Super X and Super XX Tuning Guide
Super-X and Super-XX are two of Tamiya's rear-motor chassis, sharing the same family lineage as Super-1, Super-II, Super TZ and Super TZ-X on Tamiya's chassis and compatible-parts catalog. They pre-date the midship layouts (MS, MA, ME) that dominate current-release kits, but both remain fully supported chassis, and their wide tread and long wheelbase still make them a distinct, workable platform rather than an inferior stand-in for a modern chassis. This guide covers what differs between the two, where each is structurally weak, and how to gear and mount parts on a rear-motor layout sensibly.
Super-X and Super-XX at a glance
Tamiya's chassis catalog lists both as rear-motor designs sharing an identical 84mm wheelbase and 70mm tread, but differing in length, width, weight and — most notably — ground clearance. Tamiya notes as-built figures vary with the parts installed, so treat these as reference numbers for a representative build, not a fixed spec for every kit.
| Spec | Super-X | Super-XX |
|---|---|---|
| Layout | Rear motor | Rear motor |
| Length | 156mm | 153mm |
| Width | 92mm | 98mm |
| Wheelbase | 84mm | 84mm |
| Tread | 70mm | 70mm |
| Weight | 111.8g | 119g |
| Ground clearance | 5.2mm | 1.9mm |
| Gear ratio(s) | 5:1, 4:1 | 3.5:1 |
For context, official regulations cap overall length at 165mm and width at 105mm, and set a minimum ground clearance of 1mm and minimum ready-to-run weight of 90g — both chassis sit comfortably inside those limits as published, though your finished car must be checked against the current numbers, not assumed from the bare chassis.
From Super-X to Super-XX: what actually changed
Super-XX is described by Tamiya as an evolution of Super-X aimed at improved adaptability and durability, not a ground-up redesign. The two most significant changes are the drop in ground clearance from 5.2mm to 1.9mm and the switch from a two-speed gear option (5:1 and 4:1) to a single 3.5:1 ratio. A lower ride height moves the centre of mass down and can reduce body roll through banked corners, but it eats into the margin above the 1mm regulation floor — debris, a warped chassis, or an uneven joint can ground a Super-XX where a Super-X with 5.2mm of clearance would clear it. Super-XX also brings a revised nose guard that widens front roller settings, and reworked side-stay mounting Tamiya describes as tougher against repeated impacts — useful because rear-motor chassis take wall contact differently from a midship car, covered next.
The rear end is the known weak point
On a rear-motor layout, the gearbox, motor mount and rear axle sit at the back of the chassis — where most of the mass concentrates and where wall contact lands hardest. Repeated impacts there can work the gear cover loose, add play to the rear bearings, and eventually crack the rear chassis tabs the cover clips into: the single most common reason a Super-X or Super-XX that used to run true starts pulling to one side. Inspect the rear chassis and gear cover after every hard hit, not just when something visibly breaks — a hairline crack that still holds under hand pressure often fails mid-run instead. A rear reinforcement plate spreads that load across a wider area and is worth fitting proactively on a technical, wall-heavy layout, the same way a stay or reinforcement plate protects a known stress point on other chassis families.
Motor and gearing for a rear-motor chassis
Rear-motor chassis like Super-X and Super-XX drive the front wheels through a propeller shaft, the same single-shaft arrangement used by standard-range motors — they are not compatible with the double-shaft Mini 4WD PRO motor line built for MS/MA/ME chassis. The full standard motor ladder (Torque-Tuned, Rev-Tuned, Light-Dash through to Hyper-Dash and Power-Dash, where legal) is the correct shopping list; see the motor guide for published RPM, torque and current figures. Since Super-X offers two gear ratios against Super-XX's single 3.5:1, Super-X gives more room to trade top speed for acceleration without changing chassis — pick 5:1 for a technical, corner-heavy layout and 4:1 where straights dominate. For matching a motor's torque curve to a gear ratio rather than choosing either alone, see motor and gear ratio matching. A straight, low-friction drivetrain matters more here than on a midship layout, since the propeller shaft is a second point where misalignment bleeds off power before it reaches the wheels.
Roller and brake mounting on a wide-tread chassis
Both chassis carry a wider tread (70mm) than several modern midship platforms, which changes how a given roller width behaves through a lane change — spacing that feels tight on a narrow chassis can sit close to the legal width ceiling here. Confirm your finished roller-and-body width against the 105mm limit rather than assuming headroom. Super-XX's revised nose guard opens up front roller position options versus Super-X, worth weighing alongside the ground-clearance trade-off above if front-roller tuning matters to your build. For roller-count and spacing decisions themselves, the roller guide covers the general approach; apply it to this chassis's wider tread rather than porting a narrow-chassis setup unchanged.
Where these chassis sit under current rules
Racing Mini 4WD — the category both belong to — is on Tamiya's list of machine types permitted in official races, alongside Fully-Cowled, Aero, Super and Mini 4WD PRO. That does not make every build automatically race-legal: Stock Class rules separately restrict chassis cutting, ban homemade chassis, and require non-Tamiya parts to stay off the car, and BMAX or other organiser classes run their own rulebook, not Tamiya's Stock Class relabelled. Confirm the current official regulations directly and treat on-day technical inspection as final — see the official rules and technical inspection checklist before committing a build to an event.
Frequently asked questions
Are Super-X and Super-XX still legal for official races?
Racing Mini 4WD is on Tamiya's permitted machine-types list, so the chassis itself is not excluded. Legality still depends on the class, the modifications and parts fitted, and the organiser's rules and on-day inspection — always check current regulations rather than assuming permitted status covers every build.
Can I mix parts between Super-X and Super-XX?
Tamiya lists them as separate catalog entries within the rear-motor family. Check a part's listed compatibility before assuming a fit — the width, ground clearance and nose-guard differences above mean not everything interchanges cleanly.
Why is the Super-XX's ground clearance so much lower than the Super-X's?
Published figures put Super-X at 5.2mm and Super-XX at 1.9mm. The lower figure drops the centre of mass and can help stability through banking, but leaves far less margin above the 1mm regulation minimum — a Super-XX build is more sensitive to debris or an uneven joint than a Super-X on the same course.