GVM Upgrades for Your Tow Vehicle: Do You Need One?

GVM Upgrades for Your Tow Vehicle: Do You Need One?

If your tow vehicle's GVM (Gross Vehicle Mass) is the limit stopping you from towing the Mars caravan you actually want — a GVM upgrade might be the answer. But they're not always necessary, not always legal in every state, and not all upgrades are equal. Here's what to know before you spend the money.

First — Make Sure You Actually Need One

A GVM upgrade is the right answer only if GVM (or GCM that depends on it) is the actual constraint. Before assuming, do the maths:

  1. Vehicle Kerb Weight — vehicle empty, full fuel, ready to drive (manual).
  2. Add passengers — driver, family, dogs.
  3. Add accessories — bullbar, winch, drawers, roof rack, second battery, fridge, tools, recovery gear.
  4. Add tow ball download — the loaded caravan's ball weight transfers to the vehicle.

If that total is over the vehicle's GVM — you have a problem. The fix is either:

  • Reduce what you're carrying in the vehicle (often possible — recovery gear, tools, water can move to the caravan or stay home), or
  • Upgrade the GVM.

What a GVM Upgrade Actually Changes

A GVM upgrade is an engineering modification that re-rates the vehicle to a higher maximum loaded weight. It typically involves:

  • Upgraded suspension (heavier-duty springs, shocks, sometimes airbags)
  • Sometimes upgraded brakes
  • Re-rating of the tyres if needed
  • A new compliance plate issued by the engineer or upgrade kit supplier

What it doesn't change:

  • The tow rating — your braked tow capacity stays the same unless you also do a tow rating upgrade.
  • The GCM — important. Many GVM upgrades do not increase GCM, meaning the gain in vehicle weight comes off your trailer allowance.

The GCM Trap

This catches a lot of people. If your vehicle's stock GCM is 6000kg and you do a GVM upgrade that adds 300kg to your vehicle limit, your GCM is still 6000kg unless the upgrade specifically includes a GCM upgrade. Net effect: you can carry more in the vehicle, but the maximum caravan you can tow drops by the same amount.

When researching upgrades, ask explicitly: "Does this upgrade also increase GCM, or only GVM?" Some kits do both; many don't.

Pre-Rego vs Post-Rego Upgrades

Two types — and they're treated differently legally:

Pre-Registration (Second-Stage Manufacturer)

  • Done before the vehicle is first registered.
  • Treated like a factory option — the vehicle is delivered with the higher rating.
  • Generally accepted in all states without further engineering certification.
  • Tends to be cleaner from an insurance perspective.

Post-Registration

  • Done on a vehicle already registered (i.e. on your existing 4WD/ute).
  • Requires engineering certification.
  • Legality and acceptance varies by state. NSW, in particular, has had restrictions on post-rego GVM upgrades; other states are more permissive. The landscape changes — check current state rules with the upgrade supplier.
  • Insurance: some insurers may decline or restrict cover after a post-rego upgrade. Confirm with your insurer before committing.

What to Ask Before Buying an Upgrade

  1. Does this also increase GCM, or only GVM?
  2. Is this legal to register in my state, post-registration?
  3. What's included — suspension, brakes, tyres, certification?
  4. Does this affect my vehicle's factory warranty?
  5. Have you confirmed acceptance with my insurer?
  6. What's the total cost — kit, fitting, engineering, re-rego?

Get the answers in writing before paying.

Who Does Them

There are several reputable suppliers in the Australian market — Lovells, ARB OME, Ironman 4x4, Ultimate Suspension, Pedders, Tough Dog, EFS. We don't recommend a specific one because the right choice depends on your vehicle, your loaded weight target, your state and your budget.

If you'd like a second opinion before committing, talk to your nearest Mars branch — we see a lot of GVM upgrades come through and can flag any obvious mismatches.

The Conversation Worth Having First

Before spending several thousand dollars on a GVM upgrade, ask yourself the cheaper question: am I carrying things in the vehicle that should be in the van — or shouldn't be coming at all?

Sometimes the answer is yes, and an honest weight review removes the need for the upgrade entirely. Sometimes the answer is no — you genuinely need the capacity — and the upgrade pays for itself in years of legal, comfortable towing.

The Other Option

If you'd need a serious GVM upgrade plus a tow rating upgrade plus a GCM upgrade just to make the numbers work — sometimes the better answer is a different van. We have models from compact 11ft hybrids up to 16ft family vans. A different model in the range might fit your current vehicle without modification. Worth a five-minute conversation.

Related: How to Weigh Your Loaded Caravan · Can I Tow a Mars Caravan With My 4WD, SUV or Ute?· Weights 101


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