Rules Desk
Maximum weight and scale math
Compare current ISBD and NDR total-weight frameworks, calculate axle distributions, and leave enough inspection margin for real race scales.
Car plus driverOrganization-specificScale margin matters
ISBD RACE-WEIGHT WINDOWS
The current championship classes use narrow scale bands.
| ISBD division | Combined race weight | Distribution rule | Rear range at maximum |
|---|---|---|---|
| Stock | 198-200 lb | Within 15 lb nose or tail | 92.5-107.5 lb |
| Super Stock | 238-240 lb | Within 15 lb nose or tail | 112.5-127.5 lb |
| Masters | 253-255 lb | Within 15 lb nose, 5 lb tail | 120-130 lb |
| Legacy | Maximum 275 lb | Plan and event inspection | Do not infer from kit classes |
The rear ranges are derived scale math at the maximum total, not separately printed official targets. At 200 pounds, for example, a 15-pound differential means 107.5 on one axle and 92.5 on the other.
NDR IS A DIFFERENT TABLE
Read the wheel-bank and event conditions.
| NDR division | Z-Glas maximum | Nationals aluminum-wheel scale | Live 2025 tail differential |
|---|---|---|---|
| Stock | 200 lb | 210 lb | 5 lb |
| Super Stock | 240 lb | 250 lb | 15 lb |
| Flat Masters | 255 lb | 265 lb | 5 lb |
| Roundbottom | 265 lb | 275 lb | 5 lb |
| Legacy | 273-275 lb on current Z-Glas inspection sheet | Verify for event | 15 lb |
SAFE BALLAST WORKFLOW
Secure, legal, documented weight wins inspection.
- Weigh the complete dressed driver and race-ready car on level, repeatable scales.
- Choose only the locations, plates, holes, bolts, and fasteners allowed by the exact plan.
- Keep weight fixed; never use loose shot, movable ballast, improvised chains, or cantilevered assemblies.
- Recheck driver clearance, steering, brake travel, floorboard integrity, and fastener engagement.
- Measure total and axle weights with the driver in the official position.
- Leave a practical margin below maximum for clothing, scale, and environmental differences.
rear load = (total + tail differential) / 2
front load = (total - tail differential) / 2
front load = (total - tail differential) / 2
A car that is legal by formula can still fail because the ballast shape, attachment, floorboard holes, driver position, wheel bank, or scale procedure is not legal.
SOURCES & FURTHER READING
Check the primary material.
- ISBD Rule Book - linked for the 2026 World Championship Official PDF currently linked from Race Week resources; the file itself says revised June 2025.
- ISBD: Adding weights to your car Official basic examples for Stock and Super Stock combined weight.
- National Derby Rallies rules hub Official NDR landing page, 2025 tail-weight update, rule books, and inspection links.
- NDR Nationals inspection sheets Current division inspection sheets are a practical pre-race checklist.