Chapter 2: Proportion Passes & A / B / C Iteration

Created by Sarah Choi (prompt writer using ChatGPT)

Proportion Passes & A / B / C Iteration (30% Deltas)

From Brief to Package: The Vehicle Concept Pipeline

Proportion is the fastest lever you have for solving a vehicle design. Before surfacing details, decals, or paint, the silhouette and massing decide function, attitude, and brand. This article shows how to run disciplined proportion passes and structure A / B / C iterations using 30% deltas so ideas evolve quickly, stay readable, and hand off cleanly to production. The guidance is written equally for concept‑side artists who must explore options rapidly and production‑side artists who must package, fabricate, and ship.

1) Start at the brief, aim at the package

Every strong proportion pass begins with a sharp problem statement and a credible package target. Translate the brief into non‑negotiables such as occupant count, stance, track and wheelbase ranges, door count and opening type, powertrain layout, payload or hardpoint positions, turning radius, and clearance envelopes. Identify negotiables like canopy shape, overhang flavor, fender volume, and aero devices. Write these as a short paragraph you keep at the top of your canvas so each pass can be checked against reality. For production artists, clarify the hardpoints early—seat H‑point, eye‑ellipse, pedal box, suspension pick‑ups, weapon or sensor mount coordinates, battery or tank firewalls, and maintenance access—so proportion sketches converge toward something that can be built.

2) The proportion pass: shaping silhouette, stance, and volume budget

Treat the first pass as a choreography of big shapes. Work in flat value or two‑tone paint to avoid detail gravity. Establish stance by fixing ground plane, ride height, camber attitude, and front‑to‑rear rake. Decide the relationship between body cabin and power volume: cab‑forward, cab‑rearward, mid, or distributed. Allocate the volume budget as percentage blocks, for example forty percent cabin, thirty percent power, twenty percent cargo, ten percent aero and accessories, then push and pull until the silhouette tells a single sentence story. For wheeled vehicles, commit early to wheelbase, track, and overhang proportion as those lock in handling language. For aerospace and spacecraft, set fuselage fineness ratio, lifting‑body proportion, and propulsor diameter to body length ratio because these drive performance reads. For walking or hover platforms, define foot or thruster spacing and the stride triangle so balance looks credible.

As you iterate, pressure test packaging assumptions using simple rectangles and cylinders. Drop in standardized human figures for scale and check line‑of‑sight, egress, and reach. Place weapon arcs or sensor occlusion cones as transparent wedges to catch impossible angles. Keep three to five silhouettes on one page so comparisons remain honest and deltas are obvious.

3) What counts as a “30% delta” and why it works

A 30% delta means each variation changes roughly one third of the design’s decisive information while preserving the remaining two thirds of its DNA. The goal is to move far enough to discover new opportunities but not so far that feedback becomes taste‑based rather than problem‑based. In vehicles, decisive information clusters around massing proportion, stance, cabin‑to‑power ratio, wheelbase‑to‑height ratio, and signature lines. If you keep, for instance, the stance and wheelbase but change cabin fineness and overhangs, that is a legitimate 30% shift. Likewise, retaining aero spines and canopy geometry while flipping power placement from rear to mid can be a 30–40% step that still allows A / B comparisons.

To self‑check the percentage, list ten binary or scalar attributes that define the current design—wheelbase, overhangs, roofline, shoulder volume, body side sweep, greenhouse ratio, power unit placement, intake/exhaust language, aero device presence, and ground clearance. Change three substantially, adjust two lightly, and keep five untouched. This heuristic keeps you near the 30% rule without measuring pixels.

4) Structuring A / B / C sets for decision clarity

Use A as the “anchor,” B as the “strategic pivot,” and C as the “wild but feasible” exploration. A should honor every non‑negotiable and present the most conservative massing that still feels purposeful. B deliberately trades one or two negotiables to test a different reading—perhaps a shorter rear overhang with a more forward cabin or a raised beltline that improves armor reads. C should stretch the silhouette language to the edge of the brief’s tolerance, such as exaggerating track width for planted aggression, exploring tandem seating to tighten fuselage cross‑section, or inverting the canopy‑to‑body ratio for a reconnaissance role. Keep all three builds aligned with the same horizon and perspective, identical scale bars, and a shared value key so reviewers focus on deltas, not presentation differences.

Each set should arrive with a single paragraph describing the intent of the shift and the risks carried. Mention what you preserved from the prior design and why. If you are production‑side, add a sentence on packaging consequences such as new cooling path lengths, changed maintenance clearance, or altered center of gravity. These small notes prime stakeholders to give actionable feedback instead of taste notes.

5) Iteration cadence: Ideation → iteration → finals → handoff

During Ideation, your goal is breadth. Generate three A / B / C trios that explore distinct proportion territories, not three permutations of one idea. For example, one trio might be cab‑forward utility, another long‑hood performance, and a third monococque pod with integrated aero. In each trio, keep forms blocky, spend detail on the read that proves the concept, and annotate the page with tiny packaging doodles that prove feasibility. At this stage, discard freely; you are buying information, not polishing assets.

During Iteration, your goal is depth. Select one promising territory and run stacked 30% deltas along specific axes: stance sweep, greenhouse proportion, power layout, or payload integration. Work in side, three‑quarter, and plan views to squeeze ambiguity out of the massing. Invite constraints. Ask production artists for a provisional hardpoint sketch. If a system requires a minimum duct cross‑section or recoil clearance path, draw it as a transparent overlay and let it slice your volume. The best 30% deltas often come from accepting a constraint and turning it into a signature.

During Finals, your goal is proof. Lock one proportion and run a tightening pass on surfacing intent and part breaks. Clarify panel strategy, hatch swing arcs, hinge volumes, and service joints. If the design carries decals, insignia, or numbering, reserve flat fields where production livery can live without being tortured by compound curvature. Freeze the wheelbase or equivalent governing dimension and note it clearly on the sheet. Make a simple materials intention sheet—metal, composite, fabric, glass—at the read level, not the shader level.

During Handoff, your goal is continuity. Export clean orthographic views with scale bars and dimensions for wheelbase, track, overall height, and key clearances. Provide a plan view, at least one section cut through the cabin, and a simple exploded diagram for layered assemblies. Include a callout page that points to interfaces, maintenance access points, weapon or sensor hardpoints, and any articulation paths. Add a final note capturing what was not solved and what is intentionally left to production design so expectations are clear.

6) Measuring and visualizing deltas for honest comparisons

To keep 30% deltas honest, use overlays and heatmaps. Duplicate the previous pass, set it to low opacity, and draw the new pass over it so moves are explicit. Create a “delta mask” layer where you paint changed regions in a single flat tone. If the changed area covers about a third of the silhouette’s area or affects three of the ten decisive attributes, you are in the zone. Keep a small ruler and protractor graphic on your sheet; mark the wheelbase and a couple of key angles like roof rake and nose dive. These simple marks make deltas measurable across the set.

Production artists can add quick proxy checks: place mass proxy blocks for engine, battery, or fuel and estimate center of gravity; simulate a turning sweep to ensure front fender volumes clear during full lock; sketch recoil vectors and travel for turrets so muzzle blast does not cook sensors; place a dummy service cart and technician to proof maintenance reach. These do not need to be CAD‑precise; they simply keep the proportion work honest.

7) Reading and managing risk

A / B / C sets are also risk maps. Label risks as feasibility, pipeline, or brand. Feasibility risks include complex glazing or illegal wheel coverage. Pipeline risks include forms that are hard to unwrap or rig. Brand risks include breaking signature lines that marketing counts on. Place a short “risk ledger” paragraph below each card that acknowledges these. The act of labeling allows stakeholders to opt into risk knowingly and prevents late‑stage surprises. When a delta carries significant feasibility risk, pair it with a mitigation note such as moving a hinge line, splitting a large panel, or accepting a small mass penalty for a clearer read.

8) Working across vehicle families and variants

Proportion passes scale well when designing trims and variants. Start with a core massing that encodes the brand sentence, then generate trims with constrained 30% deltas that swap capability reads without erasing identity. A base cargo trim might extend wheelbase slightly and raise roofline for cubic capacity. A reconnaissance trim might slim the greenhouse, move the cabin rearward, and carve body side scoops to signal speed and sensor cooling. A heavy assault trim might widen track, deepen shoulder volumes, and add underslung armor skirts. By holding one or two signature references constant—such as the headlight eyebrow or the shoulder break—you can produce a family that reads as cousins, not strangers.

9) Communicating with livery, insignia, and numbering in proportion passes

Even in early passes, reserve zones where faction identity can live. Mark flat, low‑warpage panels for insignia and high‑visibility surfaces for numbering. Keep the typography rectangles legible at game camera distances. In A / B / C sets, avoid moving these zones so downstream livery exploration remains interchangeable. When a 30% delta shifts a panel edge and jeopardizes insignia placement, note it in the margin so the branding pipeline can respond.

10) File hygiene, naming, and review rhythm

Clear labeling makes iteration feel safe. Name sheets with project, vehicle code, set, and date, and place the same label in a corner of the canvas. Keep the three views in consistent positions between passes. Use neutral lighting and a shared value key. Annotate with short, declarative sentences. For review rhythm, show three trios maximum per meeting to guard attention and make decisions. End each review by choosing a single trio to continue, or a single territory to deepen, and write the next delta axis as a one‑line brief at the bottom of the chosen sheet.

11) Common failure modes and how to avoid them

Designs fail when you polish too early, jump deltas so wide that intent is lost, or hide risk behind beautiful paint. Prevent this by staying in value, tracking decisive attributes, and labeling risks. Another failure is to ignore packaging until late; the fix is to invite constraints early and let them become signatures. Finally, teams sometimes fall in love with a one‑off hero shape that cannot scale to trims; cure this by proving at least one trim within the iteration phase before calling finals.

12) A compact case study: light recon rover

Suppose the brief calls for a two‑seat light recon rover for urban canyons with high sensor coverage and quick dash capability. The anchor A sets a short hood, mid cabin, and neutral overhangs for maneuverability. B pushes cab‑forward to maximize visibility and shortens rear overhang to improve breakover, accepting a taller greenhouse that increases drag. C shifts to a rear‑biased cabin with a long hood for a predatory read and hides sensors under a continuous brow, trading some near‑field visibility for intimidation. After review, the team chooses B and runs depth deltas: one reduces roof height by fifty millimeters while adding a periscope sensor; another widens track by seventy millimeters for planted stance; a third rotates the cabin five degrees forward for urgency. Packaging overlays reveal that the periscope frees up hood height for a larger radiator, which becomes a brandable grill. Final handoff includes orthos with wheelbase and track, a plan view with canopy hinge sweep, a section through the instrument cluster showing sensor cable routing, and a callout for quick‑release fender panels to service wheel hub motors.

13) Production‑side tightening without losing soul

As production artists take ownership, gesture and proportion must be translated into believable part breaks and fabrication logic. Keep hero curves as splines that can be approximated with manufacturable arcs and chamfers. Maintain the spirit of the stance by locking wheelbase and ground clearance before surfacing. Where concept left value masses, production should propose two or three plausible part break strategies and choose one that upholds the proportion story while reducing assembly count. Use shading IDs or flat material cards to maintain read while moving to buildable sections. When design debt appears—like a door that cuts into a structural arch—loop back with a targeted 30% delta that shifts the arch or door seam rather than shaving millimeters and losing clarity.

14) Hand‑off checklist

Before handing off, confirm that the final proportion sheet matches the last approved trio’s intent. Check that wheelbase, track, overall height, and overhangs are dimensioned. Ensure there is at least one plan view and a section cut for ergonomic truth. Include a short problem statement, the risk ledger, and an open items note. Provide a simple livery zone map. Attach delta overlays for the last two major shifts so downstream artists understand why the shape is the way it is.

15) Closing thoughts

Proportion passes are the art of declaring what matters early. A / B / C iteration with 30% deltas is the discipline that keeps exploration honest and feedback sharp. When both are practiced inside a pipeline that respects the journey from brief to package, vehicle design becomes a series of clear conversations rather than a tug of war. Concept artists get to explore boldly without breaking reality, and production artists receive shapes that already speak the language of build, service, and brand. The result is a vehicle that reads in a single glance, works in the hands of players and builders, and scales gracefully across a family of trims.