With a real car such as a track car, you may have several spring options available to you. If you are a person who uses Tokico Illumina shocks or Koni's and then decide to use an Eibach spring, you aren't going to have a high degree of tunability. You hope they matched spring rates to each other well and usually they do. It doesn't mean you have the ride frequency that will give you the best performance for every application though. A street car requires a higher ride height and a lower suspension frequency than a dedicated track car. Tokico and Koni shocks add a nice degree of flexibility for a street car and the casual driver who occasionally wants to go out on a track but you can't adjust shock and rebound independently of each other. I take that back, Koni does make a true race shock that is double adjustable but you won't use it on your street car. On a single adjustable shock such as the ones I listed, when you adjust shock, it adjusts the rebound as well. On better, dedicated track coil over type of setups you can adjust both though and can get it to compress at a different rate than it rebounds. Since you don't go into those shocks and change your shock oils you change the shock and rebound settings for your track. In the r/c world, we can change shock oils although we can also go in and change the pack through different pistons. RC cars are the most tunable performance vehicles in the world and due to their small size should seem obvious that there are some techniques that are possible that aren't on a full sized vehicle.

You can feel if the front and rear of a real car are going up and down at the same time. You don't need to drop the car. You don't even need to go off roading. Just pick a street. You can tell the cars that have worn out old suspensions. Just watch the way they bounce over a hump or a dip in the road. A big old Cadillac pops in my head when I think of this. You are watching it bounce at it's ride frequency. This thread deals with r/c cars that weigh a few pounds that fit in your hand. It's obvious that you can pick it up. If you drive an rc car with no shock oil, you can also observe the rates at which each end bounces. It is far easier due to it's size to just do it on a bench. You fine tune it by running it. Onroad rc cars with very high suspension frequencies and short suspension travel distances can get very hard to observe.

On a real car it is pretty apparent when the car is porpoising and when it isn't. Keep in mind most real cars are quite well balanced but typically have a slightly higher ride frequency in the rear as they assume you may be hauling cargo of some kind. A good passenger car is designed with about 5 cyles per second (5 hz) higher rear frequency than front. You typically don't have the option of moving shocks around on real cars to determine spring rate like you do r/c cars either but again only serious track cars will ever worry about doing this in the real world.

I'm actually surprised it has taken until page 4 for someone to start quoting technicalities and calling out their doubts. Typically on forums, this happens far sooner and the thread goes downhill pretty rapidly. Usually when one person starts, others waiting in the woodwork will suddenly appear. Either try it or don't. It's as simple as that. People are always asking for a setup for their car and then go on blind faith that the exact setup they were given will work for them. I don't believe in this. I'd rather teach people how to arrive at their own setup and you don't easily do it through guessing.