What Is the 85% Rule for Towing?

The 85% rule is a UK caravanning guideline advising that a fully loaded caravan (its MTPLM) should not exceed 85% of the tow car’s kerbweight, especially for novice drivers; it is not a legal requirement but a safety benchmark designed to promote stable, predictable towing, and you must always stay within the vehicle manufacturer’s stated limits.

Where the 85% Rule Comes From and What It Applies To

In the UK and parts of Europe, clubs such as the Caravan and Motorhome Club and the Camping and Caravanning Club popularized the 85% rule as a practical safety margin for car-and-caravan combinations. It is intended to help less experienced towers choose a stable match, reducing the likelihood of sway and loss of control. The rule of thumb is guidance, not law, and it complements—never replaces—legal weight limits and the tow vehicle’s published capacities. In North America, a similar “85% rule” is not commonplace; guidance there typically centers on manufacturer ratings (GVWR/GCWR), with tongue-weight targets of about 10–15% for travel trailers.

How to Calculate Your Towing Ratio

To apply the 85% rule, you compare your caravan’s maximum laden weight to your car’s kerbweight. This ratio helps you quickly gauge whether your outfit sits within the recommended safety envelope for stability, especially in crosswinds, on inclines, and during emergency maneuvers.

1. Find your car’s kerbweight: This is the vehicle’s weight with fluids, a full tank of fuel, and standard equipment (often printed in the handbook or on the manufacturer’s data sheet).
2. Find your caravan’s MTPLM (Maximum Technically Permissible Laden Mass): This is the caravan’s legal maximum when fully loaded, usually on its VIN plate.
3. Compute the ratio: Towing ratio (%) = (Caravan MTPLM ÷ Car kerbweight) × 100.
4. Compare the result: Aim for ≤85% if you’re a novice; experienced towers may consider up to around 90%, but never exceed manufacturer limits or legal maxima.

If your calculation returns a figure at or below 85%, your combination is within the commonly recommended starting point for stability; if it is higher, consider reducing load, choosing a heavier tow car, or a lighter caravan.

Key Terms You Need to Know

Understanding a few core weight and loading terms ensures you make informed decisions and remain compliant with the law and your vehicle’s engineering limits.

• Kerbweight: The car’s weight in running order, typically including fluids and a full fuel tank.
• MTPLM (Caravan): The caravan’s maximum permitted laden mass; never exceed this.
• GVW or GVWR (Car): The car’s maximum permitted weight when loaded.
• GTW/GTW (Gross Train Weight or Gross Combination Weight): The maximum allowed combined weight of car and trailer.
• Towing capacity (braked/unbraked): The maximum trailer weight the manufacturer allows; unbraked trailers are typically limited to 750 kg in the UK.
• Noseweight (tongue weight): The downward force on the towball; must not exceed either the car’s or the hitch’s stated limit.
• Payload: The difference between MTPLM and the caravan’s mass in running order—i.e., how much you can load.

Keeping these definitions straight helps you match your outfit effectively, avoid overloading, and diagnose stability or legal compliance issues before you travel.

Why 85%? The Safety Rationale

A lighter trailer relative to the tow car reduces the trailer’s leverage in crosswinds, during rapid steering inputs, and on downhill braking. A ratio at or under 85% gives the tow vehicle more “authority” over the outfit, improving yaw stability and making snaking less likely. Experienced drivers, with careful loading and appropriate equipment, sometimes operate closer to 90%, but the margin shrinks as the ratio rises, especially in poor weather or with uneven loading.

Practical Limits and the Law (UK Focus)

While the 85% rule is guidance, legal and manufacturer limits are mandatory. Before towing, confirm your vehicle plates, handbook data, and national regulations. Here are the core compliance points.

• Never exceed the car’s stated braked towing capacity, GVW, or Gross Train Weight.
• Brakes: Trailers over 750 kg MAM must be braked; use a working breakaway cable or secondary coupling.
• Speed limits: 60 mph on motorways/dual carriageways; 50 mph on single-carriageway national-speed-limit roads when towing.
• Lanes: Do not use the right-hand lane of a three-lane motorway when towing unless directed.
• Mirrors and visibility: Fit extension mirrors if your trailer is wider than your car’s mirrors cover; failure can result in penalties.
• Licence entitlements: In Great Britain, since December 2021, a standard Category B licence allows towing of trailers up to 3,500 kg MAM, but you must still stay within your vehicle’s limits and insurance conditions.
• Dimensions and lighting: Comply with trailer width/length rules, working lights, number plate, and tyres in good condition and correct load/speed ratings.

Even with a perfect 85% ratio, breaching any manufacturer or legal limit is unlawful and unsafe; treat the legal ratings as absolute caps and the 85% rule as a conservative stability target.

Tips to Improve Towing Stability

Beyond weight ratios, good setup and loading practices play a major role in how stable and stress-free your towing experience will be.

• Load heavy items low and over the caravan axle; avoid rear-heavy packing that encourages sway.
• Aim for appropriate noseweight—commonly around 5–7% of the caravan’s actual laden weight in the UK—without exceeding the car or hitch limit.
• Use correct tyre pressures on both car and caravan; inspect tyre age and condition closely.
• Consider a stabiliser hitch or sway control device if recommended for your setup.
• Keep speeds moderate, especially in crosswinds and when overtaken by large vehicles.
• Distribute passengers and luggage sensibly in the tow car to avoid overloading axles.
• Perform pre-trip checks: lights, brakes, breakaway cable, wheel torque, and secure doors/lockers.

These practices complement the 85% guideline by reducing the likelihood of snaking and improving braking and steering response in real-world conditions.

Example: Calculating the 85% Match

Suppose your car’s kerbweight is 1,600 kg and the caravan’s MTPLM is 1,250 kg. The towing ratio is (1,250 ÷ 1,600) × 100 = 78.1%. That sits comfortably within the 85% guidance for a novice, provided the car’s braked towing capacity and the Gross Train Weight are not exceeded and all other legal requirements are met.

Bottom Line

The 85% rule is a respected guideline—particularly in the UK—for matching a caravan to a tow car to enhance stability, especially for newcomers. It is not law, and it does not override the manufacturer’s towing, axle, and train weight limits. Use it as a conservative target, pair it with careful loading and appropriate noseweight, and always verify you remain within legal and vehicle-specific constraints.

Summary

The 85% rule advises that a caravan’s MTPLM should not exceed 85% of the tow car’s kerbweight to promote stability—guidance, not law. Calculate your ratio, stay within manufacturer and legal limits, and apply good loading, noseweight, and setup practices. This approach yields a safer, more predictable towing experience, particularly for less experienced drivers.

What happens if you pull more than towing capacity?

Carrying a heavier load will force your brakes to work harder, resulting in an increased braking distance. The velocity of what you’re towing will strain the brakes and could even overtake the system, increasing the risk of an accident.

What is the 80 20 rule for towing capacity?

The 80% towing rule is less of a “rule” and more of an idea: don’t pull a trailer with a GVWR that is more than 80% of your vehicle’s maximum towing capacity. That leaves 20% of your towing capacity left for other cargo like passengers, baggage, etc.

What is the biggest trailer you can tow without a licence?

You can tow a trailer that weighs up to 3,500kg MAM .

What is the rule of thumb for towing?

The towing rule is not to haul a load heavier than 80% of your towing vehicle’s towing capacity. Providing a decent margin of error in the event of miscalculating your trailer and its load, the 80% rule is a sensible rule of thumb to follow.