When should dampers be serviced or replaced?

OK let's be honest unless you have a competition car, you've probably never had your dampers serviced? Some of you will be running around in a 20 year old car with 100,000+ miles on the original dampers as well..

I noticed that KW were recommending the following intervals for their competition dampers:

Endurance Race, Circuit, Trackday, Drift: Maximum 6000km (3722 miles)
Tarmac Rally: Maximum 3000km (1861 miles) 
Gravel Rally: Maximum 1000km (620 miles)

I suspect there are many club motor sport competitors who don't get their dampers serviced until they have a problem with them. At the top end of tin top Motor Sport  - British Touring Cars - I gleaned from Penske that some teams will rebuild and often revalve after every meeting. 

Where does that leave dampers in road cars that are used for the odd event like a Track day or Sprint? 

The frequency of servicing dampers, depends on various factors, including the vehicle's make and model, driving conditions, and manufacturer recommendations. In general, there is no fixed interval for shock absorber maintenance, and it often depends on visual inspection and assessment of performance.

As a rule of thumb I'd recommend having the shock absorbers inspected every 50,000 miles and replaced if necessary. Of course if you start taking kerbs on track or hitting a lot of pot holes on the road this could be reduced greatly. Hence why the service regime KW specify for Rally use is so frequent. 

The best thing is to tune into the car and the way the dampers work, being attentive to changes in your vehicle's handling and ride quality to help you determine when servicing or replacing the dampers is necessary.

One of the significant upsides (or downsides?) of Bilstein monotubes is when they go, you tend to know about it as there is a significant loss of damping. The cost to rebuild a Bilstein unit also significantly less than some of the competitive products on the market. On the flipside the BC racing units often available as a full new replacement for less than the BILSTEIN rebuild..