Mini 4WD Glossary
Mini 4WD vocabulary comes from two places at once: Tamiya's official regulations, which define exact numbers for weight, dimensions and tyres, and decades of hobbyist shorthand that never appears in any rulebook but gets used at every track. Mixing the two up is where beginners get confused — "BMAX" sounds like an official Tamiya class but isn't, while "MS Flex" sounds like slang but describes a real, documented three-piece chassis. This glossary sorts the terms into the categories they belong to, with numbers sourced from Tamiya's current official pages wherever a number is stated.
Chassis codes and families
Every current kit uses one of two motor layouts. Midship double-shaft chassis — ME, MA and MS — are the only three chassis eligible for Mini 4WD PRO racing, driving all four wheels directly from a centred motor. Everything else below is single-shaft, driving through a separate propeller shaft, split between front-motor and rear-motor layouts.
| Chassis | Layout | What defines it |
|---|---|---|
| ME | Midship, double (PRO) | Rigidity-and-flex balance; current top-tier PRO chassis |
| MA | Midship, double (PRO) | Motor centred for aero balance; six low-friction rollers |
| MS | Midship, double (PRO) | Three-piece nose/centre/tail construction |
| FM-A | Front, single | Aerodynamic, front-weighted balance |
| Super FM | Front, single | Reinforced bumper and cooling ducts |
| FM | Front, single | Long-running platform for undulating tracks |
| VZ | Rear, single | Compact, lightweight, reinforced durability points |
| AR | Rear, single | First rear-motor chassis with six rollers |
| VS | Rear, single | Short wheelbase, hinged gear cover |
| Super-X / -XX / -II / -1 / TZ / TZ-X | Rear, single | Lineage adding stay-mounting and adjustability each generation |
| Zero | Rear, single | Dropped motor/battery position, short wheelbase |
| Type 1–5 | Rear, single | Original lineage the Super series descends from |
For which parts fit which chassis, treat this table as a starting point — see the chassis compatibility list and the full chassis guide before buying option parts.
Official dimensions, weight and tyre limits
These figures come from Tamiya's current race regulations, not community convention, and they apply at technical inspection regardless of how a car is built.
| Measurement | Official limit |
|---|---|
| Maximum width | Under 105mm |
| Maximum height | Under 70mm |
| Maximum length | Under 165mm |
| Minimum ground clearance | At least 1mm |
| Minimum weight (with motor and batteries fitted) | At least 90g |
| Tyre diameter | 22–35mm |
| Tyre width | 8–26mm |
| Straight-section lane width (course spec) | 115mm |
| Course wall height (course spec) | 50mm |
Batteries are restricted to Tamiya-branded AA (R6/UM3) cells; R/C Mini 4WD and TR-1 chassis require alkaline cells specifically, not rechargeables. Tyres must be physically attached and their surface material cannot be altered — a worn tyre is rejectable under the general regulation's 22-35mm diameter limit, while the Stock Class FAQ's "markedly small" discretion applies to rollers. See the official Mini 4WD Race Regulations and the technical inspection checklist — organiser rules and on-day inspection always take precedence over any article, including this one.
Class and modification vocabulary
Stock Class is Tamiya's own official class, built on the general race regulations with extra restrictions: no chassis cutting or shaving beyond what the general rules allow, parts limited to Tamiya Mini 4WD, R/C Mini 4WD and Dangun Racer sources, and a specific "forbidden zone" — between the front and rear shafts/bearings/eyelets, plus the rear halves of the front wheels and front halves of the rear wheels — where only the body and a driver figure may sit. Ball bearings, mixed tyre/wheel sizes and carbon or FRP reinforcement plates are explicitly permitted.
BMAX (Basic-MAX) is different: an organiser-run format, not a Tamiya-published ruleset. Its permitted parts and modification limits are set independently by whichever event runs it, and are not automatically the same as Stock Class — treat each event's own published rules as the authority. See the dedicated Stock Class vs BMAX comparison before assuming one class's rules apply to the other.
General modification vocabulary: "cutting" a chassis means removing material at permitted points only — homemade chassis and non-Tamiya-sourced parts are prohibited outright in both official regulations and Stock Class. Gear modifications are limited to making holes or shaving away material to reduce weight, and installing ball bearings; motors may not be disassembled and reassembled with substituted internals.
Setup and tuning vocabulary
Away from the rulebook, racers use their own shorthand. Chochin ("paper lantern") describes a suspended roller-and-mass setup where a stay hangs loosely on springs or elastic, swinging to absorb landing shock — the opposite of a rigidly bolted stay. Downthrust means angling front rollers slightly downward so the car is pushed toward the track at speed, reducing the chance it launches off a straight. Mass dampers are small weighted parts mounted with play so their inertia absorbs landing shock instead of passing it into the chassis — see the dedicated mass damper guide. MS Flex is specific to the MS chassis's three-piece nose/centre/tail construction: loosening the joining screws lets the sections articulate over bumps instead of behaving as one rigid unit.
Track feature vocabulary
A lane change is the raised bridge section where a car crosses from one lane to another mid-course — a section where roller height and downthrust matter most, since a car that clips the bridge rail loses time or position. A bank or bank-through is a banked curve taken at speed without braking, while a jump section launches the car briefly airborne before landing. Straight sections run at the regulation 115mm lane width between 50mm walls, so roller diameter near the legal tyre width of 8–26mm has a direct effect on wall clearance.
Reading a setup shorthand
Racers write a full configuration as one compact line: chassis, motor, gear ratio, tyre compound, in that order. "MA / Hyper-Dash PRO / 4.2 / hard" describes an MA-chassis car running a Hyper-Dash PRO motor, a 4.2:1 final gear ratio and hard-compound tyres, without a paragraph to say the same thing. For how motor and gear choices pair up on a given course, see motor and gear ratio matching and the motors guide.
Frequently asked questions
Is BMAX just another name for Tamiya's Stock Class?
No. Stock Class is an official Tamiya ruleset published on Tamiya's own regulation pages. BMAX is an organiser-run format with independently published rules, and its permitted parts list is not guaranteed to match Stock Class. Check the specific event's current BMAX regulations rather than assuming Stock Class rules carry over.
Can a PRO chassis motor go in a single-shaft chassis, or vice versa?
No. ME, MA and MS chassis are double-shaft and drive all four wheels directly from a centred motor; every other chassis above is single-shaft, driving through a separate propeller shaft. The two motor families are built for their respective shaft type and are not interchangeable.
Do the dimension and weight numbers in this glossary ever change?
Yes — Tamiya's Stock Class page notes its own dated updates (modification-guideline changes were added as of 11 May 2026), and general regulations are revised over time. Numbers here reflect Tamiya's official regulation pages as reviewed for this article; always confirm current published rules and let on-day technical inspection have the final word.