If the shock is fully extended, then yes it will be representative. That's why you need to measure the shock first. If the shock is not fully extended then no.... you'll have to get a bit more involved in the test. You can do this by raising the rear of the vehicle and supporting it with jack stands under the frame so that the rear axle is hanging (it helps to take the rear tires off from this). Then put the jack under one side of the axle and raise it until its fully compressed. (FYI this method is an "easy" way to install 2" lifts without spring compressors ).