Although the suspension makes your ride smooth, the tires absorb most of the shocks caused by road hazards. They flex or move over irregularities on the road surface, reducing these noticeable shifts over road surfaces. Tires help to propel you forward by means of traction, gripping the road and allowing the driver to accelerate, brake, and steer.
Tires are constructed as either bias ply (layers of cord and rubber are criss-crossed) or radial ply (the plys are parallel and perpendicular to the tread) with steel belts/threads. Radial tires are constructed to last longer and they are more flexible than bias ply tires. The downside to radials is that a strong impact with a pothole or other obstacle can cause the steel belts to separate which leads to tire blowout. Routine operator maintenance on tires includes keeping proper inflation levels (usually 35 psi for radials and 32 psi for bias -check the manufacturers recommendations) and looking for uneven or unusual tread wear. Check the tire treads. Underinflating or overinflating tires can be dangerous and reduces the life of the tire.
Tires are rated according to the Uniform Tire Quality Grading System for traction, temperature, and treadwear. Traction and temperature are rated with an ABC scale with “A” being the best and “C” meeting minimum government standards. Tread wear is also rated, but on a numerical scale. The higher the rating, the longer tire tread is expected to last. A mechanic or tire salesman can translate the rating into approximate expected miles before you should purchase replacements.