Axle-Load Tandem Slide
Over/under per axle group, weight shift per slider hole (lever-arm), holes to slide and direction.
Example
You enter
- Drive-tandem weight (lb) 35200
- Trailer-tandem weight (lb) 32000
- Kingpin-to-tandem distance (in) 400
- Hole spacing (in) 6
- Legal tandem cap (lb) 34000
You get
- Weight shift per hole 480 lb/hole
- Holes 3
Details, formula, and sources
Over/under per axle group, weight shift per slider hole (lever-arm), holes to slide and direction, and projected drive/trailer weights to bring a tandem under the legal cap.
Lever-arm: moving the tandem d inches changes the trailer reaction by dW = trailer_load * d / L (L = kingpin-to-tandem). shift_per_hole = trailer * hole_spacing / L; holes = ceil(target_shift / shift_per_hole).
Per the federal axle/gross weight limits - 23 CFR 658.17 (12,000 lb steer, 34,000 lb tandem, 80,000 lb gross) and the federal Bridge Formula, by name; lever-arm statics is public.
Free at ecfr.gov; cross-references the bridge-formula tile. FMCSA enforces.
Estimate. AHJ and licensed professional govern.
Field names used by the API: drive_lb, trailer_lb, kingpin_to_tandem_in, hole_spacing_in, tandem_cap, shift_per_hole_lb, holes
- Per-hole shift computed from the lever arm (trailer load * spacing / kingpin-to-tandem distance), not assumedstatics