Hello everyone!
Out of the blue, let me ask you this: have you been adjusting your damper settings?
Changing the damping force of your dampers can completely transform the way a car feels to drive.
Increase or decrease the damping force, and the speed of the car’s body motions—things like pitching under braking and body roll in corners—changes noticeably.
But finding the “right” damping setting isn’t easy. The ideal amount depends on the track you’re driving, and it also comes down to the driver’s personal preference.
Another thing that often causes confusion is how changing damping force affects tire grip. The mechanism behind it is surprisingly complicated, which makes it easy to misunderstand.
The other day, I was watching YouTube. And no, not the kind of videos you might be thinking of—I was watching a motorsport-related video.
In it, there was this rather intimidating-looking guy happily talking about damper tuning. He said something that caught my attention.
“How do you tell whether stronger or weaker damping is better? For example, if the rear of the car becomes unstable under heavy braking when entering a corner, you increase the rear damping. By increasing the rear damping, the rear doesn’t lose load as easily under braking, making the car more stable.
I used the word ‘load’ because it’s easier for drivers to understand, but from a mechanic’s point of view, it’s not exactly what’s happening.”
So what does he mean by that?
Load transfer is simply the change in the load acting on each tire. It is determined by four factors:
- Vehicle weight
- Center of gravity height
- Acceleration acting on the vehicle
- Wheelbase (or track width, depending on the direction of the load transfer)
For example, imagine increasing the damping force to infinity so that the dampers effectively become solid bars that cannot compress or extend at all. Even then, braking still transfers load from the rear tires to the front, and acceleration still transfers load from the front tires to the rear.
As long as those four factors remain the same, the amount of load transfer essentially stays the same as well. (Strictly speaking there are tiny effects caused by energy stored and released by the springs, friction, and so on, but they’re negligible here.)
Since changing spring stiffness or damping force changes how much and how quickly the suspension moves, it’s easy to assume that if the suspension moves more slowly, load transfer must also happen more slowly.
However, that’s not actually the case.
The load transfer generated by the relationship between the tires, the road surface, and the vehicle’s center of gravity is a separate physical phenomenon. Suspension movement is the result of internal forces within the vehicle, so it doesn’t directly change load transfer itself. (Again, we’re ignoring very small secondary effects such as slight changes in center of gravity height or wheelbase caused by suspension travel.)
Think about it this way.
If increasing damping force really slowed down load transfer itself, then making the damping infinitely stiff would mean load transfer also became infinitely slow. You could stand on the brakes, yet the load transfer would never really finish—in other words, almost no load transfer would occur.
But that’s obviously not what happens.
The moment you hit the brake pedal, load transfer occurs immediately. What changes is the speed of the car’s pitching motion.
The only time load transfer itself becomes slower is when the change in acceleration becomes slower—for example, when you apply the brakes or throttle progressively instead of all at once.
And yet, anyone who’s adjusted damper settings knows that the handling definitely changes.
So what exactly is causing that?
Explaining it properly would probably take an entire book, so instead I’ll simply list a few of the factors that are involved.
– Tire contact
If the damping is either too stiff or too soft, the suspension can’t follow bumps and uneven pavement properly, reducing tire contact with the road.
Poor front tire contact tends to increase understeer, while poor rear tire contact tends to increase oversteer.
– The rate of change of the roll axis
Changing the damping force changes the speed of the car’s pitching motion. In corners where pitching has a noticeable influence, this also changes the dynamic roll axis—that is, the position and angle of the roll axis at different points through the corner.
Because the angle of the roll axis affects how load transfer is distributed between the front and rear, and because tire cornering force does not increase linearly with load, a roll axis that leans further forward tends to move the balance toward oversteer, while a less forward-leaning roll axis tends to move it toward understeer.
I’ll leave out the effects of roll axis position for now.
– The rate of change of track width
Changing the damping force also changes the speed of pitching and rolling, which means the dynamic track width—the effective track width at different points around the course—changes as well.
The exact behavior depends on the suspension design, but generally speaking, if the front track increases more than the rear, the balance tends toward oversteer. If the rear track increases more, it tends toward understeer.
(That said, while the track width is actually changing, the tires are generating cornering force by pushing against the road surface, so depending on the situation, the understeer/oversteer tendency can even reverse.)
– The rate of change of alignment
Since changing the damping force changes the speed of pitching and rolling, it also changes the dynamic alignment—toe and camber at different points around the course.
Again, the exact behavior depends on the vehicle, but if those alignment changes increase front tire cornering force, the balance tends toward oversteer. If they increase rear tire cornering force instead, it tends toward understeer.
Earlier I skipped over the effects of roll axis position, but things become even more complicated when bump and rebound are considered separately, since they also affect the height of the center of gravity and the position of the roll axis, including its lateral position.
To be honest, I haven’t looked into that area in enough detail myself, so I don’t have a complete understanding of it.
So, to put it very roughly, when the car pitches forward it tends toward oversteer, and when it pitches rearward it tends toward understeer.
That’s a huge oversimplification, of course.
And there are also cases where that doesn’t apply.
In the video, he said that if the rear becomes unstable under heavy braking, you should increase the rear damping.
That’s often true, but only up to a point. If the road surface is rough and you make the damping unnecessarily stiff, the rear can become unstable again.
At Takasu Circuit, for example, damping adjustments usually have a bigger effect in corners like Getchan or Grip End than they do in corners like Kageyama. It really depends on the type of corner.
Then again, even that depends on the car itself. A car with a lot of suspension travel won’t respond the same way as one with very little travel.
As you can see, it’s a surprisingly complicated subject.
So, explaining all of this to a driver is extremely difficult.
That is why, in most cases, it is probably better to simply say:
“Increasing rear damping keeps the rear from losing load as easily, which makes the car more stable.”
It may not be the most physically precise explanation, but it is much easier for a driver to understand.
Interestingly, if you ask ChatGPT to explain this mechanism, it will usually give you a similar answer at first.
But if you respond with something like, “I don’t care how humans perceive it—just explain the actual physical changes,” and keep pointing out the inconsistencies, it eventually switches to a more accurate explanation.
If you can get ChatGPT to give you the answer: “Damper adjustments do not directly change tire load transfer itself. Instead, they influence tire grip characteristics through changes in vehicle behavior and suspension geometry” — then congratulations, you are probably just as much of a suspension geek as I am.
Anyway, the basic purpose of damping adjustment is to improve tire contact with the road.
So ideally, understeer and oversteer should be adjusted through things like roll stiffness balance and front/rear ride height balance.
That said, can you really keep the roll stiffness and ride height balance at a perfect 100% match for every course condition? That’s not exactly easy.
Especially in an environment like gymkhana, where you often have to make adjustments on the spot, you can’t always afford to say, “Let’s first optimize everything perfectly.”
So for those of you who are already deep into setup work, good luck fine-tuning your cars.