Everything from the suspension to the tires affects each other. The shocks are meant to absorb bumps in the road and control the movement of the springs that support the suspension. When they start to wear down, they can no longer do this effectively. The vibration that was previously damped by the shocks starts to permeate the vehicle and can cause damage to cargo, lights, refrigeration systems, and onboard electronics.
This extra vibration is also transferred straight through the tires, which can then start to bounce and shake across the road as they roll. This causes unusual scuffing and wear patterns called "cupping." Cupped tires cannot keep consistent traction with the road and can be unsafe to drive with.
Once cupping is noticed, tires should be replaced. Replacing shocks without replacing the tires will only slow the damage, not stop it. Once the tires are replaced the shocks should be replaced as well. Pairing new tires with old shocks will only ensure tire damage begins right away and will shorten the life of the tire. To ensure the longest possible tire lifetime and top driving performance, change your shocks when you change your tires.
Information provided by: Gabriel Ride Control Products
