The strap over your load is not holding it
The label says LC 2,500 daN. Thrown over a load on a plywood deck, that strap contributes about 315 daN of restraint — one eighth of the number printed on it. Nothing is faulty and nothing is mislabelled. The label is answering a different question from the one being asked.
Two ways to use a strap, and only one of them uses the big number
Put a strap over the top of a load, anchor both ends to the rails, and crank the ratchet. Nothing about that arrangement stops the load sliding forward. The strap runs across the top, roughly at right angles to the direction the load wants to go. It is not in the way of anything.
What it does is press the load into the deck. That extra downforce increases friction, and friction is what stops the load. This is a top-over or friction lashing, and it works entirely at second hand.
The other way is a direct lashing: the strap runs from an anchor point to a lashing point on the load itself, at an angle, so it is genuinely in the load's way and takes the force in tension. Only then does the strap's rated strength come into it.
| Direct lashing | Top-over lashing | |
|---|---|---|
| What resists the load | The strap, in tension | Friction on the deck |
| Figure that governs | LC — lashing capacity | STF — standard tension force |
| Typical on a 50 mm strap | 2,500 daN | 350 daN |
| Friction matters? | Helps | Decides everything |
Both numbers are on the label of every EN 12195-2 strap, along with SHF — the standard hand force, 50 daN, being the pull on the handle that the STF assumes. Nearly everybody reads LC and stops. In a top-over lashing the strap never goes anywhere near LC, and it is not supposed to.
What the load is actually trying to do
EN 12195-1:2010 does not ask you to hold the load's weight. It asks you to hold a fraction of it in each direction, and the fractions come from how hard a truck can brake and corner:
| Direction | Required | Comes from |
|---|---|---|
| Forward | 0.8 g | Emergency braking |
| Sideways | 0.5 g | Cornering (0.6 g if the load is unstable) |
| Rearward | 0.5 g | Acceleration |
So a 2,000 kg crate has to be held against 0.8 × 2,000 × 9.81 = 15,696 N trying to send it through the headboard. That is the target.
Where most of that force is already handled — for free
The load is sitting on the deck under its own weight, and that already generates friction. The only shortfall you have to make up with straps is what friction does not already cover. Each top-over lashing closes part of that gap: it presses down with its pretension on both legs, and only the friction that downforce generates counts.
That is the whole of EN 12195-1:2010's top-over equation, rearranged to give the number of lashings:
m × g × (cx,y − μ × cz) × fs
n = ─────────────────────────────
2 × μ × FT × sin α
| Symbol | What it is | Value |
|---|---|---|
| cx,y | Horizontal acceleration coefficient | 0.8 forward · 0.5 sideways and rearward |
| cz | Vertical coefficient | 1.0 |
| fs | Safety factor | 1.25 forward · 1.1 sideways and rearward |
| μ | Friction factor for the two surfaces | From Annex B — see below |
| FT | Strap pretension: the STF, not the LC | 350 daN typical |
| α | Angle between lashing and platform | 90° is vertical |
| 2 | Because a top-over lashing presses with both legs | |
Notice what appears twice: μ. It sets how much restraint you already have, and it sets how much each strap is worth. That is why friction is not one factor among several here. It is the factor.
The IRU load securing guidelines publish a worked example: two lashings, μ 0.45, STF 400 daN, α 55°, giving 1.4 t forward and 10.9 t sideways. The equation above returns 1.37 and 10.93. It reproduces the published figures, which is why it is on this page.
The same crate, three decks
2,000 kg, held forward at 0.8 g, with 50 mm straps at STF 350 daN thrown vertically over the top. Only the surface underneath changes.
| What it sits on | μ | n | Straps |
|---|---|---|---|
| Plastic pallet on plywood | 0.20 | 10.51 | 11 |
| Steel crate on plywood | 0.45 | 2.73 | 3 |
| On an anti-slip mat | 0.60 | 1.17 | 2 |
Eleven straps over one pallet. Nobody does that, which is the point: the load in the top row is not secured, and the delivery note does not know. The bottom row is the same crate, the same truck, the same straps — with a rubber mat under it.
An anti-slip mat costs a few euros and takes this load from eleven straps to two. It does more for a low-friction load than any number of straps you could physically fit over it, and it is the most under-used piece of equipment in road freight.
The angle, which is quietly halving your work
sin α in that expression is the angle of the strap to the deck. Vertical is
sin 90° = 1 and you get everything. A strap leaning over at 30° gives
sin 30° = 0.5 — half the downforce, so twice the straps. The 0.45 case above goes
from three straps to six for no other reason.
Straps thrown over a wide load and anchored close in end up shallow without anyone deciding that. It is worth looking at the angle before deciding you have enough.
Back to the label
Now the opening figure. One strap, vertical, on the plywood deck at μ 0.45:
0.45 × 2 × 350 daN = 315 daN of restraint
The label says 2,500. The strap delivers 315 — about 13 % — and it is working exactly as designed. LC 2,500 daN is what the strap can take in a direct lashing before it fails. It has nothing to do with how much friction a ratchet's worth of pretension buys you.
Anyone counting straps against the weight of the load using the LC figure is out by roughly a factor of eight, in the unsafe direction.
What this page does not do
This is the mechanics, not the method. EN 12195-1:2010 is the document you work from, and it is stricter than the bare physics above in ways that matter:
- Sliding is only one failure. A tall load tips before it slides, and that is a separate calculation this page has not touched.
- Friction is not a securing method on its own. Where μ already exceeds the required coefficient the arithmetic says zero straps, and that is not an answer. Vibration walks a load along a deck over hours in a way a static friction figure does not describe.
- Blocking against the headboard, filling voids and using the vehicle's own structure are often better than lashing at all, and are outside this page.
- Friction factors depend on both surfaces being clean and dry. Oil, ice, dust and a worn deck all take μ below the table value, and nothing on the paperwork records that.
Equation, acceleration coefficients, safety factors and friction factors from EN 12195-1:2010, as reproduced in the IRU International Guidelines on Safe Load Securing for Road Transport; label definitions from EN 12195-2. Strap figures are a common commercial specification (50 mm webbing, LC 2,500 daN, STF 350 daN), not a universal one — read your own labels.
What to take away
- Read STF, not LC, whenever the strap goes over the top.
- Look at what the load is standing on before you count straps. It changes the answer more than anything else you can do.
- Carry anti-slip mats. They are cheaper than the straps they replace and far cheaper than the load.
- Get the straps steep. A shallow angle silently doubles what you need.
- Work from the standard for anything you are signing for, and get the training if it is your job. This page explains why the numbers behave as they do; it does not replace them.
And before any of it: know where the weight is sitting. The axle weight calculator covers what the load does to the vehicle, and the mixed load calculator covers what a set of different pieces does to each other.