Most people think about the backrest when they think about driving comfort. Lumbar support, seat back angle and seat shape all matter. But don’t forget the bit you sit on.

A vehicle seat wedge raises the back of the seat slightly. That small change can make a noticeable difference for some drivers, especially if the original seat position is not quite right for them.

1. Sitting too low in the vehicle – shorter drivers

Shorter drivers may sit too low in the seat. This can make it harder to see over the bonnet and feel properly positioned in the vehicle.

Raising the back of the seat will lift the pelvis and improve their view of the road.

For shorter drivers a seat wedge may also be more appropriate than a full seat cushion because a seat cushion will also raise the front of the seat and this may make the pedals too far away. 

2. Old or sagging vehicle seats

Over time, the seat’s foam and springs can lose some of their bounce. The rear of the seat takes a lot of load, especially under the driver’s pelvis. As the rear of the seat sinks, the driver may end up sitting lower than the seat originally intended.

This can change the whole sitting position.

The front of the seat fabric is usually anchored at the seat’s frame and hence remains at the original height, when the back of the seat base loses support, the hips sit lower than they should, and the seat starts pulling the driver into a slumped position.

A vehicle seat wedge can help restore the original seating position by lifting the rear of the seat base and adding fresher cushioning where the old seat has lost support.

3. Buttock, hip, thigh and leg discomfort

When you are in a car, your pelvis, buttocks and thighs can remain under fairly constant pressure for long periods of time. Unlike sitting at a desk, you cannot easily shift around, stand up, or change position very often.

This lack of movement can make pressure build up under the sitting bones, buttocks and backs of the thighs. For some people, this can contribute to back ache, hip discomfort or buttock pain.

Adding a wedge may help by slightly changing how pressure is distributed through the seat. It can also add a layer of newer, more responsive cushioning between the driver and the old seat base.

4. Hip angle and low-back posture

The angle of the seat base affects the position of the pelvis.

If the back of the seat base is very low, the hips may sit lower than the knees. This will close the hip angle and encourage the pelvis to roll backwards. When the pelvis rolls backwards, the lower back follows by flattening, slumping and increasing the strain through the lumbar spine.

Raising the rear of the seat slightly can open the hip angle and help the pelvis sit in a better position. 

5. When the built-in seat adjustment is not enough

Before adding any cushion or wedge, it is sensible to check the in-built seat adjustments first:

• raise or lower the seat if the vehicle allows it;
• adjust the seat base tilt, if available;
• change the backrest angle;
• check whether the built-in lumbar support is helping or making things worse.

Sometimes these adjustments don’t go far enough, or the seat simply does not suit the driver.

That is where a vehicle seat wedge may be useful.

6. Three different problems, one possible solution

A vehicle seat wedge may help with three different problems:

• Height / visibility — the driver sits too low and wants a better view of the road.
• Comfort / pressure — the seat feels hard, sagged, or uncomfortable under the buttocks, hips or thighs.
• Posture / hip angle — the pelvis rolls backwards, encouraging slumping and possible low-back irritation.

These problems often overlap, but they are not quite the same.

7. A few things to check that you get right

A wedge must improve your driving position, not compromise it.

After adding any cushion or wedge, check that:

• your feet still reach the pedals comfortably;
• your head is not too close to the roof;
• the lap belt still sits low across the pelvis, not up over the abdomen;
• the shoulder belt still runs comfortably across the chest and shoulder;
• The wedge should not lift the back of the seat so much that the seat base slopes forward. That can make you feel as though you are sliding towards the pedals, which is not what you want.

Final thought

A vehicle seat wedge is a simple idea: raise the rear of the seat base and change the way the pelvis sits.

The key is that the wedge needs to solve the problem you have. In the next article, we will look at what makes a good vehicle seat wedge, and what to avoid when choosing one.

About the author: Martin Rooke is a registered osteopath in New Zealand and inventor of Morfit. His writing focuses on practical solutions to musculoskeletal health that affect comfort and pain.