Terms & definitions
The Solo Rules define their own vocabulary in §12 — and those definitions apply "regardless of any other definitions or interpretations." Quoted or summarized below, alongside practical terms the rulebook uses without defining. Read §12 in the official PDF →
Defined by the rulebook (§12)
- Sedan§12
- “A car capable of transporting four (4) or more average-size adults in normal seating positions.” A functional definition, not a body style — a wagon, SUV, or hatchback that seats four adults is a sedan for rules purposes. This is why sedans-and-coupes catch-alls can apply to wagons.
- Mid-engine§12
- Engine located behind the passenger compartment and in front of the rear axle. Matters for BST tire-width limits (295mm vs 315mm).
- Open / closed car§12
- Closed: full roof, or targa/T-top with a full windshield. Open: convertible, retractable hardtop, or targa/T-top with less than a full windshield. Drives helmet and rollover requirements.
- Standard part§12
- Standard or optional equipment orderable with the car and delivered through a US dealer, including manufacturer options installed by dealers or ports. Dealer accessories don't count, and this definition does not allow update/backdate.
- Model§12
- Cars of a make with virtually identical bodies and chassis, distinguished from other models by major body/chassis differences — regardless of what the manufacturer calls them.
- Strut bar§12
- A transverse member connecting upper or lower suspension mounting points left-to-right. 2-point bars fasten only at the towers; triangulated bars add firewall attachments. All connections bolted.
- Drivetrain§12
- Engine, clutch, transmission, driveshafts, differentials, axles — the components that make the car move. Not wheels or spindles.
Practical terms
- Coupe
- Not defined in §12 — commonly read as a two-door fixed-roof car. Because “sedan” is defined functionally, the sedans-and-coupes catch-alls rarely turn on this distinction.
- Wagon / SUV
- Also not defined as body styles in the rulebook. If it seats four adults, it meets the §12 sedan definition; some (like all Subaru Foresters) appear on the §3.1 Street-category stability exclusion list, which is a separate question from body style.
- NOC — Not Otherwise ClassifiedAppendix A
- A car with no specific Appendix A listing. NOC cars class via category catch-alls and are Regional-only: ineligible for National Tours and the Solo National Championships.
- Catch-allAppendix A
- The listing at the end of a category's classes that sweeps up unlisted cars (by displacement/aspiration in ST, V8 sedans in FS, etc.). Per Appendix A: start from the last class in the category and work up until a class is found.
- Limited Prep / Full Prep§15
- Street Prepared's two tiers. Several classic SP modifications — radio removal, splitters, fender modifications, metal clutch/flywheel — are Full Prep only. Cars marked *Limited Prep* in Appendix A run SP with the reduced allowance set.
- 200TW / UTQG treadwear§13.3
- Street and Street Touring tires must carry a UTQG treadwear grade of 200 or higher, have at least 7/32″ molded tread depth, and be listed in the Tire Guide. Below 200TW (R-comps) means Street Prepared.
- Section width§14.3
- The tire's nominal width in millimeters (the 225 in 225/45R17). Street Touring classes cap it per class and drivetrain — 225mm (EST) up to 315mm (BST RWD N/A), unlimited in SST.
- §3.1 stability exclusion§3.1
- Vehicles with high centers of gravity and narrow track (SUVs, minivans, pickups) that fail the rollover guidelines must be excluded; Appendix A lists examples. A §3.1-excluded car can still appear in ST/SP listings — eligibility is per the rollover chart, so ride height matters.
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