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Sumner Lift Field Manual
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Field Manual  /  Capacity Calculator

Find the safe load for your actual setup.

Rated capacity assumes a centered, balanced load on un-extended forks, with outriggers deployed, on a level hard surface, indoors. Real conditions reduce that capacity. This calculator applies the engineering de-rates described in Sumner's operator's manuals to give you a defensible working number.

Educational reference, not engineering certification This calculator implements de-rate rules from Sumner's published operator's manuals and standard rigging-engineering practice. It is not a substitute for OEM guidance on your specific lift, and it does not replace a qualified rigger's judgment for non-routine lifts.
0 in
0°
50%
Adjusted Safe Working Load
650 lb
Rated 650 lb · 100%
✓ Within design margin
100%

Why this load was de-rated

Related

Methodology

How the de-rates are calculated.

FactorRangeEffect on capacitySource
Fork extension kit installed Yes / No Hard cap at 200 lb regardless of base capacity Sumner PN 783691 spec
Off-center load 0 – 18 in Linear fall-off, ~5.5% per inch Tipping-moment engineering rule of thumb
Floor slope 0 – 8° ~8% per degree of slope Sumner manual: hard, level surface only
Outriggers not deployed Boolean ×0.4 (60% reduction) Footprint-based stability calculation
Wind exposure None / Light / Strong ×1.0 / ×0.7 / ×0.4 Sumner manual: do not operate in wind
Mast extension 0 – 100% Up to 10% reduction at full extension Dynamic margin for slide-pad slop and sway
The de-rates are multiplicative Multiple factors compound. Off-center load on a slope with outriggers stowed isn't the sum of three penalties — it's the product. A 650 lb lift can drop below 100 lb safe working load very quickly when several factors stack.