Two costs, one number
Fit a paper roll clamp to a truck and the nameplate capacity is no longer the number that matters. The attachment takes its toll twice: first its own weight, hung ahead of the forks where the truck feels every kilogram; second the load it carries now sits further forward, because the attachment has thickness. Residual capacity is the manufacturer's statement of what the truck can still lift with the attachment fitted, at a stated load center — and it is always less than the nameplate by more than the attachment's own weight.
This is the mechanic our attachment buyer's guide flags as the first check before any order, and this article gives it a room of its own because it is the check most often skipped — and the one that turns a satisfied delivery into a truck that cannot lift the load it was bought for.
A worked example of the arithmetic
Take a truck rated 2,500 kg at 500 mm — the EP25's rating. Fit a hypothetical clamp weighing 350 kg with 100 mm of effective thickness: the attachment's weight subtracts directly, and the carried load's center of gravity moves outward by roughly the clamp's thickness, pulling the rating basis out to 600 mm and beyond for thick attachments. The residual figure the manufacturer publishes after both effects is the only capacity that exists on that truck. Clamps are the heavy case — the AT-PR351 paper roll clamp is a 3.5 t-class attachment — but the arithmetic is identical for a side shifter, which is why the EP30's standard side shifter is quoted with its residual figure rather than treated as free.
| Effect | Mechanism | Magnitude drivers |
|---|---|---|
| Attachment weight | Direct subtraction from capacity | Attachment mass — clamps weigh far more than shifters |
| Load-center shift | Load's center of gravity moves forward by attachment thickness | Attachment thickness and the load's own center |
| Hydraulic demand | Attachment functions share pump flow and pressure | Clamp/rotate functions; lift speed falls as functions add |
| Stability at height | Combined center of gravity rises and moves out | Worst at full mast height — read the chart, not the plate |
How to read a residual capacity statement
- Confirm the rating basis. Residual figures, like everything else, assume a load center — the 500 versus 600 mm question applies.
- Read it at your lift height. Residual capacity at the floor is a different number from residual at full mast; the load chart with the attachment's data governs.
- Check the hydraulic interaction. Powered attachments share the pump; confirm lift and travel performance with the attachment working, not just the static figure.
- Verify against the real load. Your heaviest roll, drum or bale at its true center against the residual figure — with margin, because the load behind the heaviest is the one that arrives unlabeled.
How we quote attachments
Every Granvolt attachment quotation — the AT-SS201 hydraulic side shifter with its ±100 mm side shift and ISO class II/III carriage, the AT-PR351 paper roll clamp with 360-degree continuous rotation — carries the residual capacity statement for the truck class it is destined for, with hoses and couplers included where the specification says so. If you are fitting a third-party attachment to a Granvolt truck, send its weight, thickness and function list with the RFQ and the engineering team will return the residual figures within 12 hours on average; it is a fifteen-minute calculation that we would always rather do before the purchase order than after the first disappointing shift.
Recording residual figures in the fleet file
Residual capacity is a document problem as much as an arithmetic one: the figure is only useful if it lives where the next decision happens. The working file keeps, per truck, its attachments with their residual statements, the load chart with the attachment data applied, and the date the figures were issued — because attachments move between trucks, and a residual figure that travels silently with the attachment becomes wrong the day it lands on a different truck class. Fleet auditors and safety inspectors ask exactly this question — "what may this truck lift with that clamp fitted?" — and the file answers in seconds what memory answers with risk. One folder per truck, updated when the attachment bolts go on, and the heaviest arithmetic in this guide becomes a lookup instead of a liability.
Frequently asked questions
What is residual capacity on a forklift?
The capacity that remains after an attachment is fitted — its weight subtracted and the load-center distance it adds accounted for. It is always below the nameplate figure by more than the attachment's own weight.
How much capacity does a side shifter lose?
Side shifters are the light case — the EP30 carries one as a standard option — but the loss is real and quoted in the residual figure rather than treated as zero.
Do powered attachments affect lifting speed?
They can: clamp and rotate functions share the hydraulic pump with lift, so lift speed falls while functions work. Check the hydraulic interaction with the attachment operating.
Does residual capacity change with lift height?
Yes — read the figure at the actual lift height from the load chart. The floor figure and the full-mast figure are different numbers.
Can I fit a non-Granvolt attachment to a Granvolt truck?
Send its weight, thickness and functions to our engineering team with the RFQ; we return the residual capacity figures for the truck class, typically within 12 hours.