoulders or for hemiplegic persons, so that they can reach the ground and propel themselves with their feet. The 650 mm (26") wheels are used for very high people and for practice of sports.
Solid tires offer less resistance to rolling, and do not require maintenance, but are more heavy and do not cushion the accidents of the terrain. They present worse grip on wet surfaces.
Solid inserts are an intermediate between solid and pneumatic. They do not require maintenance, have better grip than solid ones on wet surfaces, although they not cushion as much as pneumatics and weigh more than them.
Pneumatics are more comfortable driving because they cushion the accidents of the terrain and present a good grip on most surfaces. They are the lightest. As a disadvantage, they require more force to propel because they are softer (offer more contact with the ground, so offer more resistance to movement) and require maintenance as they can be punctured and need to inflate and monitor the air pressure to maintain its performance.
High Performance Tires
Tubular tires are very light and offer with minimum resistance to rolling. As disadvantage they are sensitive to punctures and require high maintenance. They are used for track sports wheelchairs such as basketball.
High pressure tires are used in sports and aluminium wheelchairs. They are very light tires, with high performance. They usually have an inner tube, it makes its repair more economical (only the inner tube should be changed).
Soft solids tires, with a weight similar to pneumatics, they have less rolling resistance and have greater durability than the solid insert tires and are also cheaper. A good compromise.
Plastic wheels hardly require maintenance, but they weigh more than spoke wheels. Aluminium spoke wheels are lighter and absorb better the rugosities of the terrain. The crossed radios offer a stronger frame and good suspension. For sports, usually straight spokes are preferred because they give greater rigidity, but the rims and axes must then be especially strong.
The most common locks are the push/pull to lock style. They are high mounted (it anchors the tube that is under the seat), and can be of two types, as activated by pushing forward or pulling backward.
For very light or sporty wheelchairs, scissor locks are often used. This type of locks can be placed lower (as they are anchored in the upper or lower tube of the frame). These locks are hidden under the seat, so they are more protected from impacts and do not bother transfers.
One-hand lock is for hemiplegic people who are only propelled with one hand, there is a type of brake that allows to lock the two wheels with one hand.
Lock extension is an accessory that is used to facilitate access to the brake of users with little mobility in the arms or hands, and thus facilitate locking. Although these types of locks are the most common, many variations exist that may meet user’s needs better than others.
Drum brakes are brakes that are not activated by the user but by the career. The career presses the levers (bicycle brakes type) located under the handles of the chair. This type of brake is the only one that serves to lock the wheels when the chair is stopped and as well to reduce the speed of the wheelchair, while in movement.
There are several types of armrests. They could be fixed, or removeable or foldable backwards. They could have different lengths of padding (normal or long). They could be adjustable in height. The padding is placed in various heights to adjust to the needs of the user. A desktop could be attached to the armrests with shape that allows to approach tables. Tubular armrests weigh less but have a lower support surface. For very active people, the armrests are usually removed and some side protectors to prevent wheels from dirtying clothes are proposed. 
Footrests can be fixed or removeable. To shorten the length of the wheelchair in tight spaces such as elevators, it is better that they are removeable. If there are no space problems it is more advisable that the footrests will be fixed as they are less fragile. The ideal position place the ankle in anatomical position 90º. However, in adults, the feet can interfere with the rotation of the front wheel rotation, so the angle tends to reduce. The most frequent angles are 90º, 70º and 60º.
Elevating leg support elevates the set of the leg, to adopt more comfortable postures. They are widely used in wheelchairs with reclining backrest. The footrest platforms are usually composite. They may be doubles or a single platform, with or without straps (for the heel or the forefoot). Usually the angle between the footrest and the platforms is 90º, but many platforms have the possibility of adjusting this angle to adapt to the specific needs of the users. 
All wheelchair users should be comfortable in their wheelchair, and a good cushion helps them to sit upright easily and comfortably. That is why every wheelchair user should have a cushion. A cushion is a very important part of every wheelchair. 
For many users, a cushion that provides some comfort will help them to use the wheelchair for a longer time. It is not necessary for every wheelchair user to have a pressure relief cushion, but users with limited or no skin sensation are always at risk of developing pressure sores when using a wheelchair without a proper cushion. These users must use a pressure relief cushion to help reduce this risk. An inadequate pressure-relief cushion is the one component of a wheelchair that is most likely to cause pressure sores, serious injury or premature death for those who are high risk for developing pressure areas.  Read More
Postural Support Devices
The needs of each wheelchair user will vary. All wheelchairs provide seating and postural support as well as mobility. Good postural support is important for everyone, especially for people who have an unstable spine or are likely to develop secondary deformities. The significance of good seating and postural support can mean the difference between the user being active and an independent member of society and the user being completely dependent and at risk of serious injury or even death.  Every appropriate, well-fitting wheelchair provides the user some postural support. The backrest, cushion, footrests and armrests all provide postural support when adjusted to suit the wheelchair user’s size.  Read More
- Gold Pictures. The Manual Wheelchair Comparision: Chair Accessories. Available from: https://youtu.be/64yXUfvRkKg [last accessed 6/6/2018]
- CarboLife. QUADRO - Setting New Limits. Available from: https://youtu.be/8f-aK0niPyc [last accessed 6/6/2018]
- William Armstrong, Johan Borg, Marc Krizack, Alida Lindsley, Kylie Mines, Jon Pearlman, Kim Reisinger, Sarah Sheldon. Guidelines on the Provision of Manual Wheelchairs in Less Resourced Settings. World Health Organization; Geneva: 2008.
- Sarah Frost, Kylie Mines, Jamie Noon, Elsje Scheffler, and Rebecca Jackson Stoeckle. Wheelchair Service Training Package - Reference Manual for Participants - Basic Level. World Health Organization, Geneva. 2012