I don't know the answer to your question. I installed a set of blue and yellow Bilsteins on my '01 Ram dually at about 65,000 miles, probably in 2002, because the OEM shocks were worn out. I sold the truck at 325k miles and occasionally still drive it including a few months ago. Still has the same Bilsteins on it that I installed years ago and they still work, If their dampening has deteriorated I don't notice it. For normal highway use including heavy towing they are unbeatable and seem to never wear out.