Sarah Clarity Studios

Chapter 1: Track Geometry & Suspensions

Created by Sarah Choi (prompt writer using ChatGPT)

Track Geometry & Suspensions for Vehicle Concept Artists — Land Vehicles: Tracked & Articulated

Tracked and articulated vehicles exchange tire contact patches for belts of links or hinged frames that spread load, cross obstacles, and pivot in place. They are the backbone of combat, utility, and construction fleets where ground pressure, traction, and approach angles matter more than top‑speed refinement. For vehicle concept artists on both the concepting and production sides—across indie and AAA—understanding track geometry and suspension families lets you design silhouettes that read terrain truth and hand off packages that rig and simulate cleanly.

Why tracks and articulation

Tracks reduce ground pressure by enlarging the contact area and maintain traction on soft, uneven, or debris‑covered surfaces. Articulated frames (think articulated dump trucks or loaders) split the vehicle into front and rear halves connected by a joint, preserving tire simplicity while enabling tight turning and terrain following. Combat platforms choose tracks for trench crossing, step climbing, and pivot‑turning; construction chooses tracks for grading and pushing; utility (snowcats, pipeline carriers) chooses tracks for low ground pressure on snow and muskeg. Your silhouette should make that purpose obvious before any texture loads.

Track geometry: the belt you must draw honestly

A track loop is defined by sprocket(s), idler(s), road wheels/bogies, and return path/rollers. The geometry creates the silhouette cues players trust.

Pitch and link type. Track pitch (distance between pin centers) and whether links are single‑ or double‑pin set the visual cadence. Combat tracks often show robust double‑pin, center‑guide links; construction and utility may use rubber belts with molded guides. Keep lug rhythm consistent; moiré happens when link cadence doesn’t scale to camera distance.

Contact length and ground pressure. The lower run between the foremost and rearmost road wheel contact defines contact length. Long contact length + wide shoes = low ground pressure and excellent flotation; shorter length + narrow shoes favors agility and turning ease. Express flotation with longer, flatter lower runs and broader shoe geometry; express agility with shorter, slightly arced lower runs.

Sprocket vs. idler position. Rear‑drive sprockets are common on MBTs; front‑drive on some IFVs and construction gear. Idlers typically sit opposite the drive. Their radii and positions set approach/departure and trench‑crossing ability; a higher leading idler with a forward‑reaching shoe projects good step climbing.

Return path and sag. Steel tracks often droop between return rollers; rubber belts ride on top rollers or a smooth slider. Controlled sag reads weight and tension. A totally straight upper run on a heavy combat vehicle looks wrong; a deep catenary on a rubber snowcat looks wrong. Design target sag and carry it through orthos and rig notes.

Guide horns and pads. Center guide horns engage road wheels; outer guides prevent de‑tracking on some systems. Bolt‑on rubber pads (road pads) appear on urban kits; grousers or ice cleats appear on winter or soft‑ground kits. Make pad width and bolt patterns believable; they drive decals and wear.

Shoe width and grouser form. Wider shoes and tall grousers signal soft‑ground specialization; shorter grousers and replaceable pads signal hard surfaces. On snowcats, chevron or ladder grousers on rubber belts are common.

Tensioners. Idler carriers and hydraulic cylinders set track tension. Indicate adjuster access and travel in callouts; it affects maintenance gameplay and rigging range.

Suspension families: how the hull meets the ground

The suspension under the skirts governs ride, firing stability, grading accuracy, and crew/driver fatigue. Different families telegraph era, cost, and capability.

Christie / large‑wheel coil spring. Few large road wheels, no return rollers, big idler/sprocket—classic early fast tanks. Silhouette shows big wheel daylight and minimal upper run support.

Torsion bar (combat staple). Multiple small/medium road wheels, low hull floor, compact packaging. Bars run across the hull with swing arms at each wheel station. External silhouettes show evenly spaced wheels; cutaways must show arm pivots and bar paths. Easy to show add‑on shock absorbers at select stations.

Horstmann / bogie units. Paired wheels on sprung bogies with external coil springs. Common on older and some modern AFVs; silhouette shows discrete bogie housings—great for readable rhythm and field maintenance flavor.

Hydropneumatic / adjustable. Road wheels on arms connected to struts that can vary ride height and attitude. Modern MBTs/IFVs and high‑mobility utility tracks use this to “kneel” or trim for firing. Indicate accumulator bulges, line routing, and service ports; provide pose range in callouts for rig/animation.

Roller‑frame (construction). Excavators and dozers use bogie frames that let the lower run conform to terrain for traction while providing a slider or rollers on the return. Silhouette shows more wheels and longer lower runs; cutaways must show carrier rollers and frame pivots.

Rubber‑belt suspensions (utility/snowcat). Tracked carriers and snowcats use lighter road wheels on torsion beams or simple bogies under a continuous rubber belt. Show belt thickness, molded guides, and side protection rails.

Articulated suspensions: hinge the world

Articulated dump trucks (ADTs), loaders, and graders split the frame and steer via a central articulation and oscillation joint. The joint permits yaw (steer) and roll (terrain follow). Silhouette cues: narrow waist, visible hydraulic steering cylinders, and oscillation pin. Provide joint range (± steer, ± roll) and hose routing in callouts; rigging relies on these limits.

Skid‑steer (compact loaders). Differential speed turns; tracks can be rubber over bogies or steel; silhouette is boxy with strong lift arms. Show roller packs and tensioners, plus track shoe wear plates.

Combat, utility, construction: translating purpose into form

Combat (MBTs, IFVs, SPGs).

• Mission tells: low, long hulls for MBTs; higher troop compartments with rear ramps for IFVs; rear casemate or open deck for SPGs.
• Mobility cues: wide shoes, robust grousers, side skirts with replaceable tiles, hydropneumatic pose panels for modern kits.
• Protection interfaces: ERA/NERA tiles, side skirt hangers, belly armor for blast protection; visible tow eyes and recovery points.
• Deliverables: trench‑crossing length, vertical step, fording depth, turn‑in‑place radius (0 for neutral steer), ride height bands (travel/combat/kneel), wheel station coordinates, recoil clearance envelopes.

Utility (snowcats, pipeline carriers, expedition platforms).

• Mission tells: large cargo decks, modular cabins, crane mounts, ultra‑low ground pressure.
• Mobility cues: very wide belts, low belt tension/sag, generous fender daylight with snow eject channels, sealed bearings.
• Deliverables: ground pressure targets (kPa), deck load limits, belt OD, belt guide geometry, heater/defroster intakes, service hatches for idlers/rollers.

Construction (dozers, excavators, compact track loaders).

• Mission tells: dozer blades with tilt/angle/pitch cylinders; excavator carbody with swing bearing and track frames; CTLs with vertical or radial lift arms.
• Mobility cues: long lower runs for push/pull, roller frames with oscillation, track guards, mud scrapers.
• Deliverables: blade or bucket working envelopes, swing clearance, undercarriage track frame dimensions, roller/idler service access, debris paths.

Packaging and service: what must fit and be reachable

Tracks are maintenance‑heavy. Show track pin access, pad bolt access, grease points, shock absorber locations, and adjuster ports. On combat vehicles, plan skirts as modular panels with fastener logic and lifting points; call out escape paths if skirts must be jettisoned. On construction gear, show carrier roller guards and clean‑out doors. On articulated machines, route hoses/cables through guarded passages with slack and rub strips for full joint travel.

Rigging & implementation notes: make motion cheap and true

• Track path. Provide a clean spline/mesh path for the track loop (lower run, sprocket wrap, idler wrap, upper run). Include target sag and the number of visible links.
• Link animation. Recommend a UV scroll for rubber belts; for steel links, a link‑by‑link rig or bones along a spline. Supply pivot coordinates for sprocket/idler and wheel station centers.
• Wheel station hierarchy. Name and place road wheel pivots (and arms where visible), carrier rollers, idler carrier, and tension cylinder. Provide travel ranges and pose states (transport/combat/kneel).
• Articulation joint. For ADTs/loaders, give yaw/roll limits and hose bundle constraints.
• Collision & FX. Provide contact boxes along the lower run for dust/snow/mud emitters; mark ejecta paths (mud scrapers, snow channels); provide spark zones for track slap or impact.

Camera reads: distance bands and weather

At far range, players must read: number of track units, skirt rhythm, and whether the vehicle can neutral steer (wide shoe + short body suggests in‑place pivot). At mid range, they should parse roller/bogie cadence, idler/sprocket positions, and skirt tile pattern. At near, they should see pad/grouser detail and wear on guide horns. Weather tests: dust halos on deserts, snow plumes that curl over fenders on snowcats, mud flings that track the lower run. Lighting should protect the silhouette by placing emissives at corner landmarks rather than along skirts where bloom kills detail.

Audio cues: sell mass and mechanism

Steel track clatter scales with speed on hard surfaces, dampens on soft; idler squeak and roller rumble at low speeds; hydraulic hiss and accumulator chirp on hydropneumatic pose; sprocket whine under load. Articulated machines add joint groan, tire thump, and frame creak. Pair clips in research packets with captions so mixing matches intent.

Concept → production deliverables

• Metrics & mobility sheet: Track pitch, shoe width, link count per side, sprocket/idler diameter, wheel station spacing, contact length, ground pressure target, trench/step/fording limits, neutral‑steer yes/no, articulation joint ranges.
• Orthos (measured): Side/front/rear/top with track path overlay (spline), wheel station coordinates, sprocket/idler centers, return rollers, skirt panels, fender and mud/snow ejection geometry.
• Cutaway: Suspension family (torsion bars, bogies, hydropneumatic), arm pivots, shock/strut placement, adjusters, tensioners, guides; for articulated: joint pins, cylinders, oscillation bearing, hose routing.
• Exploded views: Track link + pad + pin stack, road wheel assemblies, carrier rollers, idler carrier, sprocket segments, skirt tiles; for construction: roller frames and blade or arm subassemblies.
• Callouts: Track tension range, sag targets, pad bolt torque, roller diameters and materials, shock stroke, hydropneumatic pressure ranges, blade/boom working envelopes, articulation yaw/roll limits, hose minimum bend radii.
• Camera‑read boards: Far/mid/near, dry/dust, mud, snow; silhouettes with annotations of what must read at each band.
• Rig pack: Named hierarchy, pivots in project units, recommended bone counts, UV scroll speeds for belts, LOD gates for link frequency.

Indie vs. AAA cadence

Indie: combine silhouette, a measured side ortho with track path, a quick suspension cutaway, and a rig note block on one evolving canvas; validate with an in‑engine greybox and UV‑scroll belt quickly. AAA: separate gates—mobility metrics lock → suspension family lock → orthos/callouts for modeling kickoff → rig pack & FX pass → camera‑read sign‑off across biomes—plus a shared undercarriage kit (links, pads, rollers, skirts) to keep fleets coherent and performant.

Concept vs. production mindset

Concept protects purpose and terrain truth: choose track width, contact length, and suspension family to telegraph mission (assault, grading, snow). Production protects buildability and motion: encode track path, wheel station coordinates, tension ranges, and pose states so modeling, rigging, physics, VFX, and audio can act without guessing.

Closing

Tracks and articulated frames make vehicles look inevitable on hostile ground. When you draw the belt cadence honestly, choose the right suspension family, and package tensioners, rollers, and joints with service logic, your silhouettes read capability at a glance—and your handoff lets teams animate, simulate, and optimize without surprises. That is how combat tanks feel planted in a trench fight, how dozers push like gravity itself, and how snowcats glide across powder in your world.