Once you are moving, the most important systems are steering and braking. Suspension is more than just comfort, it also is crucial to keeping your tires in firm contact with the road to keep the steering and braking effective. Shocks and struts are like the knees of the vehicle; they take the impacts so other (harder and/or more expensive to replace) parts don’t wear out quickly. Tires are the feet, which require the knees to guide them and keep them pressed to the ground, so the hips and torso don’t get heavily jarred and broken. New tires are expensive, proper alignment and suspension can help tires last longer. Most shocks and struts are good for around 50,000 miles.