Afton Motorsports Park Modified and Sportsman Class Rules

The Modified and Sportsman class rules for Afton Motorsports Park are listed on this page. 2015 changes in red.

Forms: [Driver Sponsor Sheet]


Page 1 of Rules: [Go to Page 1] Includes Seat and Seat Belts, Driver's Equipment, Fuel, Ancillaries

Page 2 of Rules: [Go to Page 2] Includes Body, Body Style and Dimensions, Body Materials, Roof, Front Door Posts, Rear Wing Windows (Dirt Style Bodies), Body Width and Ground Clearance, Door Panels, Rear Quarter Panels, Rear Spoiler, Rear Deck

Page 3 of Rules: [Go to Page 3] Includes Hood, Nose and Front Spoiler, Hood Scoop, Interior Sheet Metal, Numbers, Driver Name, Sail Panel, Frame, Seat, Radiator, Engine, Transmission, Driveline, Rear End

Page 4 of Rules: [Front End] [Wheelbase and Tread] [Suspension] [Springs] [Shocks] [Brakes] [Front Bumper] [Rear Bumper] [Rub Rails] [Mufflers and Exhaust System] [Ballast Weight] [Battery] [Wheels] [Tires] [Minimum Weights]

[PDF of Modified and Sportsman Rules] [Download Adobe Acrobat]


  1. The front axle must be straight, one-piece steel tubing only with no camber adjustments.
  2. No split axle or dropped axle permitted.
  3. All brackets on the front axle must be bolted or welded (no bird cages or slides).
  4. Modified type front spindles only.
  5. It is recommended that bearing shafts be made of steel.
  6. Chassis may not be offset any more than 4" from center of inside tire width, measured from the inside of the left front tire to the inside of the right front tire at axle height.
  7. Front wheels must be fully exposed. No fenders are permitted.

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  1. Wheelbase: minimum 106", maximum 110". This measurement will be taken from the center of the rear axle to the center of the front axle, for both left and right sides with a maximum tolerance of 1/2".
  2. Tread width Modified and Sportsman: front - maximum 86", minimum 74".
  3. Rear tread, maximum 86", minimum 80".


  1. No independent suspensions front or rear.
  2. No "A" frames or ball joints may be utilized for steering axis (kingpin only).
  3. No four wheel steering permitted that is actuated by steering wheel.
  4. All suspension systems must be mechanical with no form of hydraulic, air, electrical, radio, or computer assistance for adjustments, in or out of cockpit allowed!
  5. No form of traction control is permitted. Braking system included!
  6. With the exception of brake bias and the rear pan hard, no other form of cockpit adjustment is permitted.
  7. Sportsman: May not have rear pan hard cockpit adjustment.


  1. Any form will be permitted (torsion bars, coil-overs, leaf springs, etc.).
  2. No carbon fiber or titanium springs are permitted.

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  1. Only one shock per wheel.
  2. Shocks may not be externally adjustable.
  3. External reservoirs are not permitted.
  4. Manufacturers must submit shocks for approval 2 weeks prior to being raced.
  5. All shocks used MUST be freely available to all competitors. Failure to easily purchase a type of shock could result in those shocks not being permitted.


  1. All cars must have four wheel hydraulic brakes in good working condition.
  2. No carbon fiber, carbon, titanium, ceramic or aluminum pads or rotors are permitted.
  3. On live rear axles, one inboard and one outboard brake assembly is permitted.
  4. Brake tests may be conducted throughout the year.
  5. Brake bias may be cockpit adjustable.


  1. Must be made from round steel tubing only, with a minimum diameter of 1 1/4" by .095 wall thickness for main bumper and all bracing.
  2. It must consist of two rails, an upper and lower and at least 1or 2 vertical braces equally spaced. These rails must have four sockets or supports attached to the frame.
  3. The four tubes that support the bumper from the four frame sockets must be horizontal. These rails must also be a minimum of 6" apart and a maximum of 12" measured from top to bottom and maintain that measurement for a minimum width of 24" or a maximum width of 30". It must also have an 18" center measured from the ground up to the middle of the bumper.
  4. The front bumper may not extend more than 24" in front of front axle center centerline.
  5. No V-shaped bumpers, crash area must be flat and vertical for the full width of bumper.
  6. The bumper must have all rounded ends and no sharp edges.
  7. The end bracing tubes of the bumper must be angled in such a way as to prevent the bumper interlocking with another cars bumper.

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  1. The rear bumper must be made of round steel tubing, with a minimum diameter of 1 1/2" by .095" wall thickness for main bumper and all bracing.
  2. It must consist of two rails, an upper and lower, which must have four sockets and horizontal support bars attaching it to the frame. These rails must also be a minimum of 10" apart and a maximum of 16" measured from top to bottom and maintain that measurement for a minimum width of 64" or a maximum width of 86".
  3. The rear bumper or any side bars cannot extend past the outside of tire sidewalls on both sides. It also must have an 18" center measured from the ground up to middle of bumper.
  4. The rear bumper may not exceed 52" back of the rear axle centerline.
  5. No V-shaped bumpers, crash area must be flat and vertical for the full width of bumper.
  6. Bumper must have all rounded ends and no sharp edges.


  1. The rub rails must be made of round steel tubing, with a minimum diameter of 1 1/2" by .095" wall thickness.
  2. All bracing must also be a minimum of 1 1/2" outside diameter by .095" wall thickness.
  3. Maximum wall thickness must be .095" with no solid bars or ballast added inside.
  4. Rub rails must be outside of body panels but may not exceed the outside edge of the tires. The exception is the left rub rail only, which may extend an absolute maximum of 2" outside the left rear tire sidewall.
  5. Rub rail ends must be rounded with no sharp edges and bent at a gradual 90 degrees and must protrude a minimum of 6" back in past the body.
  6. Rub rails must be a minimum of 50" long, socket to socket.
  7. 5/16"attachment bolts with nylon nuts or approved quick release solid pins are the only permitted fasteners. NO COTTER PINS!
  8. All 3 rub rail sockets must be pinned or bolted.
  9. Front and rear rub rails must have a 360 deg. sleeve 3/8" wide x .095" wall min. welded to the rub rail tube butted up against the support socket to prevent pins from shearing.


  1. Each car must have one unaltered muffler per bank.
  2. Mounting position front to back will be optional however the exhaust must exit past the driver.
  3. Each muffler must have a tail pipe no less than 10" long measured off the back of the muffler and must direct the exhaust to the rear of the car only so as to disturb as little dust as possible.
  4. No exhaust pipe may face outside the car.
  5. Modified - any manufacturer of exhaust header is permitted, but header material is limited to steel or stainless steel from the 300 series.
  6. Approved mufflers mandatory.
  7. Header collector extension pipe and tail pipe must not be inserted past the muffler inlet or outlet flange.

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  1. Any ballast weight used must be mounted within the vertical planes formed by the frame rails, must be securely fastened, and must remain stationary while racing.
  2. Weight may be added prior to the event or time trial.
  3. No weight pack may exceed 75 pounds.
  4. All weight packs must have a minimum of two 1/2'' securing bolts/studs of grade 5 or higher. These bolts/studs must be securely anchored to the frame by a suitable clamp.
  5. No bolts / studs welded to the frame will be permitted.
  6. Clamp around weights is permitted.
  7. All weights must be painted white and carry the car number in a legible fashion. White duct tape marked with a wide black sharpie is acceptable for a one race grace period only.
  8. No ballast weight may be mounted to roll cage above rear deck.


  1. Modified and Sportsman: One American Passenger Car sized battery up to 12 volts is permitted. The battery voltage must not measure more than 14.3 volts.
  2. The Battery must be properly secured and must have top and terminals completely covered by rubber.
  3. Battery must be mounted inside the frame rails.
  4. NO step up transformer or any other devise that increases the voltage is allowed.
  5. A battery shut off switch is mandatory. Must be clearly labeled ON/OFF. The switch must be mounted on the left side inner panel (above steering post). The knob must be outside the panel clearly visible and easily accessible. It must be wired to cut off the HOT (positive +) side of battery.


  1. Modified: Only aluminum wheels are permitted. No magnesium, steel, or carbon fiber is permitted. Bleed-off valves are permitted.
  2. Sportsman: One piece steel or aluminum wheels.
  3. Rim width restricted to 14" maximum. This is measured from inside of left bead to inside of right bead on the wheel. Wheel diameter limited to 15" only.
  4. Bead locks are permitted. Any wheel or bead lock that is used must maintain a minimum diameter of 11" hole inside bead lock and wheel. Bead locks may be outside only.
  5. Foam inserts or corrugated plastic (with approved installation) may be permitted when track conditions warrant. No unsafe wheel covers are permitted. Wheel covers that are fastened by way of dzus (or similar type fasteners) are permitted.

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  2. Left rear tire: American Racers (Must be stamped) SD33 (27.5x11) minimum compound.
  3. Right rear tire: American Racers (Must be stamped) SD 38 (29x11) minimum compound.
  4. Left front tire: American Racers (Must be stamped) SD 33 minimum compound.
  5. Right front tire: American Racers (must be stamped) SD 33 minimum compound.
  6. Buffing, cutting, grooving, or sipping will be allowed. No tires chemically altered. Tires will be checked with durometer and sniffer on scales after feature events. Tire markings from the manufacturer can not be altered.



Minimum Weights, including driver- no fuel added:

  1. Under 361 cu. in. flat top pistons on gas 2400 lbs. (3 stage dry sump allowed) *
  2. Under 361 cu. in. ported/domed piston on gas/alcohol 2400 lbs. (3 stage dry sump allowed) *
  3. Over 361 cu. in. 2400 lbs.
  4. Any 4 or 5 stage dry sump add 50lbs*.


  1. Crate Motor - 2350lbs.
  2. Steel Wheels - 2400lbs.
  3. Alum. Wheels - 2450lbs.


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