2026 seasonIndependent racer resourceAkron, Ohio
SoapboxSpeed Lab

DRIVE / MEASURE / TEST

Ten things that decide the run.

Work the car in the order the measurements depend on each other, from the driver's line at the gate to the heat in the wheels, and leave with a record the team can repeat.

10 lessons in dependency order4 interactive toolsRules remain authority

CHOOSE A SETUP MISSION

What does the car need today?

Use the complete dependency path for a new baseline, a short recheck before race day, or a focused guide when one reading will not repeat.

START HERE

One rule sits above all ten lessons.

Ollie Brower stated it in Derby Tech in 1984 and nothing since has improved on it: "The racer that looses the least amount of energy will get to the finish line first." Two cars leave the same gate with the same energy. The winner is the one that wastes less of it, whether that loss goes into a steering correction, a bound wheel, a soft tyre, a crooked axle, or the air.

Every lesson below is one place that energy leaks. They are ordered so that each measurement is still true after the next one is taken; work them out of order and you will re-do them.

On when to do this work, the 1984 expert panel and readership agreed by 75% and 89% that new ideas get tested well in advance of race day. Gary McNall of Salem put the reason plainly: "You don't build your car at a race. You are there to race, so best be ready." Tony Carlini's answer to the same question was that his team usually started about 364 days out.

Legality boundary: the current ISBD or NDR rule book, division plan, amendment, inspection sheet, and race official control. Physics can explain a measurement, but it cannot authorize a body, axle, weight, wheel, fastener, lubricant, or material change.

TEN-LESSON PATH

Use a two-pass dependency order.

Lesson one is the driver, because the cheapest speed on any hill is a line that needed no correction. Lessons two through eight work the car in two passes: record the untouched car first, then set geometry, restore the clamp and cable state, and repeat the load measurements before any timed run. Nine and ten are the air and the heat, which are the last places to look and the smallest to gain. Revisit every affected upstream station after transport, a hard stop, a hardware change, or a reading that will not repeat.

  1. 01 / DRIVE THE LINEDriver routesOutside, inside, or straight. Set the angle at the gate, hold it, and practise hitting marks on a private hill.
  2. 02 / CAPTURE THE UNTOUCHED BASELINEBalance and corner loadRecord the original four-pad state before geometry or clamp work, then repeat it after step six.
  3. 03 / BUILD REFERENCESTriangulationCompare endpoint-defined diagonals while declaring centerline, contact, load, and tool direction.
  4. 04 / CHECK THE PLANECrossbindMeasure geometric lift separately from diagonal scale load and isolate fixture error first.
  5. 05 / AIM THE WHEELSSpindle alignmentRecord all four loaded spindle directions, sign conventions, and wheel/runout checks.
  6. 06 / RESTORE THE STACKKingpin torqueReturn the legal hardware, cable, and clamp stack to one documented state, then recheck steps two through five.
  7. 07 / VALIDATE MASS PLACEMENTTail weightReweigh the final assembly and compare legal ballast moves with measured process spread.
  8. 08 / LOCATE THE SYSTEMFore-aft center of gravityUse final axle loads and measured reaction spacing to locate the car-driver balance point.
  9. 09 / ACCOUNT FOR AIRAerodynamicsRelative airspeed, quadratic drag, legal presentation, and a drag curve.
  10. 10 / ACCOUNT FOR HEATThermal dynamicsSurface temperature, the boundary layer, warm wheels and axles, and the myths Derby Tech killed in 1984.

CAR-READY PREFLIGHT

Do not touch a setup tool until this record exists.

  1. Write sanctioning organization, division, car identity, plan revision, amendments, and the official who will resolve ambiguity.
  2. Photograph the fully dressed driver in the repeatable race position and confirm steering, braking, sight line, helmet clearance, and safe exit.
  3. Record wheel IDs and positions, ballast location and attachment, cable state, hardware stack, and the untouched four-pad loads.
  4. Identify each measuring tool, its resolution, zero or reference check, contact points, sign convention, and operator.
  5. Prove the bench, rails, or scale pads share the plane required by the measurement.
  6. Start a run log before you change anything, so the baseline, date, weather, lane, wheels, and result stay on one page together.

Start a run log in My Race Shop

MEASUREMENT DISCIPLINE

Repeatability comes before adjustment.

DEFINE

Name the measurand

Write exactly what is being measured, its units, reference points, load state, tool, resolution, and sign convention.

REPEAT

Break and remake the setup

Zero or tare, measure, remove and reset the tool or settle the car, then measure again. Repeated digits without a reset do not test the process.

DECIDE

Compare effect with noise

If a change is smaller than ordinary spread, report it as unresolved. Correlation is not proof of cause.

sample mean = Σxᵢ / n
range = maximum − minimum
sample standard deviation s = √[Σ(xᵢ − x̄)² / (n − 1)]

Calibration addresses relationship to a reference; repeatability addresses spread under the same stated conditions. Neither automatically includes fixture flex, operator changes, pad mismatch, temperature, transport, wheel variation, lane, wind, or driver posture.

INTERACTIVE BENCH

Calculate, then verify on the car.

These tools preserve units and assumptions in the open. Every prefilled number is an illustrative generic example, not a setup target, rule limit, or recommendation. Outputs are engineering aids, never inspection instructions.

GEOMETRY

Diagonal difference

Enter matched diagonal readings and your demonstrated repeatability band in one common unit.

Enter your own matched readings and a repeatability band demonstrated by complete tool resets. The worked example below is available without presenting it as your car's setting.

Equal diagonals establish square or center only if the reference points are actually symmetric and the intended centerline has already been validated.

STATIC EQUILIBRIUM

Four-scale and ballast map

Loads are pounds-force and distances are inches. Keep every pad coplanar and the driver untouched.

Enter the four raw scale readings, measured reaction spacing, and any permitted mass-move hypothesis. Keep the example numbers in the worked section separate from your team's record.
D = R − F
R = (W + D) / 2
xCG = R·L / W
Δ(R − F) = 2·w·Δx / L

A diagonal difference is a diagnostic, not proof of crossbind. Redistributing static load alone does not necessarily increase total rolling resistance.

RELATIVE AIR

Drag force and power

Use SI units. Relative airspeed is car velocity relative to the air, so headwind increases it and tailwind decreases it.

Enter one internally consistent SI test condition. Use relative airspeed for drag force and ground speed for the car's modeled mechanical-energy loss rate.
Fᴅ = ½ρCᴅAvrel²
Pvehicle = Fᴅvground
Drag force rises with the square of relative airspeed.

A/B TEST

Baseline versus change

Enter at least three comma-separated elapsed times in seconds for each condition. Lower is faster.

Enter at least three raw elapsed times for each randomized condition. Preserve run order, lane, wheels, weather, and rejected-run reasons in My Race Shop.

Randomize paired A/B order while holding wheels, lane, driver posture, load, release procedure, and conditions as constant as practical. A one-run gain is not evidence; an effect should exceed ordinary repeatability and survive replication.

WORKED EXAMPLES

Illustrative generic arithmetic, not setup targets.

Generic diagonal reading

Given: Dᴸ = 61.125 in and Dᴿ = 61.000 in.

Result: ΔD = 61.125 − 61.000 = +0.125 in. Compare that magnitude with repeated setup spread before deciding it belongs to the car.

Generic tail differential

Given: W = 200 lb and rear-minus-front D = 5 lb.

Result: R = (200 + 5)/2 = 102.5 lb and F = (200 − 5)/2 = 97.5 lb.

Generic fore-aft CG

Given: R = 102.5 lb, L = 84 in, W = 200 lb.

Result: x = 102.5 × 84 / 200 = 43.05 in behind the front axle.

Still-air drag example

Given: ρ = 1.20 kg/m³, Cd = 0.35, A = 0.45 m², vrel = vground = 15 m/s.

Result: Fd ≈ 21.3 N and vehicle loss rate Fd·vground ≈ 319 W.

A higher center of gravity does not automatically add usable energy. Available gravitational energy depends on the actual vertical drop of the combined center of gravity between start and finish along the real orientation and path.

SOURCES & FURTHER READING

Check the primary material.

  1. ISBD Rule Book - linked for the 2026 World Championship Official PDF currently linked from Race Week resources; the file itself says revised June 2025.
  2. ISBD race divisions and build plans Official division descriptions, age bands, weights, plans, and Legacy information.
  3. National Derby Rallies rules hub Official NDR landing page, 2025 tail-weight update, rule books, and inspection links.
  4. OpenStax University Physics: Conditions for static equilibrium University-level reference for force and moment balance used in axle-load and center-of-gravity calculations.
  5. OpenStax University Physics: Rolling motion University-level reference for translation, rotation, angular speed, and rolling without slipping.
  6. NIST Engineering Statistics Handbook: Uncertainties of calibrated values NIST guidance on uncertainty in future results corrected by a calibration curve, including calibration-curve and future-measurement contributions. It does not characterize the whole Derby measurement process by itself.
  7. NIST Engineering Statistics Handbook: What is experimental design? Primary guidance for planning controlled changes and measured responses so an experiment can support valid, objective conclusions.
  8. NIST Engineering Statistics Handbook: General design principles for process modeling Primary guidance identifying replication and randomized run order as core design principles that help estimate variation and distribute drift.
  9. NASA Glenn: Drag coefficient and the drag equation Primary educational reference for drag force, density, velocity, reference area, and drag coefficient. It explains physics, not Derby legality.
  10. NASA Glenn: Measuring aerodynamic drag Primary educational reference for calibrated force balances, tare measurements, and repeatable wind-tunnel drag tests.
  11. NASA Glenn: Similarity parameters and Reynolds number Primary educational reference for matching flow conditions; a small model can produce a different drag coefficient when Reynolds number is not representative.
  12. NASA Fastener Design Manual Engineering reference for threaded-fastener behavior. The torque-preload relation is used here only as a friction-sensitivity model, never as a Derby torque recommendation.
  13. NIST torque realization and calibration Primary reference for traceable torque realization and calibration; a wrench reading still does not directly measure clamp preload.

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