Tough Dog Foam Cell vs 40mm Adjustable Shocks
Two very different answers to the same problem. Foam Cell is the fit-and-forget upgrade that suits most four-wheel drives; the 40mm Adjustable is the tuning option for vehicles whose load changes. Here's how to work out which one you actually need.
The problem both are solving
A shock absorber turns suspension movement into heat. On a corrugated metal road it does this continuously, and the oil inside gets hot. As oil heats it thins, and in a conventional gas shock it can aerate — mixing with the pressurised nitrogen charge to form a foam that doesn't damp properly. The result is a vehicle that felt controlled at the start of the road and feels vague and floaty twenty minutes in.
That fade is what separates a touring shock from a road shock, and both Tough Dog options attack it — just differently.
Foam Cell
Replaces the pressurised nitrogen charge with a cellular foam sleeve inside the shock body. The foam accommodates oil expansion as temperature rises without allowing the oil to aerate.
- Consistent damping as heat builds
- No gas charge to lose over time
- Simple — nothing to set or adjust
- Proven, fit-and-forget upgrade
40mm Adjustable
A larger-bore body carrying greater oil volume and more surface area to shed heat, combined with external adjustment so damping can be changed to suit how the vehicle is loaded.
- Greater heat capacity from more oil
- Larger bore for better heat control
- Suits vehicles that change weight often
- Tune to the load and road
Side by side
| Foam Cell | 40mm Adjustable | |
|---|---|---|
| Damping control | Fixed, valved for the application | Externally adjustable |
| Heat management | Foam prevents aeration as oil expands | Larger oil volume and body area |
| Best suited to | Consistent load, general touring and off-road use | Load that varies — towing, seasonal touring, daily-plus-trips |
| Setup required | None | Worth setting for laden and unladen use |
| Ongoing attention | Fit and forget | Rewards adjustment as use changes |
Which one for your vehicle
Choose Foam Cell if…
- Your vehicle carries roughly the same weight most of the time — a permanent canopy and drawer setup, or a consistently unladen wagon
- You want a clear improvement over standard without having to think about it again
- You'd rather put your attention into correct spring rates, which matter more
- Most of your driving is general four-wheel driving, farm work or touring at a steady load
Choose 40mm Adjustable if…
- Your load state changes significantly — empty during the week, fully loaded for trips
- You tow, and want to firm the vehicle up for the drawbar weight without over-springing it the rest of the year
- You cover long distances on rough surfaces and want the extra thermal headroom
- You're the sort of owner who will actually use the adjustment rather than set it once and forget
Be honest about that last point
The adjustable option only earns its place if the adjustment gets used. If you'd set it once and never touch it again, put that effort into getting the springs right instead — spring rate matched to your actual load will do more for how the vehicle drives than adjustable damping ever will.
Springs matter more than shocks
Worth saying plainly: choosing between these two is a second-order decision. The first-order decision is spring rate.
Springs carry the weight and set ride height. Shocks only control how that movement is damped. A vehicle on correct constant-load springs with Foam Cell shocks will drive better than the same vehicle on under-rated springs with the most sophisticated adjustable shocks available. If you have to choose where to start, start with the springs.
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Frequently asked questions
What is a foam cell shock absorber?
A foam cell shock uses a cellular foam sleeve inside the shock body in place of a pressurised nitrogen gas charge. The foam accommodates oil expansion as the shock heats up, preventing the oil from aerating and losing damping performance — the fade that makes conventional shocks feel vague after sustained rough-road work.
Are adjustable shocks worth stepping up to?
They are if your vehicle's load changes significantly through the year, or you tow. If the vehicle carries roughly the same weight all the time, the adjustment is a capability you'd rarely call on, and your attention is better spent on correct spring rates.
Can I mix Foam Cell and 40mm Adjustable on the same vehicle?
It's not the ideal approach. Damping should be balanced front to rear, and mixing types makes that harder to get right. If you're upgrading in stages, complete an axle at a time and talk to us about the pairing.
Do these shocks need new springs as well?
Not always, but usually worth doing together. Shocks are valved to suit a spring rate, and fitting new shocks to tired original springs limits what you'll get from them. If your springs have sagged — common on older vehicles — replacing both is the better outcome.
How long do they last?
It depends heavily on use. A vehicle doing regular corrugated road work is asking far more of its shocks than one doing mostly sealed roads. Both ranges are built for sustained rough-road use, which is the point of them.
Does fitting these shocks require LVV certification?
Shock absorbers on their own don't change ride height, so replacing shocks alone isn't usually the trigger. Certification questions arise from changes to ride height and geometry. See our LVV guide, and confirm your specific build with an LVV certifier.
Still not sure?
Tell us your vehicle, how it's loaded and where you drive it. We'll tell you which option makes sense — including when the simpler one is the right answer.
Ask us Browse Tough Dog suspensionLVV certification: suspension modifications in New Zealand may require LVV certification, and what triggers it is the hardware used rather than the lift height. Read our LVV certification guide, and confirm your specific build with an LVV certifier before fitting. General information only.