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Mini 4WD Race Classes: Stock, B-MAX and Open

Monkee Mods

Mini 4WD Race Classes: Stock, B-MAX and Open

“What class am I racing?” is the question that should come before “which motor is fastest.” Mini 4WD does not have one worldwide class tree. Official Tamiya events run on the Official Mini 4WD Race Regulations, with an optional Stock Class that replaces the modification section. Basic-MAX GP publishes its own additional restrictions on top of Tamiya’s rules. Malaysian shop nights often use the word BMAX, Open, or Box Stock for something that may match none of those PDFs exactly. This page maps the names so you stop borrowing legality from the wrong document.

Tamiya Official Regulations (what many shops call Open)

If an event says it follows Tamiya rules and does not name Stock Class, you are in the main envelope: cars must be 4WD, under 105 mm wide, under 70 mm tall, under 165 mm long, at least 1 mm ground clearance, at least 90 g with motor and batteries, tyres 22–35 mm diameter and 8–26 mm wide. Chassis cutting (removing plastic, adding holes) is allowed; homemade chassis are not. Parts must be Tamiya Mini 4WD, R/C Mini 4WD or Dangun Racer. The original part shape must stay identifiable. Motors are a closed list on the Official Regulations page — kit normal, Tuned, Light-Dash, Hyper-Dash 2/3, Power-Dash, Sprint-Dash and the others named there. Batteries at official events are Tamiya-branded R6/AA/UM3. Officials have the last word. Full numbers: rules and tech inspection and the Official Regulations.

Tamiya Stock Class

Stock Class follows the Official Regulations except that section 1-6 Modifications is replaced. The current English Stock Class page marks additions in red on 11 May 2026. The headline change versus the main Official Regulations: you may not cut or shave the chassis. Additional parts are still Tamiya / R/C Mini 4WD / Dangun only. Body work is limited to shaving and cutting obstructions; a body catch is required. You may not cut tyres. You may not heat brake sponges. Rollers may only be used in permitted combinations. HG aluminium setting boards, setting gauges and pinion pullers may not be attached to the car. Plates must be rigid — no wobble, no tapered edges. Only wheels/tyres, rollers, and the internals of mass dampers and sliding dampers may move against the wall. Dash motors are allowed per the Stock Class FAQ. Recheck Stock Class on race week. Comparison with BMAX: Stock Class vs B-MAX.

Basic-MAX GP is an organiser sheet, not a Tamiya class

Basic-MAX GP regulations v5.0 were revised 11 May 2026 and took effect 1 June 2026. They follow Tamiya’s official regulations and replace only the modification section with BMAX’s own list. In v5 that list is very close to Tamiya Stock Class: no chassis cutting, Tamiya-only extra parts, no tyre cutting, no setting boards on the car, plates must be fixed, Dash motors allowed per the FAQ. v5 also publishes numerical inspection fine-print (mass-damper hole wear of 3 mm or more, tyre or roller diameter change of 1 mm or more counts as processing). That sheet governs Basic-MAX GP events. It does not automatically govern a night that happens to be called BMAX in Kuala Lumpur or Penang. Details: BMAX rules 2026. MS Flex, homemade AT bumpers and other community gimmicks are Open-adjacent techniques, not a BMAX default — see MS Flex fundamentals.

Box Stock, Open, and what Malaysian shops usually mean

“Box Stock” is not a Tamiya regulation title. Locally it usually means kit parts, kit motor, maybe a bearing upgrade — or it means whatever that shop printed on the Facebook event. “Open” at a Malaysian meet might mean Tamiya Official (chassis cutting allowed) or it might mean “any Tamiya Grade-Up part, no homemade carbon.” “BMAX” locally often means “no chassis cutting, Tamiya parts only,” which is the Stock/BMAX-GP idea, but battery rules (alkaline vs NiMH) and motor lists still vary. Ask three questions before you build: which PDF, which motor list, which battery rule. How to find a first meet: starting Mini 4WD racing in Malaysia. How to race a tight BMAX-style car without inventing parts: Stock Class and B-MAX setup.

A practical decision order

  1. Read the event name and download the rules the organiser linked, not a blog summary.
  2. If they cite Tamiya Official with no Stock/BMAX addendum, you may cut chassis plastic and you still may not build a homemade chassis.
  3. If they cite Stock Class or Basic-MAX GP v5, do not cut the chassis and do not shave tyres.
  4. If they only say “BMAX” with no PDF, message the organiser. Do not assume v5 or Tamiya Stock.
  5. Confirm motors and batteries in writing. Ultra-Dash in particular is not on Tamiya’s official list.

Frequently asked questions

Is BMAX the same as Stock Class?

Basic-MAX GP v5 currently reads like Tamiya Stock Class with extra millimetre wear limits. They are still two documents. A local BMAX may be a third. Never treat them as one blob.

Does Open Class allow any motor?

Tamiya’s Official Regulations do not. They list permitted motors by name. An organiser’s “open motor” class is a different thing and must say so. See Ultra-Dash.

Can I run one car in every class?

Only if the most restrictive sheet of the day still accepts it. A cut MS Flex that is legal in some Open events will fail Stock and BMAX GP v5 on chassis cutting alone. Build to the tightest class you actually enter, then add Open-only work on a second chassis.

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