USRA B-Mod body rules

Anything between the nose fins, or anything that separates from the hood, counts as nose. No part of the nose can sit in front of the front bumper. (Rules 1.15, 1.19.5, Diagram V)

Nose

• Rule 1.15, Diagram N Nose width: 42 in max, at the top and at the bottom. (Rule 1.15, Diagram N)
• Rules 1.15, 1.19.7, Diagram A1 Nose length: the front of the nose and the front bumper can each reach no more than 42 in ahead of the center of the lower ball joints. Rule 1.15 gives the nose length with no tolerance. Diagram A1 measures the 42 in for both from the front wheel center. (Rules 1.15, 1.19.7, Diagram A1)
• Rules 1.15, 1.14, Diagrams F, U Keep the nose flat and parallel to the deck (the flat top of the body behind the hood; on a B-Mod it starts at the rear of the engine block and runs back over the cockpit to the rear of the car). No concave nose, whatever it's made of. (Rules 1.15, 1.14, Diagrams F, U)
• Rule 1.15 Fins. 2 in fins are allowed along both sides of the nose and must match side to side. They can't reach past the leading edge of the radiator or the leading edge of the hood. (Rule 1.15)
• Rules 1.15, 1.19.5 Nose and bumper. All aluminum in the nose, fins included, stays inside the outer edges of the front bumper. Plastic can flare out past the bumper's sides. (Rules 1.15, 1.19.5)
• Rules 1.15, 1.19.5 Plastic nose pieces and plastic valances (panels under the nose) are allowed, part #MD3M21100. With a plastic nose, put a horizontal brace in the upper nose filler every 12 in so the panel can't cave in. (Rules 1.15, 1.19.5)
• Rules 1.18, 1.19.5, Diagram Q Nose to ground: every part of the nose piece at least 5 in off the ground. (Rules 1.18, 1.19.5, Diagram Q)

Bumpers

• Rule 1.19.2 You need a front and a rear bumper, with no sharp edges. Officials can turn away any bumper they find unfit. (Rule 1.19.2)
• Rule 1.19.2 Bumper tubing: at least 1.25 in diameter with 0.065 in wall, front and rear. Each bumper has to hold the car's weight when a tow vehicle lifts it. (Rule 1.19.2)
• Rule 1.19.1, Diagram T Bumper center height: between 16 and 20 in off the ground, front and rear. (Rule 1.19.1, Diagram T)
• Rule 1.19.2 Mount the front bumper from one frame end to the other, with the bottom loop parallel to the ground. (Rule 1.19.2)
• Rule 1.19.2 On a bumper with a top bar and a bottom bar, the top bar sits straight above the bottom bar, not off center. (Rule 1.19.2)
• Rule 1.19.6 Front bumper width: 46 in max, outside to outside. (Rule 1.19.6)
• Rules 1.19.3, 1.19.4 The rear bumper's own rules (width and fuel cell protection) are under Deck and spoiler. (Rules 1.19.3, 1.19.4)

The hood sits no more than 2 in above the deck and is sealed off from the driver. (Rule 1.9)

Hood

• Rule 1.9, Diagram V The hood is level or slopes down toward the nose. No reverse rake (a hood that rises toward the nose). (Rule 1.9, Diagram V)
• Rule 1.9 Flat from side to side: no bowed or concave hood and no lips. (Rule 1.9)
• Diagram I Hood sides: 6 in max, top to bottom. (Diagram I)
• Diagram I Hood slope: 3 in max, the drop toward the nose. (Diagram I)
• Diagram M Hood item M: 6 in max. Diagram M marks a raised piece on top of the hood, drawn as a scoop, and doesn't name the part. (Diagram M)
• Rule 1.18 No engine covers. (Rule 1.18)
• Rule 2.9 Brace bars ahead of the roll cage can't sit higher than the "stock hood height". (Rule 2.9)

Engine placement

• Rules 3.11, 12.6 Engine setback: the rear of the engine (the bell housing flange) at least 72 in ahead of the rear axle centerline, no tolerance. (Rules 3.11, 12.6)
• Rule 13.4 Engine offset: the front and the rear of the engine within 2 in of the centerline of the front crossmember. (Rule 13.4)
• Rules 13.4, 1.14 Keep the engine square in the chassis, or skew the rear of the engine to the left only. A skewed engine still has to stay within rule 1.14, the deck rule (see Deck skew under Deck and spoiler). (Rules 13.4, 1.14)

• Rule 13.5 Crankshaft height: the front center of the crankshaft at least 11 in off the ground. (Rule 13.5)

Apart from the hood and nose, no part of the body can reach farther forward than the back of the engine block. The one exception is the bottom of the door, which can run up to 8 in ahead of the rear of the block. (Rule 1.17, Diagram G)

Doors and quarter panels

• Diagram F The top of the door and the deck start at the rear of the engine block. (Diagram F)
• Rule 1.14, Diagram C1 Door height: the doors and quarter panels (the body sides behind the doors) have between 22 and 36 in of material length, bottom edge to the deck. Diagram C1 calls for doors at least 22 in tall. (Rule 1.14, Diagram C1)
• Rule 1.14 Doors and quarter panels sit flush with the deck and stay outside the outside frame rails. (Rule 1.14)
• Rule 1.14 The rear edge of each rear quarter panel is square to its top edge. It can't run past the rear of the deck or tuck under it. (Rule 1.14)
• Rule 1.11 No panel in front of the right door, beside the engine compartment. (Rule 1.11)
• Rule 1.18 Panel break: a bend of up to 0.5 in for stiffness is allowed on body panels. (Rule 1.18)
• Rule 13.4.2 No exhaust out through the body panels or fenders. (Rule 13.4.2)

Skirts and ground clearance

• Rule 1.18 Plastic skirt (a strip added along the bottom edge of a panel): up to 5 in on the bottom of the doors, the quarter panels and the nose piece. (Rule 1.18)
• Rule 1.18, Diagrams S, *** Body to ground: the body, doors and quarter panels at least 3 in off the ground. (Rule 1.18, Diagrams S, ***)

Car width

• Rules 1.16, 1.19.3 The tires are the widest part of the car. No part of the body can stick out past the outside edge of the tires. (Rules 1.16, 1.19.3)
• Rule 1.16 Exception: the lower front edge of the left-rear quarter panel's wheel opening can sit up to 1 in outside the tire. The opening can't be smaller than the tire's outside diameter. (Rule 1.16)
• Rule 1.19.3 Side rail bars (nerf bars, the tube bars outside the body) can't reach past the width of the rear tires. (Rule 1.19.3)
• Rules 3.10, 8.1.8 Car width: 78 in max across the widest points on each side, which are the tires. Measure from the top of the left tire across to the bottom of the right tire. (Rules 3.10, 8.1.8)
• Rule 8.1.8 Spacers between the hub and wheel are allowed if they're aluminum, but the 78 in still holds. (Rule 8.1.8)

Door bars and door plate

• Rule 2.1 Driver side: at least 3 door bars (the horizontal cage tubes beside the driver), parallel to the ground and square to the driver, welded to the cage at the front and the rear. They have to protect the driver without making it unduly hard to get in or out. (Rule 2.1)
• Rule 2.1 Driver-side door bars and uprights: at least 1.5 in diameter with 0.083 in wall. (Rule 2.1)
• Rule 2.1 Door plate: steel, at least 18-gauge (0.049 in), welded securely to the outside of the driver-side door bars. It covers from the top door bar to the bottom door bar, and from the rear hoop down post to 5 in ahead of the seat. (Rule 2.1)
• Rule 2.1 Passenger side: at least 1 cross bar, horizontal or angled, of at least 1.25 in OD with 0.083 in wall, plus 1 top horizontal bar of at least 1.5 in OD with 0.083 in wall. (Rule 2.1)

Keep the roof line parallel to the deck, front to back and side to side, apart from the slope allowed below. (Rule 1.6)

Roof

• Rule 1.6, Diagram * Roof slope: 5 in max, rear to front. With a level laid on the roof, the gap is at most 5 in at the front and 2 in at the rear. (Rule 1.6, Diagram *)
• Rule 1.6, Diagram C2 Car height: 56 in max, measured from the ground up to the car's highest point. (Rule 1.6, Diagram C2)
• Diagram K Roof length: between 40 and 56 in. (Diagram K)
• Diagram L Roof width: between 44 and 50 in. (Diagram L)
• Rule 1.6 Rear roof stiffener: up to 1 in, turned down square to the ground. (Rule 1.6)
• Rule 1.6 Roof lips: up to 1 in on the outside edge of the roof. (Rule 1.6)
• Rule 1.6 Roof sides: vertical sides up to 4 in. (Rule 1.6)
• Rule 1.6 Roof fasteners: up to 4 on the rear edge of the roof. (Rule 1.6)
• Rule 1.6 Fiberglass roofs are allowed. Aluminum roofs are allowed if they stay flat, never concave. (Rule 1.6)

Pillars and windshield

• Rule 1.3 Front window supports. The posts on each side of the windshield opening have to look like a production car's. A painted roll bar doesn't count. (Rule 1.3)
• Rule 1.3, Diagram R Windshield base: the front window support can measure up to 20 in at the base of the windshield, from the cowl (the panel between the hood and the windshield) back, and runs straight up to the top of the opening. (Rule 1.3, Diagram R)
• Rule 1.5 The windshield opening and its corner posts keep a standard shape, with no streamlining across the top. (Rule 1.5)
• Rule 1.2 Half windshield: an aluminum half windshield is allowed on the driver's side of the front opening only, reaching no more than 6 in past the steering wheel. (Rule 1.2)
• Rule 2.7 A screen or bars are required in the front window opening, in front of the driver's face. (Rule 2.7)

Windows

• Rule 1.4 Window openings: every opening, front, back, left and right, at least 12 in. (Rule 1.4)
• Diagram H The side window opening, top of the door to the roof, is between 12 and 18 in tall. (Diagram H)

Sail panels

Sail panels are the side panels running from the roof back to the deck. Build them solid, as a matched pair, the same design and style on both sides. (Rule 1.7)

• Rule 1.7 Where it sits. Mount each panel within 1 in of the deck's outer edge and flush with the roof's outer edge. It can't run past the rear of the deck or rise above the roof. (Rule 1.7)
• Rule 1.7 How far forward. Rule 1.7 says a sail panel can start no farther forward than the driver's seat. The Sail Panels drawing on the body diagram says no farther forward than the rear of the seat. (Rule 1.7)

• Rule 1.8 Shape. Held flat, the top edge is a straight line from the back edge of the roof to the back edge of the deck. (Rule 1.8)
• Rule 1.8 Sail along roof: 18 in max. (Rule 1.8)
• Rule 1.8 Sail height at rear: 5 in max above the deck at the rear of the deck. (Rule 1.8)
• Rule 1.8 Sail leading edge: within 2 in of 90 degrees, from the roof down to the quarter panel. (Rule 1.8)
• Rule 1.8 Sail bow: up to 4 in of outward bow, consistent from top to bottom. Never concave. (Rule 1.8)
• Rule 1.7 Sail side to side: the left and right panels' material lengths, roof line to deck, can differ by no more than 4 in. (Rule 1.7)
• Rules 1.8, 1.13 At a track that has adopted USRA's Article 17 alternative rules, a car running a spoiler under that article can have sail panels up to 43 in long. (Rules 1.8, 1.13)

Window net

• Rule 15.13 A full-size window net is required in the driver's window opening on the left side, with its mounts welded to the roll cage. (Rule 15.13)
• Rule 15.13 Recommended: approved racing arm restraints. (Rule 15.13)

The deck covers the trunk area completely. No drop decks, and never concave. (Rule 1.14)

Deck

• Rule 1.14, Diagram D Deck height: 39 in max off the ground, no tolerance. (Rule 1.14, Diagram D)
• Rule 1.14, Diagram E Deck length: 120 in max, from the rear of the engine to the rear of the deck. (Rule 1.14, Diagram E)
• Rule 1.14, Diagram J Deck width: between 53 and 66 in, the same from front to rear. Rule 1.14 sets no more than 66 in; the 53 in minimum comes from Diagram J. (Rule 1.14, Diagram J)
• Rule 1.14 Keep the deck parallel to the frame and chassis, with its front edge level to the ground from side to side. The skew and the rake below are the allowed departures from parallel. (Rule 1.14)
• Diagram U Diagram U keeps the deck flat from side to side except over the cockpit. (Diagram U)
• Rule 1.14, Diagram W Deck skew: the skew is measured from a line parallel to the motor. At the rear of the deck, the deck can sit up to 4 in to the right of that line. Diagram W puts the rear of the deck within 4 in of the front of the deck, measured from that same line. (Rule 1.14, Diagram W)
• Rule 1.14, Diagram U Deck rake: rule 1.14 allows up to 6 in of total slope, measured from the ground, with no more than 3 in of it from the racing seat to the rear of the deck, on every car. Diagram U allows up to 6 in of rake front to rear and applies the 3 in, measured from the rear of the racing seat, only when the doors are flat. (Rule 1.14, Diagram U)

• Rule 1.11 No panels mounted under the deck, flat or upright. (Rule 1.11)

Spoiler

• Rules 1.13, 1.18 No spoilers. No fins, wings, lips or other air spoilers beyond the ones the rules name, and any allowed lip must match side to side. (Rules 1.13, 1.18)
• Rule 1.13 At a track that has adopted USRA's Article 17 alternative rules, a car can run a spoiler of up to 3 in if it follows that article's list. The list requires an 8 in rear filler panel and also sets rules for the rear suspension, engine, rear end, transmission and wheels. (Rule 1.13)
• Rule 1.13 The track needs USRA's approval and has to decide before the season, then advertise the option and post it on its website. It can drop the option at any time, and drivers can't pick it race by race. (Rule 1.13)
• Rule 1.13 Article 17 also lets cars at those tracks run the Wissota Midwest Modified rules instead, with no spoiler. Cars can't mix the two sets of rules. (Rule 1.13)

Fuel cell

• Rule 1.14 Access panel: at least 6 in wide by 12 in long, in the deck ahead of the fuel cell, so tech can see where the pull bar (a rear suspension part) sits. (Rule 1.14)
• Rule 7.4.1 Use a commercially made fuel cell, held by at least 2 steel straps that are 2 in wide at every measuring point. (Rule 7.4.1)
• Rule 7.4.2 Enclose the cell in a steel container. Behind the axle, protect it with securely mounted roll cage tubing. (Rule 7.4.2)
• Rule 7.4.3 Fuel cell height: the lowest point of the cell at least 10 in off the ground, and no part of it lower than the protective tubing. (Rule 7.4.3)
• Rule 7.4.3 Fuel cell tubing: the protective tubing can be no wider than 6 in on each side. (Rule 7.4.3)

• Rule 7.4.4 Check valves are required. A cell without a positive-seal filler neck and cap needs a ball-type, flapper, spring or filler rollover valve. (Rule 7.4.4)
• Rule 7.4.5 Capacity: no more than 32 gallons. (Rule 7.4.5)
• Rules 1.19.3, 1.19.4 The rear bumper can be round tubing. It must protect the fuel cell and can't reach past the width of the rear tires. (Rules 1.19.3, 1.19.4)

The driver's compartment needs a complete floor and a complete firewall, and the driver must be able to climb out on either side. (Rule 4.4)

Firewall and floor

• Rule 4.4 Floor pan: a complete pan, at least 0.125 in aluminum or 0.060 in steel. (Rule 4.4)
• Rule 1.9 Seal the hood off from the driver, as under Hood and engine bay. (Rule 1.9)
• Rule 4.4 Firewall: complete across the driver's compartment. The rulebook gives no metal or thickness for it. (Rule 4.4)
• Rule 15.15 The firewall itself can't be plastic. Plastic is allowed only from the firewall's edge out to the body skin; the full plastic rule is under Body and panels. (Rule 15.15)

Interior sheet metal

• Rule 4.4 Interior sheet metal can't rise above the window openings (see Windows) or close one in. (Rule 4.4)
• Rule 4.4 From the top of the driveshaft tunnel, run the sheet metal level over to the right-side door bars, or angle it up to the top of those bars. (Rule 4.4)
• Diagram ** If that sheet metal (the interior shield) looks too large or unsafe, officials can ask the driver to climb out the right side with a helmet on. (Diagram **)

Seat position

• Rule 4.6.3 Seat back: no farther back than the rear edge of the quarter post (on a street car, a roof post that rises from the quarter panel). (Rule 4.6.3)

• Rule 4.6.3 Mount the seat with fasteners of at least 3/8 in, with washers. (Rule 4.6.3)

Cage-to-body fit

• Rule 2.1 Cage tubing: the main four-point cage is continuous hoops of round steel tubing, at least 1.5 in diameter with 0.095 in wall, and officials have to accept it. (Rule 2.1)
• Rule 2.1 Tubing of 1.75 in diameter can use 0.083 in wall; tubing under 1.75 in needs at least 0.095 in wall. (Rule 2.1)
• Rule 2.1 No sliding or slip-joint unions in the main cage. (Rule 2.1)
• Rule 2.5 Build the cage from front and rear hoops joined by side tubing, or from side hoops, all meeting the tubing sizes above. (Rule 2.5)
• Rule 2.4 Cage mounts: mount the cage to the frame in at least 6 places. (Rule 2.4)
• Rule 2.6 With the helmet on and the driver belted into the seat, the top of the driver's head can't stick up above the cage. The halo (the top hoop over the driver) needs a cross bar. (Rule 2.6)
• Rule 2.8 Foot protection. Required: a bar across the back of the engine, plus vertical bars and rub rails (strips along the body side that take contact) or similar protection. (Rule 2.8)
• Rule 2.10 No adjustable bars on the frame or the cage. Removable bars are allowed. (Rule 2.10)
• Rules 2.2, 15.13 Pad every roll bar within the driver's reach with a material officials accept, and every bar around the driver with approved roll bar padding. (Rules 2.2, 15.13)
• Rule 2.2 Recommended: fire-retardant padding. (Rule 2.2)
• Rules 2.1, 2.3, 2.11 Officials have to accept the cage's installation and workmanship. A cage that breaks these rules can draw cash fines and other penalties. (Rules 2.1, 2.3, 2.11)

Use only a factory-production frame: a complete, full-perimeter frame from a 1960 or newer American passenger car, with parallel rails. A full-perimeter frame is a separate frame that runs all the way around the car under the body. You can cut off its rear, as set out under Allowed frame changes. (Rule 3.1)

Which frame

• Rule 3.9 No tubular front clips. The front clip, or front stub, is the section of the frame ahead of the firewall. (Rule 3.9)
• Rule 3.4 Frame sheet. USRA publishes a separate Modified and B-Mod frame diagram (the frame sheet), drawn on a 1968-1972 GM Chevelle frame. Rule 3.4 says every measurement on it must fall within its listed range. Frame tolerance: any measurement the sheet doesn't list must be within 0.5 in either way of OEM (the original factory frame), no tolerance. (Rule 3.4)
• Rule 3.4 Front frame width (sheet item C): from the centerline to the outside of each front stub rail behind the crossmember, between 27.50 and 28.25 in. That range is for the Chevelle frame; on other frames, stay within 0.5 in of OEM. (Rule 3.4)

Allowed frame changes

• Rules 3.1, 3.3, 3.4 Cutting the rear. You can cut the frame only at the rear, at or behind the rear of the engine. Every frame part, including anything you add behind the cut, is steel and properly welded, and the frame still has to be full and complete on both sides and able to carry the roll cage on both sides. (Rules 3.1, 3.3, 3.4)

• Rule 3.4 No widening or narrowing, and leave every factory hole in place for inspection. (Rule 3.4)
• Rules 3.2, 3.6 Other changes. Apart from cutting the rear and the radiator notch below, you can alter the frame only to mount springs and shocks, and the rear of the frame can be altered to take leaf or coil springs. You can't alter the top of the frame for upper A-frame clearance (room for the upper control arms). (Rules 3.2, 3.6)
• Rule 3.5 You can notch the front crossmember, for radiator clearance only. (Rule 3.5)
• Rules 3.4, 3.5 The outside frame rails can't be raised. Tech checks this with the front rail check (sheet item L) on the outer front rail: the bottom of the marked frame hole sits between 5.5 and 6.5 in above the bottom of the frame, 6 in nominal. (Rules 3.4, 3.5)

Wheelbase, ride height and weight

• Rule 3.8, Diagram A2 Wheelbase: between 108 and 112 in on both sides, no tolerance. Wheelbase is the distance from the center of the front hub to the center of the rear hub. (Rule 3.8, Diagram A2)
• Rule 3.5, Diagrams P, *** Frame height: at least 4 in off the ground, apart from the radiator notch in the front crossmember (see Allowed frame changes). (Rule 3.5, Diagrams P, ***)
• Rules 13.8.18, 14.1, 14.2 Car weight: at least 2,500 lb, weighed at the end of the event with the driver in the car in full racing gear. The concept engine rules repeat the same 2,500 lb minimum. (Rules 13.8.18, 14.1, 14.2)
• Rule 14.3.1 Mount ballast only to the frame, the roll cage or the rear-end housing. Weight brackets on the rear-end housing are steel. (Rule 14.3.1)
• Rule 14.3.1 No ballast in the cockpit or on any rotating or suspension part, and none outside the body or hood area. (Rule 14.3.1)

• Rule 14.3.2 Bolt ballast on securely, paint it white and mark it clearly with the car number. (Rule 14.3.2)
• Rule 14.3.3 Fasten each piece with at least 2 bolts of 0.5 in, with no more than 100 lb per mounting. A piece of 25 lb or less can use 1 bolt of 0.5 in. (Rule 14.3.3)
• Rule 14.3.4 No ballast on the rear bumper. (Rule 14.3.4)

Under the car

• Rule 1.10 No belly pans. The rulebook counts any object or material that changes the airflow under the car as a belly pan. (Rule 1.10)

The rulebook names no body style or approved body kits for this class, so you build the body to the shapes and measurements in the topics above.

Panel materials

• Rule 1.1 No plastic or composite body panels, except the doors and rear quarter panels, which can be fire-retardant plastic or composite. (Rule 1.1)
• Rules 1.6, 1.15, 1.18 Other parts the rules allow in plastic or fiberglass: the plastic nose piece and valances, plastic skirts up to 5 in and fiberglass roofs. (Rules 1.6, 1.15, 1.18)
• Rules 1.1, 15.15 Rule 15.15 bans plastic except from the edge of the firewall to the body skin and from the inner wheel tubs (the inner wheel wells) to the body skin. The parts Article 1 allows by name are the exceptions to it. (Rules 1.1, 15.15)

Damage

• Rule 1.12 Officials can keep a car with excessive body damage from racing. (Rule 1.12)

Numbers and appearance

• Rule 1.20.1 Numbers. Every car carries large, readable numbers on both sides, on the roof, on the nose and on the rear panels. (Rule 1.20.1)
• Rule 1.20.1 Side numbers. These should contrast with the body color and be at least 18 in tall and 4 in thick (the width of each stroke). (Rule 1.20.1)
• Rule 1.20.1 Roof numbers. These should be at least 24 in tall and 4 in thick. (Rule 1.20.1)
• Rules 13.6.4, 13.8.19 Engine decals near the A pillar (the windshield post): a factory-sealed crate engine needs a "Crate" decal in plain view, and a concept engine needs a "Concept" decal in plain view. (Rules 13.6.4, 13.8.19)
• Rule 1.20.2 Advertising. Officials can assign, approve or turn down any advertising, sponsorship or similar deal tied to an event, for the public image of the sport or of USRA. (Rule 1.20.2)
• Rule 1.20.2 Neat cars. Every car must look neat, and officials approve each car to race. By racing, you agree to follow their decisions on this. (Rule 1.20.2)