The curtain-sider is the workhorse of UK general haulage precisely because it loads from the side - but the feature that makes it convenient is the one that makes it dangerous when misunderstood. A standard curtain is a weather seal, not a load restraint. The government’s load securing guidance sets out what actually holds the load in a curtainsider, and the answers are more systematic than “throw a couple of straps over it”.
The cleanest way to secure a load is to make the vehicle body do the work. Positive fit secures a load inside a trailer or vehicle body strong enough to withstand the forces of the journey - the guidance names the BS EN 12642 XL standard, which rated curtains are built to. But positive fit has strict geometry. The load should fill the load bed with minimal gaps, and to count as effective it must be against or within 30cm of the headboard, loaded tightly along the length with no gap or cumulative gaps over 30cm, within 30cm of the rear doors, and within 8cm of either side. Where gaps cannot be filled - with empty pallets, timbers or similar - the load must be secured as in any non-XL rated vehicle. Cylindrical loads such as paper reels can achieve positive fit when the extremity of one reel or two side by side is within 8cm of the vehicle side. In other words: an XL body only restrains a load that genuinely fits it, to the centimetre.
For loads that do not fill an XL body - or for vehicles built to the lower L rating - the restraint is equipment, and the guidance gives curtainsider-specific methods. Buckle straps - the hanging black straps - and internal nets fitted to roof rails can contain loads on standard curtainsiders, with a hard limit: the individual load items or stacks being secured can weigh up to a maximum of 400kg. Buckle straps and internal nets must not be used for items or stacks over 400kg. Where the load does not fill the load bed, the last row should be secured with a ratchet strap with the load blocked to fill the gap, or buckle straps or an internal net used to form a rear bulkhead.
Headboards and bulkheads earn their keep under braking: where the headboard forms part of the securing system, the load must be placed in contact with it or within 30cm wherever possible, to stop forward movement under braking. Where that is impossible - axle weights being the classic reason - additional methods must prevent forward movement: an obstacle such as stacked timbers strapped to the vehicle, blocks, dunnage or chocks properly secured to the load bed, or additional lashing.
The guidance is equally firm about friction. A high-friction surface can be an effective part of a load securing system, but it must not be used by itself - friction alone cannot secure a load. Friction matting or a high-friction floor is recommended for some load types, and effective high-friction surfaces should have a coefficient of friction of at least 0.6, which reduces the number of lashings needed. Plant and wheeled equipment carried on flatbeds, lowloaders and curtainsiders may need wheel chocks or timbers in addition to lashings, secured to the load bed themselves - unless the vehicle has wheel recesses or an auto-chock system.
Curtain-sider security fails in the gaps - literal and procedural. The loading plan should start with the body: is it XL-rated, and can this load be made to fit it to the 30/30/8-centimetre geometry? If yes, fill the gaps and document the fit. If no, select the equipment to match the load: straps and nets for items up to 400kg, rated lashings for anything heavier, blocking to the headboard, chocks for anything on wheels. And the driver who takes the curtain closed on a marginal load owns the result - the curtain will hide a shifting load from view right up to the moment it goes through the side. Side loading made the curtainsider universal; only proper restraint keeps it safe.
The XL rating that makes positive fit possible is a property of the specific body, not of curtainsiders generally - and fleets should know which of their trailers carry it. Body ratings are documented by the manufacturer, and the rating can be compromised by repairs and modifications over a trailer’s life: a body that left the factory XL-rated twenty years and three panel repairs ago may not still perform to the standard. The practical routine: record the rating of each trailer, verify it on acquisition, and treat any structural repair as a prompt to re-check. Then match loads to trailers accordingly - genuinely positive-fit work to the XL bodies, restraint-by-equipment work anywhere else, and never an assumption that “curtainsider” and “XL” are the same word. The rating is the load security plan’s foundation; everything else is strapped on top of it.