What 25% Sag Actually Means (And Why It Matters)

Posted by Flatout Tech on Apr 23rd 2026

If you’ve looked through any of our setup material, you’ve probably noticed one number keeps showing up: 25% sag.

That’s not by accident. It’s not a rough guess or a “good enough” starting point either. It’s a target we use because it puts the suspension in the right part of its travel where everything actually works the way it’s supposed to.

The problem is, most people either don’t measure sag at all, or they think they understand it but end up setting it wrong. And when that happens, the suspension never really feels right, no matter how good the components are.

So what is sag, really?

At its simplest, sag is how much the suspension compresses under the weight of the vehicle.

There are two positions that matter:

Suspension fully extended (wheel off the ground)
Suspension at rest (vehicle sitting normally)

The difference between those two is your sag.

When we say “25% sag,” we’re saying the suspension should settle about a quarter of the way into its total travel just sitting there.

Why 25%?

Because it gives you balance.

At that point in the stroke:

You’ve got plenty of room left to absorb bumps
You still have enough droop for the tires to stay planted over uneven ground
The shock is working in the part of the stroke where it’s actually effective

Go too far one way or the other, and you start giving something up.

Let’s put some numbers to it

Say your suspension has 8 inches of total travel.

25% of that is 2 inches.

So ideally, the suspension settles 2 inches under the weight of the vehicle. That leaves you with:

6 inches to compress into bumps
2 inches of droop to follow the road

Now think about a spring.

If you’ve got a 12-inch spring and it settles down to 9 inches at rest, that’s 3 inches of compression. That’s right around that 25% window, and that’s exactly where you want to be.

How to actually measure it

This is where things usually go sideways.

You need to take two simple measurements, but they have to be done correctly.

First, get the suspension fully extended. Jack the car up so the wheel is off the ground and everything is at full droop. Pick two fixed points, one on the chassis and one on the suspension or wheel, and measure that distance.

Then set the car back down on the ground and measure the same two points again.

The difference between those numbers is your sag.

That’s it. No guesswork, no eyeballing.

What happens when you get it wrong

This is where sag actually starts to matter.

If the car is sitting too low in the travel, meaning too much sag:

You run out of compression travel quickly
It feels soft at first, then harsh when you hit something bigger
Bottoming out becomes a real issue
The car can feel loose or sloppy

On the flip side, if the car is sitting too high with not enough sag:

You lose droop travel
The suspension tops out over bumps
The ride gets stiff and jittery
The tires don’t stay planted the way they should

That second one is extremely common, especially when people crank preload just to get more lift.

It might look right, but it drives worse.

Where preload actually comes in

Preload is there to help you dial in sag. That’s its job.

It’s not there to set ride height.

If you need to change how much the suspension is compressing under weight, you adjust preload or spring rate. Once you’ve got sag where it should be, that’s when you fine-tune ride height using the shock body.

Mix those two things up, and you end up chasing your tail.

Why this matters more than people think

Sag is one of those things that seems minor until you get it right. Then everything starts to make sense.

The ride feels more controlled. The car is more predictable. It handles bumps without feeling harsh or unsettled. Off-road, it keeps traction instead of skipping across the surface.

It’s not magic. It’s just the suspension finally working in the range it was designed for.

The bottom line

If something feels off, this is one of the first things worth checking.

Not because it’s complicated, but because it’s so often overlooked.

You can have a really well-designed suspension, but if it’s sitting in the wrong part of its travel, it’s never going to feel the way it should.

Get sag right, and everything else starts to fall into place.