Towing Mirrors for Caravans & 4WDs: the 85% Rule and What SA Law Really Requires

By the Car Mirror Man team · Mobile mirror specialists, Adelaide metro · Updated 2026

Search “towing mirrors caravan” and you’ll find a lot of confusing advice — especially the idea that the “85% rule” is a mirror law. It isn’t. If you’re an Adelaide family hitching up for a run to the Flinders Ranges, a weekend on the Fleurieu, or a lap along the Murray, this guide sorts the myth from the law: when towing mirrors for a caravan are actually a legal must, what the 85% rule genuinely refers to, the different mirror types, and how to get the right ones fitted without paying for parts you don’t need.

Do you need towing mirrors when towing a caravan?

The short answer: usually yes — but not because a law names “towing mirrors” specifically. The real requirement is about clear vision behind you. Under the Australian Road Rules that South Australia adopts, a driver must be able to clearly see the road and traffic to the rear of the vehicle, and a vehicle must be fitted with mirrors that give that view (National Transport Commission, Australian Road Rules). Your standard door mirrors are designed to see down the sides of your car — not down the sides of a caravan that’s wider and taller than the tow vehicle.

So the test is simple: if the caravan blocks the rearward view your factory mirrors normally give you, you must fit extension (towing) mirrors so you can still see clearly down both sides. For nearly every caravan — and most box trailers, boats and camper trailers wider than the car — that means towing mirrors are legally required. If you’re towing something narrow (a small motorbike trailer, say) that you can still see clearly past, extension mirrors may not be needed.

Rear-vision-mirror fitment on new vehicles is governed nationally by the Australian Design Rules for rear vision (Dept of Infrastructure & Transport, ADRs) — but keeping a clear view while towing is the driver’s responsibility.

The 85% rule — what it actually is (and what it is NOT)

Clearing up the biggest myth

Here’s the correction that matters: the 85% rule has nothing to do with mirrors. It’s a towing-weight guideline. The widely recommended figure is to keep your fully loaded caravan or trailer at or below 85% of the tow vehicle’s kerb (tare) weight. Stay under that and the van is far less likely to overpower the car and start swaying or “snaking” at highway speed — a leading cause of caravan rollovers (NRMA, towing capacity explained).

Two things people constantly get wrong about it:

• It is a safety guideline, not a law. The 85% figure comes from motoring and caravan bodies as best practice. What’s legally enforceable are the manufacturer’s rated limits — braked towing capacity, GVM, GCM and tow-ball mass — and you must stay within those (RAA, towing advice). The 85% rule sits inside those legal limits as an extra safety margin.
• It is about weight and stability, not vision. It says nothing about mirrors. The reason both come up together is that people research “towing legality” and mix the two up.

Towing mirror law in SA: what South Australian rules actually require

South Australia applies the Australian Road Rules through the state’s road traffic legislation, and the SA Driver’s Handbook is clear that when you tow, you must be able to see clearly to the rear and down both sides of what you’re towing (MyLicence SA, Driver’s Handbook — Towing). In plain terms:

• If your caravan or trailer obscures the view from your normal mirrors, you must fit towing mirrors that restore a clear rearward view.
• The extension mirrors must not stick out further than needed to give that view, and shouldn’t create a hazard to pedestrians or cyclists.
• Driving with an obstructed rear view can leave you exposed to a defect notice or fine — and, far more importantly, it’s dangerous when you’re changing lanes on the South Eastern Freeway or merging onto the Port Wakefield Road with a van behind you.

Bottom line: SA law doesn’t hand you a checklist that says “fit towing mirrors”. It hands you a duty — see clearly behind you — and for a caravan, towing mirrors are how you meet it.

Choosing towing mirrors for your caravan or 4WD

There are three broad ways to get a legal, clear rear view when towing a caravan — and they suit different drivers. Extension mirrors have been around as long as people have towed wide loads (Wikipedia, wing mirror); the difference today is how well they stay put and how much tech they carry.

Why this matters for SA touring: the Flinders, the Riverland and the Fleurieu mean long highway stints, gravel edges and chilly early starts. Powered, heated tow mirrors that hold a steady, demisted view earn their keep — a clip-on that’s shaking itself loose on the Barrier Highway doesn’t.

“The 85% rule keeps the van behind you steady. Towing mirrors keep the traffic beside you visible. You need both — they solve different problems.”

The DIY reality

Plenty of drivers try to save money with the lowest-cost clip-ons off the shelf, only to find they can’t see a thing on a corrugated back road, or the strap has chewed the paint on their factory mirror. Getting the right mirror matched to your exact vehicle — and, if it’s a factory powered tow mirror, fixing only the broken part — is a once-or-twice-in-a-lifetime job most people are better off leaving to a specialist. It’s cheaper than buying the wrong thing twice.

Getting the right towing mirrors fitted in Adelaide

This is where being a mirror specialist matters. If your 4WD or ute already has factory extendable tow mirrors and one has a cracked face, a dead heater, a failed fold motor or a broken indicator, most places quote you a whole new assembly. We don’t default to that. We diagnose the exact fault and replace only what’s broken — often just the glass. That’s the lowest cost option, and it’s usually the better repair too.

Those bands are indicative — the exact figure depends on your model. For the full breakdown across every mirror type, see our side mirror replacement cost guide. We can offer the lowest cost option because we’re mirror specialists: we custom-cut glass, work across a broad supplier network, and repair over replace wherever possible. And all our work is guaranteed.

Adelaide coverage: our mobile service covers the Adelaide metro — Elizabeth to Noarlunga, the CBD to the Hills, Salisbury, Modbury, Golden Grove, Norwood, Glenelg, Marion and Port Adelaide. Heading off from regional SA — the Flinders, the Riverland, the Yorke or the Limestone Coast? We don’t travel there, but we can ship the correct mirror glass or part to you for local fitting. Contact us for parts pricing.

What to do next

• Check your van’s loaded weight against the 85% guideline — and against your car’s legal towing limits.
• Sit in the driver’s seat with the van hitched. Can you see clearly down both sides? If not, you need towing mirrors.
• Photograph any cracked, foggy or faulty existing tow mirror and send it through for a fixed quote — we’ll tell you if it’s a glass-only fix.

Related reading: Towing & 4WD mirror replacement in Adelaide · Toyota HiLux mirror replacement Adelaide · Car Mirror Man Adelaide

About Car Mirror Man. We’re a mobile car side-mirror specialist serving the Adelaide metro and cities across Australia. We come to you and fix only what’s broken — repair-first, custom-cut ADR-compliant glass, genuine-quality parts, and all work guaranteed. Operated under Car Mirrors Australia (Motor Mechanic Licence MVTC161669).

Towing mirror FAQ

Sources

1. Government of South Australia — MyLicence, The Driver’s Handbook: Towing. mylicence.sa.gov.au/the-drivers-handbook/towing
2. National Transport Commission — Australian Road Rules (rear vision / clear view). ntc.gov.au/laws-and-regulations/australian-road-rules
3. Australian Government, Department of Infrastructure, Transport, Regional Development and Communications — Australian Design Rules (rear vision mirrors). infrastructure.gov.au — Australian Design Rules
4. NRMA — Towing capacity explained (the 85% guideline). mynrma.com.au — towing capacity
5. RAA (Royal Automobile Association of South Australia) — Towing advice. raa.com.au — towing
6. Wikipedia — Wing mirror (extension / towing mirrors). en.wikipedia.org/wiki/Wing_mirror

Sources

1. Government of South Australia — MyLicence, The Driver's Handbook: Towing
2. National Transport Commission — Australian Road Rules
3. Dept of Infrastructure & Transport — Australian Design Rules (rear vision mirrors)
4. NRMA — Towing capacity explained (the 85% guideline)
5. RAA (Royal Automobile Association of SA) — Towing advice
6. Wikipedia — Wing mirror (extension / towing mirrors)