Normally you'll start to notice damper wear approximately between 75,000-125,000 miles. The exact point when changes occur varies based on how you drive and the conditions of the roads you encounter. Damper wear happens gradually, therefore it can be difficult for a driver to sense it. It may be helpful to have someone else drive and evaluate your vehicle as another driver would have more of a "tabula rasa" perspective.
When the time comes to replace shock absorbers, you should get a damper that gives you proper control in the curves and smooth ride on bumps, tar strips and different road conditions. Proper handling, however, requires a higher rebound setting. A higher rebound setting means a firmer ride on bumps as the vehicle chassis will slam back down as its springs expand.
With older damper technology, most shock absorbers were designed to offer a good ride or good handling. What if you want both? KONI's FSD (Frequency Selective Damping) Damper Set provides lower rebound forces on higher-frequency piston movements (bumps) but higher rebound forces on lower-frequency movements (turns). KONI originally engineered FSD technology for the Lamborghini Murcielago and FIAT is using it on the new North American FIAT 500 Abarth. In our testing we found the KONI shocks with FSD technology provided our E46 test cars with an amazing balance between ride on our rough northern Indiana roads and proper handling on our autocross track. Although the FSD worked well for us as BMW shocks, they're also compatible with a variety of vehicles including, an Audi A3, MINI Coopers (both R53 and R56), the Mazda 3, Volvo S40, VW Jetta and VW Rabbit.
Thinking about lowering your vehicle when you replace dampers? Take a good look at KONI FSD Damper Set & Springs which combines FSD's with Eibach Pro-Kit Springs.
KONI FSD Damper Set
KONI FSD Damper Set & Springs
For more assistance in picking the proper damper set, take a look at "Choosing the Optimum Damper for Your Vehicle."