4-Link Suspension Calculator

Front & rear solid-axle worksheet — anti-squat, anti-dive, roll center, roll axis, pinion, caster & bump steer

Vehicle — roll axis & balance (front + rear together)

3D view — whole truck, drag to orbit, scroll to zoom

lower links upper links track bar / drag link instant center roll center / axis

Side view — both axles, roll axis & CG

Active axle schematics — drag the white pickup points

Active axle — geometry vs wheel travel

How the suspension worksheet works

Edit the rear 4-link and the front solid axle on one worksheet and see them together — the combined roll axis (front roll center to rear roll center), the front/rear balance, and how a swaying trailer is resisted.

Rear axle

  • Anti-squat % — from the side-view instant center: AS% = (IC height / IC distance ahead of the rear axle) ÷ (CG height / wheelbase). Resists rear squat under power.
  • Anti-lift % — the same geometry scaled by rear brake bias; resists rear-end rise under braking.
  • Roll center — panhard height at centerline, or the convergence height of triangulated links.
  • Pinion-angle sweep — pinion rotation across full travel (a planar 4-bar solve). Lower is better.
  • Roll steer — first-order tendency from the lower-link angle (understeer vs oversteer).

Front axle

  • Anti-dive % — the braking analog of anti-squat, from the front IC and front brake bias.
  • Caster & caster change — static caster plus how much it swings through travel (locked to the pinion on a solid axle).
  • Bump steer — toe change through travel from the track bar vs drag-link arc mismatch.
  • Front roll center — track bar height at centerline.

Vehicle

  • Roll axis — the line from the front roll center to the rear roll center, and its inclination.
  • Balance & roll moment arm — front/rear weight split and CG height above the roll axis.

Rear target bands (tow + moderate offroad)

  • Anti-squat — ~60–65% unloaded (rises to ~65–80% loaded after air-ride leveling); ceiling ~85%.
  • Anti-lift — ~20–45%, falls out of the anti-squat geometry.
  • Roll center — ~18–24" (near axle-tube height).
  • Pinion sweep — under ~5–6°; run a double-cardan driveshaft.

Front target bands

  • Anti-dive — ~20–30%; over ~40% rides harsh while braking.
  • Caster change — under ~3° over full travel (long links keep it small).
  • Front roll center — ~16–18", at/just below axle height and slightly below the rear RC.
  • Bump steer — under ~0.5° total; match the drag link to the track bar.

Vehicle target

  • Roll axis — nearly level, rear RC a touch higher (~1–2° nose-down). Get understeer from the front roll-stiffness bias, not by jacking the rear roll center.

Target bands are starting points to verify on your truck — CG height in particular is an estimate and strongly affects anti-squat.