from my experence it is what brand of car u have ... for instance an associated shocks gets dirty about 35 minutes sooner than a losi and a jammin shock last about 15 minutes longer than a associated but cleen your shocks an replace seals about every gallon and u are good to go
a good way to see how well your shocks are is flip your car over and press down on the wheels to preload the shocks if u feel a delay in the damping u prob have a seal problem or possably a bad bladder if u have oil on top of blader replace that if not replace seals
thats jus a good way to check your shock on race day to see if they need work
Jr-