This week: Ergo

When hurdling along at 30 mph, bouncing off of rocks and logs and whatever else the trail throws at you, driver comfort must be taken into account during design.  There are many things about a car that effect driver comfort.  These include several aspects of the steering wheel, pedals, and shock settings.

As far as steering is concerned, wheel position, steering force, and steering range are all important.  The wheel position and angle are mostly personal preference, so we just check the placement with numerous experienced drivers before finalizing it.  Steering forces and the range of steering angle have more significant implications while driving.   Steering force is the amount of strength it takes to force the wheel to turn.  Modern automobiles have power steering to keep steering force low.  For our smaller vehicle, we don’t have to go to this extreme; in fact we have to make sure that there is sufficient steering force for the wheel to give some feedback to the driver.  The range of steering is important, since hand over hand steering, shown in the image below, is not preferred for off-road driving.  When you are being bounced all over the place, the last thing you want is to take your hands off the wheel.  Additionally, this type of car uses its full range of steering much more often than a road vehicle, as it must make tight corners and rapid steering movements.

Source: http://www.nzta.govt.nz/resources/roadcode/gfx/steering-hand-over.gif

Shock settings can greatly affect the comfort of the driver, but potentially at the loss of performance.  The opposite can also be true, for instance, we discovered that very stiff shocks in the rear were good for maneuverability as it made it much easier to slide the rear around tight corners.  The stiff shocks, however, made for a very rough ride on longer drives.  As a result, we had to compromise between performance and comfort for the endurance race.

The positioning of the pedals, as well as the distance they must be pushed, both play important roles in the feel of the car.  Touchy gas or brake pedals can make a car jerky to drive, so the throw distance of the pedals should be designed accordingly.  Additionally, the pedals should be positioned in a way that the driver’s feet and legs are comfortable when the pedals are not being used.  Following this logic, the driver’s leg should be comfortable while not putting any pressure on the brake pedal, as that is the most common position for that leg.