To get rid of that Pogo effect, you need to increase the Frequency of the springs [cycles per second], And the way to do that is with stiffer rating and a lower spring load. [ Translated = Higher lbs/in but shorter static height ]
If the "pogo effect" he refers to is bounciness of the suspension, then it means it's underdamped.
If you drove your "grocery getter" around a road racing circuit at 30 mph you would wonder why suspension is even needed, but crank that up to 100+ mph and a bump that you didn't even notice before will start to bottom out the suspension etc.
A quick succession of such bumps could cause the suspension to bottom in that manner, I suppose, but a single bump will not unless there is insufficient travel to absorb it. An increase in spring rate will prevent the suspension from bottoming, of course, but it will also (if set too high) prevent the suspension from properly absorbing the bump in the first place, and cause greater force to be transmitted through to the cabin and to the tires (Newton's Law). But a change of force to the tires changes the grip of the tires, which is what you do
not want if you're after predictable handling.
You're absolutely right that the proper spring rate is critical. The main issue is that you don't get a variable spring rate that depends on the characteristics of the bump as seen by the car (well, actually, you do to some extent since the dampers factor into this, but the dampers cannot reduce the compression forces of the spring and cannot increase the rebound forces either), so you end up having to compromise, to find a spring rate that is optimized for the most common case under the circumstances the car is subject to.
The faster you go, the faster the wheels travel up and down over bumps [higher frequency] ,so stiffer springs are needed.
This is true, but note that there is no difference between a wider bump at higher speed and a narrower bump at lower speed, if the bump height is the same for both. The suspension can't tell the difference.
Even so, what you say here is most certainly true, but chances are this isn't what the OP is running into.
If you simply "upped the valving" on a set of shocks, it would simply slow down the frequency on rebound [or droop] and the tyres would have a tendency to skip over the tops of bumps.
If they're overdamped at that point, yes.
The shocks should be matched to the springs, so unless you have a crystal ball you should choose the correct springs first.
Exactly right. But note that "correct springs" depend on the application. There is a massive difference between a dual-duty (street + noncompetitive track) car and a single-purpose competitive track car. For the latter, you can optimize the spring rates to accommodate the demands of the track. The former requires that you compromise even more than you're already compromising with a track-only car. That makes the choice a more difficult one in the former case, because you then end up having to decide where that compromise point should be, and that is very much a matter of preference.
For instance, I'm on what amounts to stock springs, and yet have found that my car behaves very nicely on the track. But then, I'm on street tires as well. My car is both a daily driver and a track toy for me, and obviously the "daily driver" role dominates in terms of total seat time. That doesn't prevent the car from handling the track surprisingly well.
While the bumps that one does encounter on the track are encountered at higher speed than what a street car sees on the street, most tracks are significantly smoother than most streets, which is why you can get away with substantially stiffer springs on the track.
Now on the subject of Koni's vs Bilsteins [they are both good shocks]
The Koni "twin tube" is more resilient to damage from rocks etc, but the Billy's don't lose as much dampening effect when they get hot.
What I wonder is how much of a real difference there is in practice, particularly when one is on springs with roughly stock rate (which will be essentially all springs that one would pair the Konis or the Bilsteins with). I'd argue that the street is a much stronger workout for the dampers than most tracks, because most tracks are relatively smooth while many streets are just terrible, and the suspension is moving around a lot more, and exercising the dampers a lot more, when driving down a typical street than it is when driving on the track.
Bilsteins being a monotube shock have a larger piston area, and a floating piston to keep the oil and the gas separated [they don't aerate the oil and lose dampening]
All other things being equal, yes. My understanding is that Koni uses a type of oil that is highly resistant to aeration, so while it may still be subject to that, it apparently isn't to the degree that one might otherwise expect.
Frankly, I know of no objective head to head comparison between these dampers. And that's a shame, because it would be very useful to some to know how much of a difference there really is between them when all is said and done.
Monotube shocks are superior for racing. Koni also makes monotube shocks, but these Koni Yellows are twin tube
I'd go with the Bilstein monotubes
The only major reason to go with the Konis over the Bilsteins is for the adjustability. But that is not an insignificant difference. The adjustability of the Konis means you can exactly (or nearly so) match its rebound to the springs (but note that you'll need to get your dampers dynoed for this to work -- you'll be doing it "by feel" otherwise, which may work out nicely if you know what you're doing), while the Bilsteins will merely be "in the ballpark" so to speak. Being "in the ballpark" might be sufficient, and indeed almost certainly is for most people. But the major advantage to the Konis is that you can tune the front versus rear transition characteristics of the car to your liking. This won't have any effect on mid-corner behavior but can substantially effect corner entry and exit. With the Bilsteins, you get what you get and that's that.
As you say, they're both good, so it ultimately comes down to a matter of preference. I've been immensely satisfied with my Konis, for what little that may be worth. As someone who drives his car daily and on the track, they've served me extremely well over the past three years.
In any case, given the OP's complaints, I stand by my original recommendation: change the dampers first, and
only the dampers. Then determine if that's sufficient. If it's not, then determine how it's not sufficient and make the next (single) change on that basis. Lather, rinse, repeat until you get what you want.
