A second spare is smart insurance for remote travel, but bolting a 35kg wheel to the back of your truck can quietly make it unroadworthy. Getting it right means thinking about three things: visibility (plate and lights), dimensions (overhang), and weight (axle and GVM). None of these is hard to meet — you just have to plan for them.

Where can you mount a second spare?

Location	Pros	Watch out for
Rear bar / wheel carrier	Easy access, protects the rear, swings clear	Blocks plate & lights; adds rear-axle weight; needs quality carrier
Roof rack	Frees the rear	Raises centre of gravity; hard/dangerous to lift down; roof load limit
Ute tub / cargo area	Low, secure, hidden	Loses payload space; must be tied down properly
Under-body (factory)	Out of the way	May not clear upsized tyres; awkward when bogged

Most tourers choose a rear wheel carrier for a heavy second spare because it’s the easiest to lift on and off. That’s also the option with the most legal detail attached.

Keeping the number plate and lights legal

Across Australia (following the Australian Design Rules), your rear number plate must be mounted upright, roughly between 300mm and 1300mm off the ground, and be legible within a 45-degree arc from 20 metres. It must also be lit at night by a working plate light. A spare wheel on the rear bar commonly blocks both — so the fix is a compliant relocation bracket that repositions the plate and light clear of the wheel, plus making sure your tail-lights, brake lights and indicators aren’t obscured. If they are, add supplementary lights. This is exactly the issue 4WD specialists like Club 4X4 flag most often with rear carriers, and it’s worth confirming with your state road authority since the fine detail differs between states.

Rear overhang and dimensions

A wheel carrier that sticks a long way past the towbar can breach rear overhang rules — broadly, rear overhang is limited to a proportion of the wheelbase (commonly around 60%, but this is set by the rules, not by us). A big carrier plus a wheel plus jerry cans can push you over. It can also affect your departure angle and, if you tow, how the carrier interacts with the towbar and coupling — see tyre rules for towing. Measure before you build, and if in doubt get it checked.

Weight: the limit people forget

A full-size all-terrain spare on a steel rim can weigh 30–40kg, and it’s hanging right at the back — the worst place for a heavy load. That eats into your rear axle limit (GAWR) and your GVM, especially once the tank’s full and the fridge is loaded. If you’ve done a GVM upgrade, know your new numbers; if you haven’t, weigh the loaded rig. Overloading the rear also changes handling and braking. And make sure the spare itself is up to the job — correct spare tyre pressure and, on a modified truck, a spare that matches your all-terrain tyres.

Secure it properly

Any spare must be restrained so it can’t come loose in a crash or heavy corrugations — a rated carrier and locking mechanism for external mounts, or proper tie-downs (not a stretchy occy strap) for a tub-mounted wheel. A loose 35kg wheel is a projectile.

A quick pre-trip legal checklist

Before you head off with a second spare fitted, run through this:

• Number plate visible within a 45-degree arc from 20m, upright, and between roughly 300–1300mm off the ground.
• Plate light working and lighting the plate at night.
• Tail-lights, brake lights and indicators not blocked — add supplementary lights if the carrier covers them.
• Rear overhang within the limit for your vehicle (measure it).
• Loaded weights under your rear axle rating and GVM — weigh the rig fully loaded.
• Carrier and wheel rated, secured and locked, with no rattle on corrugations.

If anything’s borderline, a quick chat with your state road authority or a certifier before the trip is cheaper than a defect notice on the way home.

FAQ

Is it legal to cover my number plate with a spare tyre?

No. The plate must stay visible within a 45-degree arc and lit at night. If a rear spare blocks it, fit an ADR-compliant relocation bracket and plate light.

Do I need an engineer’s certificate for a rear wheel carrier?

Often no for a bolt-on carrier that keeps you within limits, but requirements vary by state and by how it attaches. Confirm with your road authority or a certifier — this is general information, not a compliance ruling.

How much rear overhang is allowed?

Rear overhang is capped as a proportion of the wheelbase under the vehicle standards (commonly around 60%). Measure your setup and check the current figure for your vehicle category with your state authority.

Can carrying a second spare overload my 4WD?

Yes — a heavy spare at the rear can push you over your rear axle rating or GVM once loaded. Weigh the rig and stay within your placarded limits.

Bottom line: A second spare is legal to carry when the number plate and lights stay visible and lit, the setup respects rear-overhang limits, and the extra weight keeps you inside your axle and GVM ratings. The details differ by state, so measure, weigh and confirm with your road authority or an engineer before the big trip. Decide first whether you even need two spares.