Fox launched its new Grip X and Grip X2 fork dampers in 2025 with a great deal of hype and some lofty promises. ‘Support without the harshness’ was the big sell, backed up by a new damper with a larger diameter valve packed with 300% more shims. More and bigger – these are easy concepts to comprehend. Larger pistons allow more oil flow, and additional shims give more tuning possibilities with extra fidelity.

But there was one term I kept hearing in all the presentations and conversations with the Fox engineers and suspension tuners that I didn’t understand. ‘Pressure balanced-this’ and ‘pressure balancing-that’ was being bandied around at every opportunity. Clearly it was important in the quest for the ultimate suspension fork performance, but what did it mean? And why has Fox made such an effort to integrate this procedure into its Grip X and Grip X2 damper development?

Fox introduced a suite of new dampers last year, including the Grip X2, Grip X, and Grip SL.

What is pressure balancing?

For the answer, I turned to Ariel Lindsley from the product development and R&D department at Fox. “What you’re doing with pressure balancing is creating a certain amount of damping from the base valve (at the head) and a certain amount of damping at the main piston – which is the one that moves up and down through the oil. We’re trying to keep the pressure behind the piston from changing drastically as it moves.”

Ariel Lindsley’s job is to make sure Fox’s suspension products ride as well as possible.

The first thing to take away from that explanation is that pressure balancing in this context has nothing to do with the air spring. Which, to make things extra confusing, has its own pressure balancing between the positive and negative air chambers. Here, pressure balancing refers solely to the damper, and how the pressure changes above and below the main piston as the oil is displaced.

In this Fox Grip X fork damper cutaway you can see the main piston that moves up and down inside the damper tube, as well as the base valve at the head of the fork.

What are the advantages of pressure balancing a damper?

Pressure balancing aims to reduce hysteresis in order to make the damper more responsive and increase grip, while also avoiding cavitation (when air is introduced into the damping fluid). In this context, hysteresis describes the lag in response at the damper to a bump input. As you can imagine, any delay in damper response is undesirable, as it means the forces are being transmitted to the rider rather than absorbed by the suspension.

A Grip X2 damper has a stack of 23 shims at the base valve (the gold pyramid shape).

But get the pressure balancing right, and lower the hysteresis, and you’ve got a fork or shock that can react more quickly to bumps, track the ground better, and create more grip – all with no reduction in control because the damping is still there.

“There’s a lot of little things we’ve done to the [Grip X, Grip X2, and Float X2] to improve that valve response time, which overall, just basically decreases hysteresis. The shock reacts in direction changes faster. Damping turns on and off quicker, and that controls your contact patch better, or your grip better. More sensitivity equals more grip. Effectively, that’s what we’re chasing.”

This cutaway shows the damper installed in the fork (a Fox 38 Factory Grip X2). As the fork compresses, pressure builds above the main piston head and reduces below. Ideally the pressure change should be equal both sides.

“It’s really not something completely novel. And we’re not the only ones in the world who’ve done it”, Lindsley told me. But it’s not something all mountain bike suspension brands do; “it takes more work. You have to have the tools to measure it.” By that he means you need a shock dyno and sensors installed at various locations throughout the damping circuit to measure the pressure in real-time at really high sampling rates.

Fox’s latest MY26 Float X2 shock is also pressure balanced.

How do you pressure balance a damper?

So how do you pressure balance a damper? It’s not a straightforward question to answer given the technicality of a damping circuit, but in essence, the suspension tuner is trying to even out the change in pressure across the rebound and compression circuit. Ideally they want to change by the same amount.

From top to bottom; New Fox Grip SL damper, Fox Grip X2, Fox Grip X, old Fox Grip 2, and old Grip damper.

“Let’s say you didn’t have a base valve, and you just let the oil flow through the valves. The main piston – the dynamic piston – would have no reason for those valves to open. And so there would be a vacuum created behind that piston, and that vacuum is very bad. That’s going to create cavitation. So you’re trying to keep enough pressure on those valves that they open soon enough that you don’t get a low pressure behind the shock. We need the base valve to do enough work and create enough force to make the main piston valves open, without creating a low pressure. So what you want to do is try to keep the pressure nice and even throughout the shock, no matter what it’s doing in this movement.”

If you still don’t understand what pressure balancing is, and I don’t blame you, it’s worth reading this explanation from Penske Racing Shocks. But equally, cutting through the complex fluid dynamics and understanding what the advantages are on the trail is the key for most riders. “We keep spitting out the word pressure balance, valve response time, low hysteresis”, Lindsley tells me. “And it does sound like, what is this wizardry? Is it just a bunch of words? It would be more fun if I got to take people out and go, ‘okay, here’s a shock that’s just way over-valved at the base valve’. And let them ride it down the hill. Then take them back up the hill again, and put on a shock that has the exact same amount of damping, but it’s perfectly pressure balanced. That would be a much more fun way to do it. We had to prove that to ourselves, and when we did that, it was pretty obvious that this was the route to take.”