No. 12
What role does bread tray weight play in determining dolly load limits and in-store maneuverability?
- 5 sections
- 1 table
Tray weight is a fixed charge on every dolly load: the number of trays times the empty weight of each tray. In the worked example below it is a smaller share of the load than the product, and a smaller lever on push force than stack height or a ramp. It matters most in two places: when a dolly is close to its rated capacity, and when a route includes a ramp where every pound of gross weight turns into push force. The useful way to set a dolly load limit is to start from the force a driver should push, then work back to trays per dolly, with tray weight as one term.
The gross load equation
Gross dolly load = dolly weight + trays per dolly x (empty tray weight + product per tray)
For example, imagine SPF Plastic Group’s published figures (SPF 2226 dolly, 12.8 lb; SPF 650 tray, 4.10 lb) with 12 lb of bagged product per tray, a figure you would replace with your own pack-out:
| Trays per dolly | Gross load | Tray weight in that load |
|---|---|---|
| 6 | 109.4 lb (49.6 kg) | 24.6 lb |
| 8 | 141.6 lb (64.2 kg) | 32.8 lb |
| 10 | 173.8 lb (78.8 kg) | 41.0 lb |
Two observations come straight from the table. Adding two trays adds 32.2 lb, far more than any realistic change in tray design would remove. And a tray that weighs 1.0 lb less takes 8 lb off an eight-high column, about 6 percent of the gross load. That is worth having, but it changes how many trays fit on a dolly only when the dolly is already at its rating.
The dolly’s rated capacity is a separate number the supplier should state in writing. SPF’s spec sheet for the 2226 lists dimensions, weight and truckload quantity but no load rating, so ask for the rating and for the caster rating behind it.
Push force is the limit that binds in the store
A driver feels gross load as push force, and push force has three parts: getting the dolly moving, keeping it moving, and climbing slopes.
Slopes. On an incline, gravity adds a share of the gross weight equal to the sine of the slope angle. The ADA Standards limit ramp runs on accessible routes to “a running slope not steeper than 1:12” (2010 ADA Standards, chapter 4). At 1:12 the gravity term is about 8.3 percent of gross weight:
- 6 trays: 9.1 lbf
- 8 trays: 11.8 lbf
- 10 trays: 14.4 lbf
Receiving ramps outside accessible routes can be steeper than 1:12, so measure the slope at each store that has one.
Rolling and starting. Starting force and the force to keep the dolly rolling depend on casters, floor, thresholds and maintenance more than on the tray. They have to be measured, not calculated: a force gauge on the dolly handle, pushed the way drivers push it, on the floors and thresholds of real stores. Measure on level floor and add the slope term for ramps, or measure on the ramp itself and leave the slope term out; doing both counts the slope twice.
What to compare the measurements with. The U.K. Health and Safety Executive’s guidance on assessing pushing and pulling lists guideline figures of 20 kg (men) and 15 kg (women) for starting or stopping a load and 10 kg and 7 kg for keeping it in motion, and states that the figures “should not be regarded as weight limits or approved figures for safe pushing and pulling operations.” Treat any push-force number in a specification the same way: as a design target from a named source, not a legal ceiling. Before calling a figure a limit, ask your safety lead which rule it comes from.
On a 1:12 ramp, the gravity term alone for an eight-tray column is about 5.3 kgf, before rolling resistance. Compare that with the 7 kg guideline figure for keeping a load moving and the margin left for a sticky caster or a threshold is small. A lighter tray reduces the gravity term by about 0.66 lbf on that ramp for an eight-high column; removing one tray reduces it by about 1.3 lbf.
Maneuverability: where weight meets geometry
In a store, control matters as much as force. Three things change how a loaded dolly handles:
- Mass. More mass takes more force to start, stop and turn, and more distance to stop. That is where tray weight enters, in proportion to its share of the gross load.
- Height. A taller column moves the center of gravity up, so the same turn is more likely to tip it; the same arithmetic applies in the truck, covered in our guide to keeping loaded trays from shifting in transit. Stack height is set by product and reach as well; see our guide to dolly labor time and stack height.
- Clearances. The ADA Standards require door openings on accessible routes to provide “a clear width of 32 inches (815 mm) minimum” and walking surfaces “36 inches (915 mm) minimum.” A 22.6-inch-wide dolly such as the SPF 2226 passes a 32-inch opening with about 4.7 inches each side; a wider dolly, such as the SPF 2629 at 26.6 x 29.6 inches, should go through doors narrow side first. Back-of-house corridors and stockrooms may not be on an accessible route, so measure them.
Casters: match them to the gross load
The caster rating has to cover the gross load with margin, including the heaviest tray in the fleet and the heaviest product mix. A conservative working rule is to divide the gross load by three rather than four casters, because on an uneven floor one caster can carry little or nothing; this is a planning assumption, not a standard. Ask the dolly supplier for the caster’s rated load and wheel material, and choose the wheel for the floors the dolly sees most: hard warehouse concrete and store vinyl behave differently, and so do thresholds.
Setting a dolly load limit, step by step
- Measure the route. Steepest ramp slope, worst threshold, narrowest door and corridor on the path from truck to shelf at each store type.
- Measure forces. With a force gauge, record starting and rolling force for a loaded test dolly on those surfaces.
- Pick a design target. Choose the push-force target your safety lead accepts, with its source written next to it.
- Solve for trays per dolly. Use the gross load equation with your real tray and product weights, and add the slope term for stores with ramps unless the force was measured on the ramp itself.
- Check capacity. Confirm the result is within the dolly’s and casters’ written ratings.
- Check height. Confirm the top tray stays within the reach limit for lifting.
- Then compare trays. Run steps 4 and 5 with each candidate tray weight. If the lighter tray adds a tray per dolly at the binding store, it pays on every trip; if it does not, its value is in the lifting work instead, covered in our guide to tray weight and cumulative fatigue.
Set the limit by the worst store on the route, then let tray weight compete with stack height and caster choice for the margin that remains.