It is a significant risk factor for those with spinal disorders, increasing the amount of muscle fatigue and potentially damaging connecting nerves. Vibration is also believed to have significant impact on pain, the development of pressure sores, spasticity and general discomfort. It limits the time, distance and surfaces that users will consider for manual chair use.
Good Shocks and struts keep applied downward pressure to keep the tire in firm constant contact with the road at all times. They can: contribute to a smoother driving experience, help decrease drive and squat during hard braking situations, and reduce the force of forward gravity when braking under a panicked situation (helps avoid accidents!).

After building a PacMac track in its previous video in the Cat Trials series, Caterpillar set up a mock Hot Wheels race track featuring a variety of Cat equipment and life-sized versions of Hot Wheels cars.
A picture of the very incomplete gantry as it currently is, to give a better idea of what I'm up to: < > The only other way to get wheels to turn is either roll them freely unbound to anything, or attach them to a rotor. You can adjust the suspension settings to make them ridged, and you can use vertically oriented suspensions to prevent side wobble as if it was on rails. Wheels lack any form of propulsion on their own. They also lack any form of innate rotation ability. They're just cylindrical objects, exactly as they are in the real world (try welding a wheel directly to something sometime and see how well it spins). You need to provide an axle to them, and propulsion should you require it as well.