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How to Scale a Dirt Track Race Car

Introduction Scaling is how you measure and set the weight on each tire so your dirt car is balanced, predictable, and fast. If you’re new to grassroots racing—Street Stock, IMCA Modified, Sport Mod, Hobby Stock, or Late Model—this guide is for you. You’ll learn how to scale a dirt track race car correctly, what numbers to aim for, and how to avoid common beginner mistakes. We’ll cover tools, step-by-step procedures, and crew chief tips to build a reliable baseline you can repeat week after week.

How to Scale a Dirt Track Race Car: Why It Matters

Scaling tells you:

  • Corner weights: LF, RF, LR, RR
  • Left side percentage = (LF + LR) / total
  • Rear percentage = (LR + RR) / total
  • Crossweight (wedge) = (RF + LR) / total
  • LR bite = LR weight − RR weight (common in dirt)

Why it matters:

  • Consistency: A repeatable baseline makes setup changes meaningful.
  • Balance: Correct cross/LR bite gives entry stability and forward drive.
  • Tire life: Even load reduces overheating and cupping.
  • Safety: A car that doesn’t dart or snap loose is easier to drive hard.

On dirt, many teams tune around LR bite and rear percentage more than pure crossweight, but all four metrics matter.

Step-by-Step Guide: How Scaling Works

  1. Prepare the area
  • Use a level, rigid surface. Shim scale pads until they’re within 0.1° side-to-side and front-to-rear.
  • Zero scales with pads on. If you don’t have slip plates, put a thin plastic sheet with a little powder or two trash bags under each tire to reduce bind.
  1. Prepare the car
  • Race-ready: same springs, shocks, bar holes, wheelbase, gearing, seat, ballast, sway bar condition, and alignment you’ll run. Tighten everything.
  • Fuel: load your typical starting amount.
  • Tires: the exact wheels/tires you race, set to your hot target or a written “scaling pressure” you use consistently. Set stagger as raced.
  • Driver: sit in the car with full gear. If not possible, add ballast equal to driver weight in the seat.
  • Steering: wheels straight ahead; center the box.
  1. Set baseline ride heights
  • Put the car on the pads. Set ride heights to your class baseline (front, crossmember, and rear frame heights). Record them. This is your “race attitude.”
  1. Settle the suspension
  • Bounce each corner or roll the car forward and back a foot on the pads to free bind. Let shocks settle before reading.
  1. Record weights and calculate
  • Write LF, RF, LR, RR and total.
  • Left% = (LF + LR) á total × 100
  • Rear% = (LR + RR) á total × 100
  • Cross% (wedge) = (RF + LR) á total × 100
  • LR bite = LR − RR (in pounds)
  1. Make adjustments in order
  • Rear% and Left% are best changed by moving ballast (within rules), battery, fuel, or heavy components. Big changes with jack bolts will move ride heights.
  • Crossweight/LR bite are changed with jack bolts or coilover preload:
    • Increase cross or LR bite: add turns to RF and/or LR (or remove from LF/RR).
    • Decrease cross or LR bite: add turns to LF and/or RR (or remove from RF/LR).
    • Typical sensitivity: 1/6 turn (one flat) on a 1/2-13 jack bolt moves roughly 5–10 lb at that corner. Work in small steps.
  • After every change, re-settle the car, re-check ride heights, and re-measure.
  1. Re-check zero-preload items
  • Sway bar: set to zero preload at race attitude unless your setup calls for preload.
  • Four-link/birdcages: index neutral at ride height unless your rules/setup specify preload.
  • Pull bar/third link: confirm neutral at ride height per manufacturer.
  1. Document your baseline
  • Record all numbers: tire pressures, ride heights, each corner weight, left/rear/cross, LR bite, bar holes, shock clicks, spring rates. This becomes your “Heavy” or “Dry-Slick” page.

Suggested baselines (general starting points; confirm class rules and chassis builder):

  • Street Stock/Hobby Stock
    • Left%: 53–55
    • Rear%: 50–54
    • Cross%: 49–52
    • LR bite: 25–75 lb (track-dependent)
  • IMCA Modified/Sport Mod
    • Left%: 54–56
    • Rear%: 53–56
    • Cross%: often ends up 49–52
    • LR bite: 25–75 lb (heavy) to 75–125 lb (dry-slick)
  • Dirt Late Model
    • Left%: 56–59
    • Rear%: 55–58
    • LR bite: 50–150 lb depending on track grip

Track tendencies:

  • Heavy/tacky: slightly less LR bite and/or cross to keep the car free.
  • Dry-slick: more LR bite or a tick more cross for forward drive and stability.

Key Things Beginners Should Know

  • Scale it as you race it: same fuel, driver, wheels/tires, ride heights, bar holes, shock settings.
  • Tire pressures first: do not chase scale numbers until pressures are exact.
  • Settle the car: roll or bounce before reading every time.
  • Keep steering straight: off-center steering adds scrub and changes readings.
  • Static vs dynamic: scaling gives a static snapshot. Bars, shocks, and throttle steer change loads dynamically; scale numbers are a starting point.
  • Work from “big to small”: ballast and components for left/rear%; jack bolts for cross/LR bite; then fine-tune with shocks and bars at the track.
  • Record everything: repeatability beats guessing.

Safety notes

  • Use quality jack stands when adjusting; never crawl under a car supported by a jack alone.
  • Keep hands clear of springs and rotating parts while settling the car.
  • Verify ballast is securely mounted with proper hardware and lock nuts.

Equipment, Gear, and Costs

Must-haves

  • 4-pad race car scales (wired or wireless)
  • Accurate tire pressure gauge
  • Tape measure, digital angle finder, and ride height gauges
  • Notepad or setup sheet

Nice-to-haves

  • Slip plates or plastic/bag “sliders”
  • Setup plates and turn plates
  • Smart level/laser level for pad setup
  • Camber/caster gauge and toe plates

Costs and options

  • Used wired scales: $800–$1,500
  • New wireless scales: $1,500–$3,000+
  • Budget tip: many tracks/shops rent scales or let you scale on a flat pad for a small fee.

What you don’t need

  • Fancy software to start. A consistent checklist and notebook beat inconsistent high-tech.

Expert Tips to Improve Faster

  • Build two baselines: “Heavy” and “Dry-Slick” setup sheets. Scale and save both.
  • Mark adjusters: paint-mark jack bolts and note “+1 flat = ~7 lb” for your car.
  • Keep it square: verify wheelbase left/right and rear-end thrust angle before scaling.
  • Check bind: shocks should move smoothly; birdcages rotate freely at ride height.
  • Control variables: scale in the same bay, tire pressures, fuel load, and order every time.
  • Re-zero the sway bar: with driver in, at ride height, before final readings.
  • Post-race audit: mud adds weight—wash first. If the car drove great, scale it and save the numbers.

Common Beginner Mistakes

  • Scaling without the driver or without proper fuel load
  • Chasing crossweight with tire pressures instead of jack bolts
  • Ignoring ride heights after making adjustments
  • Unlevel scale pads or a soft floor that flexes
  • Steering not centered while scaling
  • Preloaded sway bar or four-link unintentionally
  • Making multiple big changes at once without notes

FAQs

Q: Should I disconnect the sway bar when scaling? A: Scale the car as raced. Set the sway bar to zero preload at ride height with the driver in, then tighten the links.

Q: What’s better to target on dirt: crossweight or LR bite? A: Most dirt teams use LR bite as the main target and let cross end up where it lands. Still record cross; it’s a useful reference.

Q: How much will one turn on a jack bolt change weight? A: On many cars, one flat (1/6 turn) moves roughly 5–10 lb at that corner. Always recheck ride height and settle the car.

Q: Do I scale with hot or cold tires? A: Be consistent. Many teams use a standard “scaling pressure” cold, written on the setup sheet, so results are repeatable.

Q: Can I scale on concrete that isn’t perfectly level? A: Yes, if you shim all four pads level and in the same plane. A smart level or laser helps. Don’t trust the floor—trust the pads.

Q: How often should I scale? A: After big repairs, spring or shock changes, major hits, or noticeable handling changes. Otherwise, audit every few race nights.

Conclusion Scaling isn’t mystical—it’s methodical. Set tire pressures, level your pads, put the car in race attitude with the driver and fuel, record the numbers, and make small, documented changes. Build a repeatable baseline, then tune for track conditions. Do it right and the car will be easier to drive, faster, and more consistent from hot laps to the checkered flag.

Optional suggested images

  • Overhead photo of a car on four scale pads with labels LF/RF/LR/RR
  • Close-up of a setup sheet showing left%, rear%, cross%, LR bite
  • Diagram showing which jack bolts to turn to increase or decrease cross/LR bite
  • Photo of slip plates or “trash bag” method under tires
  • Shot of sway bar links being set to zero preload at ride height