Class Rules
Box Stock Class Rules
CHASSIS
Allowed: Kyosho MR03S, MR03S2, MR03 RTR, MR04 RWD, Associated SR27 (RWD only)
Not Allowed: Shaving chassis or removing sections for weight reduction
Chassis must be raced as manufactured from the box
WHEELBASE
Only allowed wheelbases: RWD 90mm, 94mm, 98mm, and 102mm
MOTOR & ESC BOARD
Kyosho MZ9P, MZ9E Motor from RWD RTR
Permitted modifications:
Changing motor wires with same or maximum (20) gauge wire
Removing safety switch
Motor must be run as manufactured with no other manipulations or modifications
Not Permitted: EVO Board or other upgraded board
GEAR RATIO
6T - 9T Pinion (included with RTR kits)
Stock Kyosho Gear Diff only
WHEELS
All brand plastic and aluminum 1/28 scale production wheels allowed
Size limitations:
Maximum front-wheel width: 8.5mm (not including outer flange/disk)
Maximum rear-wheel width: 11mm (not including outer flange/disk)
Maximum wheel diameter: 20mm
Minimum wheel diameter: 19mm
Wheels must be original designs made for 1/28 scale cars
Wheel and tire must fit inside the body
TIRES
Maximum tire diameter (mounted): 25.5mm
Front tires must be 8.5mm and rear tires 11mm
Not Allowed:
Traction compound on tire or race surface
Tire warmers
Homemade tires
Foam tires
Silicon tires
Urethane tires
Ethyl Carbonate tires
Tire inserts
Tires may be cleaned with 70% alcohol solution or water
Using illegal tire cleaner will result in penalties
Direct tire-related questions to the driver's meeting or race director
BATTERIES
Cars must be powered by 4 AAA batteries
Allowed types: Alkaline, Ni-MH, or Ni-Cd
An additional battery is allowed only for transponder connection
ELECTRONICS & TRANSMITTER
Stock Radio from RTR Kit
WBMRC Exception – Aftermarket Radios Permitted
Only Kyosho original items included in the RTR box are allowed
No modifications to radio permitted
BODY
Any manufactured molded hard shell that fits the allowed wheelbase
All parts must be original for that body
Limited wheel and ground clearance modifications allowed
Size limitations:
Maximum body length: 180mm
Maximum width: 83mm
Not Allowed:
Shaving/thinning body material for weight reduction
Lexan roofs, windows, and wings
Headlight requirements:
Original headlight covers must be installed
Headlight buckets may be removed/omitted
Lost headlight covers may be replaced with decal/tape
Taillights and covers may be removed/omitted
Small body parts (mirrors, canards, exhausts, front splitters) may be omitted to prevent racing damage
Wings: Standard rear wings for corresponding hard-shell body may be used with no height limit
Custom aftermarket plastic wings must meet 45mm height limit from ground
OPTION PARTS
Allowed from any manufacturer: bearings, wheel nuts, springs, and T-Plates
Only original Kyosho front and rear suspension parts may be used
No added weight via tungsten, brass, or other materials
MODIFICATIONS
King pin flip allowed, lower pin must be shortened to no damage track
WBMRC Exeption - 0 Degree Metal Knuckles permitted
Lipo 2500 Modified CLASS REGULATIONS
WHEELBASE
Allowed models: Kyosho MR03S, MR03S2, & MR03 RWD, Jomurema, GL Racing GLR, GLR-GT, GL-GTR, MRC MRC01, PN PNR2.5W, PNR3.0, RTRC RTA, Atomic MRZ, MRX, MRV, RX28/SE G1, G2 and G3, NEXX Skyline, Specter, MWX R.1, G-Force Lightning, XBility XB 1, AE RC28
WBMRC Exeption - Publicly Available 3D Printed Chassis Are Permitted
WHEELBASE
Only allowed wheelbases: 98mm and 102mm
MOTOR
Any 1/28th scale manufacturer 2500Kv sensored motor
Maximum can diameter: 15mm
Maximum Kv: 2800
No aftermarket rotors allowed
Motors must not be tampered with or modified
GEAR RATIO
Any 1/28th scale manufacturer pinion and spur allowed
Tooth count must be distinguishable by markings or color for easy tech
All gears must be Pre-Event teched and painted
Standard ratio: 12T Pinion / 53T Spur (unless specified for track conditions by event)
WHEELS
All brand plastic and aluminum 1/28 scale production wheels allowed
Size limitations:
Maximum front-wheel width: 8.5mm (not including outer flange/disk)
Maximum rear-wheel width: 11mm (not including outer flange/disk)
Maximum wheel diameter: 20mm
Minimum wheel diameter: 19mm
Wheels must be original designs made for 1/28 scale cars
Wheel and tire must fit inside the body
TIRES
Maximum tire diameter (mounted): 25.5mm
Front tires must be 8.5mm and rear tires 11mm wide
Tire warmers are allowed
Tires may be cleaned with 70% alcohol solution or water
Not Allowed:
Traction compound on tire or race surface
Homemade tires
Foam tires
Silicon tires
Urethane tires
Ethyl Carbamate tires
Tire inserts
Using illegal tire cleaner will result in penalties
BATTERIES
2-cell LiPo or 2 one-cells paralleled (maximum 8.40 volts)
Max battery dimensions 45 x 24.0 x 13.0mm
Battery must be identifiable with original sticker from 1/28th MiniZ manufacturer
Maximum 500 mAh
An additional battery is allowed only for transponder connection
ESC / RECEIVER
Any manufacturer 1/28 ESC and Receiver allowed
ESC must not have any timing, turbo or boost activated and have a visual Blinking LED. (Blinky Mode) LED. (Blinky Mode)
Not Allowed:
Receivers with built-in Gyro
Separate Gyros
BODY
Any manufactured molded hard shell that fits the allowed wheelbase
WBMRC Exception - Lexan and Hard Bodies will be combined in this class to maximize the class size. Lexan Bodies are allowed too.
All parts must be original for that body
Limited wheel and ground clearance modifications allowed
Lexan roofs, windows, and wings are allowed
Size limitations:
Maximum body length: 180mm
Maximum width: 83mm
Minimum Weight: 24 grams
Headlight requirements: Original headlight covers must be installed
Headlight buckets may be removed/omitted
Lost headlight covers may be replaced with decal/tape
Taillights and covers may be removed/omitted
Small body parts (mirrors, canards, exhausts, front splitters) may be omitted to prevent racing damage
Wings: Standard rear wings for corresponding hard-shell body may be used with no height limit
Custom aftermarket plastic wings must meet 45mm height limit from ground
OPTIONAL PARTS
Any aftermarket 1/28 scale publicly available production or 3D printed parts allowed
Adding weight via tungsten putty, stick weight, or cut hobby brass is allowed
Not Allowed:
Prototype parts
Public availability requirements:
Parts must be publicly announced via social media or website
Parts must be available for purchase nationally 45 days prior to race
3D print files must be shared with the public 30 days before event start
WEIGHT
Full car minimum weight: 160 grams (race ready)
Any questions concerning class rules should be addressed at the driver's meeting or with the race director.
WBMRC has adopted the 28SRA Rules as of September 2026. This allows us to be more uniform across classes and be prepared to participate in the larger Regional and National races that have adopted the 28SRA rules as well. We do have a couple of Club Specific Exceptions and they are noted as such.