BMAX Mini 4WD Rules 2026: What You Can Modify
BMAX, in the document that actually exists, is Basic-MAX GP. Version 5.0 of those competition regulations was revised on 11 May 2026 and took effect on 1 June 2026. The sheet does not replace Tamiya’s Official Mini 4WD Race Regulations. It follows them, then swaps out section 1-6 Modifications for its own list. Malaysian shop races that use the word BMAX may or may not be running that PDF. This page explains what v5 actually bans and allows, so you stop treating a YouTube flex build or a Tamiya Stock Class FAQ as a local permission slip.
What v5 is sitting on top of
Dimensions, weight, tyres, the official motor list, Tamiya AA cells at Tamiya events, inspection, and race procedure still come from Tamiya’s Official Regulations unless the organiser says otherwise. Maximum width under 105 mm, height under 70 mm, length under 165 mm, ground clearance at least 1 mm, minimum 90 g including motor and batteries, tyres 22–35 mm by 8–26 mm. BMAX GP v5 does not rewrite that box. It rewrites how much you may alter the car inside it. Always keep the Official Regulations and the v5 page open together. Inspection flow: tech inspection. How BMAX sits next to Stock and Open: race classes.
The modification list that actually changed
Under Basic-MAX GP v5 you may not hollow, cut, or use a homemade chassis. Extra parts are limited to Tamiya Mini 4WD, R/C Mini 4WD and Dangun parts. You may not change the shape of parts other than the body, except countersinking existing holes in FRP/carbon plates and the chassis, and pushing a shaft through a wheel. Body work is limited to lightening and cutting where parts interfere; a body catch is required. Rollers may only be used in the combinations the regulations allow — no adding plastic rings to rollers that do not use them, no swapping rings, no mixing diameters. HG aluminium setting boards, setting gauges and pinion pullers must not be fitted to the car. Drive gears must be used in the permitted combinations; pinions are chassis-specific. Battery terminals are kit or Grade-Up parts installed as the manual shows — no solder, no doubled terminals. No modification that damages the track or flings grease. Batteries only in the specified orientation. Plates must not wobble. A “forbidden zone” between the shafts and inboard of the tyre faces may contain the body (and driver figure) only. Parts that can touch the wall or the running surface must be fixed to the chassis or to a plate that is itself fixed, except wheels/tyres, rollers, and the necessary motion inside mass dampers and sliding dampers.
The v5 fine-print inspectors actually use
Section 3 of v5 gives numerical calls where the main list says “follow the inspector.” Split, unpainted or sticker-less bodies are banned at BMAX GP events. A mass-damper hole whose maximum span is 3 mm or more is treated as processing. A tyre whose diameter has changed by 1 mm or more from wear is treated as processing; the same 1 mm rule applies to roller outer diameter. Body cuts to clear a chassis, plate, mass damper or tyre should stay within 3 mm of the interference — the organiser still judges each case. A body that was lightened and then broken may not race, because the broken edge can injure a marshall or racer. These millimetre rules are BMAX GP’s, not something to invent for a different shop’s BMAX night.
FAQ answers that people get wrong
The v5 Q&A currently says Dash-type motors are allowed, and that parts from a disassembled motor are not. Clear and polycarbonate bodies are allowed; splitting a body is not. You may cut interference to move a body onto a different chassis. Driver figures and wings may be omitted; losing a figure or a wing during a run is not a DQ under that FAQ. Chassis reverse is banned. You may not drill new screw holes; you may countersink, through-drill or open existing holes to 2 mm. Chassis and A-parts in non-kit combinations are allowed. The battery holder may be left off. Ball bearings are allowed. Different tyre and wheel sizes may be mixed; cutting or shaving tyres is not. Worn rollers that have become markedly small are out. You may not swap the bearing inside a bearing roller. FRP/carbon plates may be cement-reinforced and stacked; they may not be fitted loose or edge-tapered. Mass-damper holes may not be enlarged. Heat-treating brake sponge is forbidden as dangerous; cutting brake sponge is allowed. Cementing a gear to a shaft is allowed. Sprues, leftover polycarbonate offcuts and Mini 4WD car-catcher parts used as car parts are not.
What this means for MS Flex, AT bumpers and “gimmicks”
MS Flex, as racers use the phrase, starts with cutting the chassis so the modules can move. v5 item 1 bans chassis cutting. A pivoting homemade AT bumper is a moving wall-contact part that is not a Tamiya sliding damper or mass damper. v5 item 13 requires wall-contact parts to be fixed, with those two families as the motion exceptions. Cementing plates and running Tamiya sliding dampers, mass dampers, carbon plates and Dash motors is the legal upgrade path on this sheet — not a saw. Community names are explained in MS Flex and AT bumpers and sliding dampers so you can recognise them; they are not a BMAX v5 shopping list. Compare also Stock Class vs B-MAX.
Frequently asked questions
Does a Malaysian BMAX night use v5 automatically?
No. Ask the organiser for the PDF. If they have none, you do not have a rule, and an inspector’s call is the whole rule.
Can I run NiMH?
Tamiya official events specify Tamiya-branded AA cells. BMAX GP v5 does not, in the modification section, rewrite the battery brand rule; event operations still follow Tamiya except where the organiser states otherwise. Many Malaysian practice nights allow NiMH. That is an organiser fact, not a v5 slogan.
Is FM-A or VZ “the BMAX chassis”?
v5 does not name a mandatory chassis. FM-A is popular because the front motor helps jump attitude; VZ is popular because it is light and current. Popular is not legal-by-default. Pick a kit you can support, then stay inside the modification list.