A loading dock has one floor height. The trucks that come to it have several. When the two do not match, the cost shows up as slow loading, goods carried by hand, damaged pallets and a driver who is sent to another bay.
This article shows how to measure the gap, how to choose equipment that covers it, and what to tell your transportation company so the right truck arrives.
Two kinds of bay, and what each one needs
The textbook describes two basic designs.
- Level intake. The warehouse floor is at the level of the road. A forklift unloads the truck from the side. No height match is needed, because the forklift reaches up to the bed.
- Raised dock. The warehouse floor is at the height of a truck bed. A pallet truck or forklift drives straight onto the truck from the back. This is the normal design for box bodies and containers, and it is faster.
Most sites need both. A raised dock is only as good as its match to the trucks that use it. That match is the subject of this article.
The gap is a slope
A dock leveller is a steel plate that bridges the dock and the truck bed. It slopes up or down to meet whatever height the truck has. The textbook says the leveller must be long enough to cover all the vehicles you expect on that bay.
The slope is simple arithmetic: the height difference divided by the length of the plate. A bigger difference or a shorter plate gives a steeper slope. A steeper slope is harder for a loaded pallet truck to push up, and harder to hold when going down.
An illustration, with made-up heights, not measurements of any real fleet or dock:
- Dock floor: 1.20 m above the yard
- Leveller length: 2.0 m
| Truck | Bed height, loaded | Difference from dock | Slope on a 2.0 m plate |
|---|---|---|---|
| Four-wheel box | 0.85 m | 35 cm below | 17.5% |
| Six-wheel box | 1.10 m | 10 cm below | 5.0% |
| Ten-wheel box | 1.25 m | 5 cm above | 2.5% |
| Trailer | 1.40 m | 20 cm above | 10.0% |
Read the table the way the manager of that dock would. Three of the four trucks are workable. The small truck is not: a steep plate means slow, careful pushing, or loading by hand. One truck type quietly sets the speed of the whole bay.
The textbook gives a slope figure only for a driveway down to a raised dock: less than 10 per cent, with the vehicle level at the bay. No Thai standard for the slope of a dock leveller was found, so the working limit for your site is the maximum slope stated in your leveller supplier's specification for the equipment you run.
Measure, do not assume
Do not take bed height from a vehicle class name. Two six-wheel trucks can sit at different heights. Measure.
- Stand a truck on the level yard and measure the bed to the ground. Do it for every body type that visits your dock, not just your regular carrier's.
- Measure it empty and loaded. A truck rides lower on its springs when full and rises as it is unloaded, so the gap changes during the job. This is general vehicle behaviour, not a Thai figure, which is why your own measurement matters.
- Write down the lowest and highest bed you see. Your leveller has to cover that range, not the average.
- Record tailgate or tail lift if fitted. A body with a lift is loaded differently from one without.
Ten trucks measured over one week is a better guide than any catalogue.
Three limits that are easy to miss
- Height. Thai law caps a goods vehicle at 4.00 m overall, measured from level ground to its highest point, not counting mirrors. A canopy, door or shelter lower than that can stop a legal truck from entering. Check your lowest clearance against 4.00 m, and against what actually arrives.
- Width. The same regulation sets the width cap that decides what fits a bay between its bumpers and wheel guides. See how the legal width limit decides pallet fit.
- A depressed driveway. If you cut a ramp down to a raised dock, the textbook wants a gentle slope below 10 per cent and the truck on the level at the bay. A truck that is still tilted at the door makes the gap larger and the load less stable.
What goes wrong when the bay and the truck do not match
- Loading slows down. A steep plate, a missing plate or a gap to bridge by hand adds minutes to every pallet. At volume this is the queue described in why trucks wait at your loading dock.
- Damage rises. A pallet that drops, tilts or is dragged over a gap takes damage that the carrier will later dispute.
- The wrong bay gets used. Drivers are moved around, and the one low truck holds up everyone behind it.
The fix is rarely a new building. It is usually one of: a longer or a wider-range leveller on one bay, one bay set aside for low trucks, or a rule about which truck type is booked to which bay.
Tell the carrier, in writing
Your transportation company can only send a truck that suits the bay if it knows what the bay needs. This belongs in the booking, along with the other facts in what a carrier needs to quote. Put these on one page:
- Loading method at each bay: raised dock with leveller, or level intake with forklift from the side
- Range of bed heights the bay can take, from your own measurements
- Lowest overhead clearance on the way in, and the bay door height
- Whether a lift or ramp is available, and for which bays
- Body types you cannot take at this site
The same fact matters when you choose the truck size: a smaller truck may cost less per trip and cost more at the dock.
Where the evidence stops
No Thai study of dock heights, and no published Thai figures for load-bed heights by truck type, were found. Thai law sets an overall height limit but no limit on bed height. The method comes from the textbook, the 4.00 m limit comes from Ministerial Regulation No. 60 read in Thai, and every height and slope in this article is an illustration. Your own tape measure is the real data.
What to do on Monday
- Measure the dock floor height at every bay, and the lowest clearance on the way in.
- Measure the bed height, empty and loaded, of ten trucks that visit, and note the body type.
- Work out the slope for each: height difference divided by leveller length.
- Compare the worst slope with your leveller supplier's stated limit.
- Decide which bay takes the low trucks, and write the bed-height range on the access sheet you send to carriers.