There are a number of factors that can alter a vehicle's ride quality, and almost all of them can be upgraded relatively easily. Rotating and balancing the tires often grants the greatest instant improvement in the ride, and if the vehicle still pulls to one side afterwards, then it requires an alignment. Shocks and struts are another big factor in allowing the vehicle to glide down the road smoothly. If none of these improvements drastically increase the ride quality, then there is a chance that the vehicle's frame could be slightly bent from a previous collision.
The largest factor that affects ride quality is the tires and how they meet the road. On a new vehicle, the wheels should be perfectly aligned and each tire should glide across the pavement evenly. As drivers travel over rough terrain, the air pressure naturally drops and the wheels slightly favor one side over another. By rotating and balancing the tires, they are able to remain in good condition for much longer periods of time.
If the alignment is off by even a fraction on a vehicle, then it will pull towards the side of the roadway at moderate speeds. Not only does this make operating the vehicle more dangerous, but it also has a drastic effect on ride quality. The tires will also wear unevenly when an alignment is needed. As soon as a vehicle has the tires balanced to improve the ride, it should be taken for a complete alignment. It is also important to note that some vehicles require a four wheel alignment, and the quality of this service can vary greatly between mechanics.
Vehicles have shocks and struts to absorb the wear and tear of everyday driving conditions. Shocks are made of a piston inside a tube that's filled with hydraulic fluid. When the vehicle encounters a bump, the piston moves through the fluid, which provides resistance and slows it down, lessening the bump for the people in the vehicle. An amateur could be seriously injured trying to change the shocks by himself. An upgrade in this area can often provide enhanced stability and a higher ride quality.
In rare cases, all of the above upgrades will not have a significant effect on the ride. This usually indicates structural damage to the vehicle, and while the alignment can be adjusted to compensate for this problem, it will never be perfect. Many regions consider a wrecked vehicle a total loss after a serious collision for this reason alone, and consumers looking for excellent ride quality should avoid these types of cars. While they can be properly repaired every now and then, usually they are not.