Prepare your Tamiya Cars. This racing season will be epic!

xStock Rules and Regulations 2024


Rules and Regulations


Update on Inspection

  • Upon inspection of car, no adjustment may be made to the car.  Any adjustment made requires the racer to resubmit the car for inspection again.

Golden Rule:  All Tamiya Cars and parts only.

The most important rule once again, ALL TAMIYA only!

  1. ***ALL TAMIYA ONLY***. **This will be STRICTLY enforced through inspection before every race. If it is determined that a car contains "non-Tamiya" parts, the car and racer will NOT RACE that heat and will be considered as having lost the heat. While it is acceptable to paint parts, if the inspector’s are unable to identify that it is an original Tamiya part, the inspector may conclude that it is NOT A TAMIYA PART. The inspector's decision is final.
  2. One car per racer only. We register the racer, not the car.  A racer can only register ONE CAR per category.  We may allow more than one car in certain races. 
  3. Alkaline (1.5V) or Rechargeable batteries (1.2V) are allowed. Be advised that there may not be enough outlets in the venue. We will not be able to provide additional outlets. Please bring enough batteries.  

The general rule is that no custom modification to parts are allowed.  Use upgrade parts as is.  More details are listed in the guide below.


The above takes precedence over the following rules.

Usable Machine Types

Only Mini 4WD REV, Mini 4WD PRO, Racing Mini 4WD, Super Mini 4WD, Fully-Cowled Mini 4WD, Aero Mini 4WD, Mighty Mini 4WD, R/C Mini 4WD, and Truckin' Mini 4WD machines are permitted. Further restrictions on machine types may be possible depending on the race event or race class.

Machine Assembly

All machines must be four-wheel drive. Modifications that result in rear-wheel or front-wheel drive are prohibited.  Bodies must meet the requirements below:

  • Only plastic bodies are allowed. No Poly Carbonate bodies.  Bodies should have stickers applied.
  • Bodies must be fixed front AND rear with Tamiya body catches.
  • Bodies may not be split into separate pieces.
  • Any combination of body and chassis is permitted.
  • Wing parts may be omitted.
  • Home-made bodies are prohibited.

All machines must go through car inspection and machines that do not pass inspection cannot participate in the race. As a general rule, machines must be assembled by the racer. Some exceptions may be applied. Please ask Race Officials.

Machine Measuring System

All machines must have a 4WD setup and will be subject to the same measuring system as shown below.

  • Maximum Car Width: Under 105mm
  • Overall Car Height: Under 70mm
  • Overall Car Length: Under 165mm
  • Minimum Ground Clearance: At least 1mm
  • Minimum Car Weight (including batteries and motor): At least 90g
  • Front and Rear Tires: Diameter: 22-35mm, Width: 8-26mm (Note that tires must be attached.)
    • Tires and wheels must meet the requirements below:
      • Tires and wheels must be of the same size. Example: low-profile tires cannot be used on large-diameter wheels.
  • Rollers: No maximum number of rollers.
  • Mass Dampers: The installation positions of rotating mass dampers are no longer limited.

When adding parts to the bumpers, side guards or the chassis, please note the zone restrictions below.

Definition of Bumpers - For MS chassis, the bumper is the section on the Front or Rear Unit not including the Bumperless Unit. On other chassis, bumpers are the sections forward and rearward of the front and rear gearboxes respectively.
Definition of Side Guards - Parts that extend from the sides of the chassis between the front and rear tires.

  • Parts which extend around the outside of the wheels to completely frame the chassis are not allowed.
  • Parts attached to the front bumper cannot extend past the line of the front axle.
  • Parts attached to the rear bumper cannot extend past the line of the rear axle.
  • Parts attached to the side guards must remain within the lines shown: (back edge of Front Tire & front edge of Rear Tire)
  • Chassis: Extension parts which are attached to the chassis itself are subject to the same zone restrictions as similar parts attached to the bumpers or side guards.

There are no rules for parts which pass above or within the outside edges of the tires.
There are no rules for mounting rollers, etc. to the body as long as they are above the level of the wheel axles. If they extend below this line, they will be subject to the same limits as parts which are attached to side guards.


Machines may use the kit-included normal motor, Rev-Tuned Motor, Torque-Tuned Motor, Atomic-Tuned Motor, Sprint-Dash Motor, Power-Dash Motor, Hyper-Dash 2 Motor, Light-Dash Motor, Hyper-Dash 3 Motor, Rev-Tuned 2 Motor, Torque-Tuned 2 Motor and Atomic-Tuned 2 Motor. Mini 4WD PRO machines may use Rev-Tuned 2 Motor Pro, Atomic Tuned Motor Pro, Torque-Tuned 2 Motor Pro, Light Dash Motor Pro, Hyper Dash Motor Pro and Mach-Dash Motor Pro.  All other motors are prohibited.

  • Depending on the race event, we may modify the allowed motors, but it will be clearly communicated. 
  • Disassembling the motor to change the number of coils and other such illegal modifications are prohibited.
  • If there are indications that the motor cap has been detached, it will be judged as being illegally modified.   


Alkaline (1.5V) or Rechargeable batteries (1.2V) are allowed. Batteries must be installed in the manner instructed for the chassis.  Chassis layout may not be reversed.

Be advised that there may not be enough outlets in the venue. We will not be able to provide additional outlets Please bring enough batteries.  Please note that some events may have different rules regarding which types or brands of batteries can be used.


No modification to any chassis, body, motor, tire, wheel, battery, and parts can be accepted. 


  • Only plastic bodies are allowed. No polycarbonate bodies.  No Home made bodies.
  • Bodies must be fixed front AND rear with Tamiya body catches.
  • Bodies may not be split into separate pieces.
  • Any combination of body and chassis is permitted.
  • Wing parts may be omitted.
  • Body Cutouts:  Sections that clash with chassis, plates or mass dampers may be cut off.
    • Please leave a gap of 3mm at most to the obstruction (where necessary, race officials’ rulings will be final)
  • Canopy sections may be cut away or removed if an animal figure is used.
    • Animal figures themselves may be modified.
    • Animal figures must be securely cemented or attached with double-sided tape.
  • Only sections instructed in that model’s manual may be cut away; likewise, mesh may only be added if instructed in the manual.
  • Cars will be disqualified if their animal figure falls out, or if cutaway sections on the body, wing etc. break.
  • Body Cutouts that are excessive and exceed the rule above are prohibited.  

Chassis - Only the following modifications are permitted:

  • Screw holes may be countersunk. Countersinking is allowed for all screw holes.
  • Cutting or trimming of chassis is prohibited.

Mass Dampers - Modifications to mass dampers must conform with the regulations below:

  • Mass damper weights may not be modified.
  • Mass dampers may only move up and down on a fixed screw. If a hanging damper falls from underneath its plate, etc. the car will be disqualified.
  • Ball connector mass damper arm sections may not straddle wheel shafts. If a ball connector mass damper falls off during a race, the car will be disqualified.


Tires & Wheels - Tires and wheels must conform with the regulations below:

  • Tires may not be modified.
  • The only modification permitted to wheels is extending holes for wheel shafts through the wheels fully.
  • Tires may be affixed to wheels (double-sided tape, cement, etc. are permitted).
  • No modification to the tire size/characteristics are allowed.
  • Tires and wheels must be of the same size.


Rollers - Rollers must conform with the regulations below:

  • Rollers may not be modified. Anodized rollers and modify rollers are not allowed (CNC)
  • Rollers that have worn down to a sharp edge are not permitted.
  • Roller numbers and sizes are governed by the official Tamiya regulations.


Plates - Plates made from FRP, carbon and duralumin, etc. must conform with the regulations below:

  • Countersunk screws and tapered edges are the only permitted modifications.
  • Countersinking is allowed for all screw holes. 
  • Plates must be properly and tightly fixed. They may not move. Tamiya sliding dampers are permitted.
  • FRP and carbon plates may be reinforced using CA cement.


Other Parts - Use of other parts must conform with the regulations below:

  • Approval is required for modified parts prior to their use.
    • Metal parts such as screws and shafts may not be modified.
  • Only official combinations of chassis and A parts are permitted.
    • Example: Super-1 chassis battery cover may not be used on the Super-II chassis.
  • Sprue and polycarbonate body offcuts may not be used to modify setup.
  • Parts made from Mini 4WD catchers may not be used.
  • Battery cover must be used.
  • Only kit-included battery terminals or Grade-Up Part battery terminals, installed according to the instruction manuals, may be used. Soldering or double-plated terminals are prohibited.
  • Only official Tamiya brake parts may be used.
    • Brake sponge may be cut to size.
  • Brake parts may not be modified via heating.
    • This is enacted as some stores and users may not have access to equipment.
  • Parts removed from the inside of a motor may not be used.
  • Any sections of screw or shaft that protrude significantly must be covered with rubber tubing, a stabilizer ball, etc.



  • No lantern dampers allowed.
  • Touhoku dampers, Catcher dampers, and others are prohibited. Only Ball connector damper used in their intended position are allowed.


Any other questions, please ask the inspectors to settle before the race. 


Race Courses 

For courses which satisfy the below specifications and are sanctioned by Tamiya, times recorded during races will be officially recognized. All times recorded on original courses that do not meet these requirements will be considered unofficial.

  • Individual Lane Width: 115mm (measured on a straight section)
  • Course Wall Height: 50mm (measured from road surface)
  • Adjusting the height and lane width of lane change sections, bank turn sections, etc. for smoother racing operations is permitted.

For Competitions at Official Race Courses 

  • The start of the race will be indicated by a signal from a Tamiya race official or a starting signal system. Racers will switch on their cars, hold them in the air with one hand, and drop them vertically into their assigned lane at the start signal. Throwing or pushing the car forward is prohibited.
  • A racer will immediately retire from a race if their car leaves the track, flips over, jumps into another lane, or if their car's body detaches during the race.  The race marshals will have the final discretion whether to pick up a car that is no longer upright on the track.   
  • If race officials determine that a racer's car is blocking the progress of faster machines, the racer will be required to retire.
  • A car's race is completed when it reaches the finish line.
  • Qualifying and Final positions are determined by either the race finishing order or Time Attack time.

Car Inspection

  • All racers must have their car inspected by race officials before the race. If any part of the car is determined to be against race regulations, the racer will be considered to have lost the corresponding heat.  If the racer has not reached his/her maximum loses, the racer may make the required modifications and participate in the racer’s next heat. 
  • From the time the car passes the car inspection to when the race begins, the car's settings must not be changed and no modifications can be made.
  • In addition to the pre-race car inspection, other car inspections may occur at any time during the race day at the race official's discretion. If the car is found to be in violation of the race regulations at any of these inspections, the racer's race results up to that point will be disqualified and the racer must make necessary changes in order to participate in subsequent races.
  • If a machine does not pass car inspection, and cannot be made race-legal, the participant can still take part in the Qualifying rounds for their own benefit, but their times and standings will not be recorded.


If any of the following situations occur, race officials will, at their discretion, have absolute authority to disqualify any racer. Please take care to remember the common manners for a Mini 4WD race to avoid any problems.

  • A racer's car is determined to have modifications that will cause physical harm to other racers, other cars, or the race track.
  • A racer's car is determined to have modifications that are designed to deliberately obstruct other cars.
  • A racer deliberately puts grease or other substances onto the track to affect track surface conditions.
  • A racer is determined to have modified their car after it had passed the car inspection including, but not limited to, removing O-ring from rollers.
  • A racer is determined to have deliberately touched the track or cars to impede other racers' race progress.
  • A racer does not follow the instructions of race officials or otherwise impedes the operations of the race track.
  • A racer has a false start, or is determined to have thrown or pushed their cars forward at the start of a race.
  • A racer is determined to have acted against the spirit of fair play or caused distress to other participants.

Race Operations

  1. Participants may raise objections to the race officials. However, these objections must be made before the next race begins.
  2. Race officials reserve the right to announce the use of special regulations at any time during the race.

Participant Restrictions

  1. Please be aware that some races have age limitations, so it may be that some participants cannot take part in certain classes or races.

Except for endurance races, it is against regulations to have more than 2 racers using the same car.


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