What can you learn from a damping ratio plot?

[SorryTires]

Hopefully some of the suspension gurus can help me out here. I made a plot of front end damping ratio vs shock velocity for the stock set up and some aftermarket coilovers hoping to make a comparison but i now realize i have no idea what to make of it.

What does having a less over-damped low speed rebound shock do to the cars behaviour?

Having more low speed compression should mean the car will transition quicker and be more responsive right?

What else can you tell from this plot?

[RJasonKlein]

Good questions, and I’m looking forward to seeing the responses you get.

[Racecomp Engineering]

The "internet numbers" (which aren't perfect) you often see are a 60-70% critically damped, or a 0.6-0.7 damping ratio. If you dig in a little bit, this refers to the low speed piston velocity, or up to about 2 inches per second. After that, a slightly lower damping ratio is often preferred for higher piston speeds (maybe 30%). The idea being that a higher damping ratio is good at lower piston speeds (body roll), while less is preferred for bigger bumps and higher piston speeds. All of this refers to rebound damping, with some recommending maybe 2/3 as much compression damping.

So in a plot like you posted, you'd want to see that particular idea represented by a line that starts out around 0.65 and then smoothly dip to around 0.30. That would indicate a digressive damper.

There are MANY other things to think about. Swaybars matter too, and damping ratio in ride vs bump are separate considerations that require compromise since you only have 4 dampers. You might want different ratios at the rear vs. front of the car. A front engine, rear wheel drive car might perform better with a different set up than a front wheel drive car or all wheel drive car.

Most of the time you'll see numbers higher than that 65% critically damped. Sometimes less, even on a racecar. Different companies have different "philosophies"....maybe lots more compression than rebound, maybe tons of rebound. Some of them are IMO more correct than others.

- Andrew

[jamal]

Originally Posted by SorryTires

Having more low speed compression should mean the car will transition quicker and be more responsive right?

Actually, the opposite. When loaded, an undamped spring will compress the fastest, and the damper is slowing that down. Too much low speed compression will cause the car to take longer to settle into steady state cornering.

From most of the plots I've seen you kind of need a 3-way to go too far on the low speed comp. Lot of the more inexpensive and 1-way shocks don't have much going on down there.

[SorryTires]

Originally Posted by Racecomp Engineering

There are MANY other things to think about. Swaybars matter too, and damping ratio in ride vs bump are separate considerations
- Andrew

This is one thing that always bothers me, no one ever sais if their talking about things in roll or bump and you get pretty different numbers depending which you look at. So would you theoretically want a ~0.6 damping ratio for both or does that apply to one more than the other? I know this is a pretty simplistic view of things and im sure the real answer is "it depends"

Edit: just realized i didnt even say which im refering too the plot i posted does not include the sway bar

[jamal]

Originally Posted by SorryTires

This is one thing that always bothers me, no one ever sais if their talking about things in roll or bump and you get pretty different numbers depending which you look at. So would you theoretically want a ~0.6 damping ratio for both or does that apply to one more than the other? I know this is a pretty simplistic view of things and im sure the real answer is "it depends"

Edit: just realized i didnt even say which im refering too the plot i posted does not include the sway bar

For ride, a lower damping ratio is more comfortable. So you would want the "0.6 ratio" to apply mostly in roll when you are actually cornering.

But swaybars of course will cause the opposite to happen. Just having swaybars means the ratio will always be higher in ride vs roll.

Probably why the fancy cars have active dampers and hydraulic roll control and whatnot.