TRF421X 1/10 Chassis Assembly Kit

The Tamiya TRF421X is a 1/10 on-road racing chassis kit that builds on the TRF421 with a lower centre of gravity, refined suspension and updates aimed at improving grip. It features an aluminium motor mount, carbon-reinforced suspension parts and adjustable stabilisers.

Key features

• 1/10 on-road competition chassis kit
• 4WD belt-driven TRF421 platform
• Lower-positioned aluminium motor mount for a lower centre of gravity and more stable cornering
• 2.0 mm thick aluminium lower chassis deck for improved balance and weight distribution
• Choice of one-piece or two-piece upper deck braces, developed for improved chassis flex
• Suspension arms in carbon-reinforced nylon for improved stability
• New shock mounts with revised mounting positions
• Front drivetrain/spool cups updated (steel instead of aluminium)
• Rear differential updated (steel instead of aluminium)
• New upper arm mounts for improved steering response
• Updated knuckle arms with revised hole positions for Ackermann tuning (front) and rear grip tuning (rear)
• Adjustable stabilisers: 1.2 mm (x2) or 1.3 mm (x1)
• Improved left-to-right weight balance

Overview

The TRF421X is a further development of Tamiya’s TRF421 on-road racing platform, aimed at drivers who race on high-grip circuits. The updates are based on feedback from competitive racers and focus on finer tuning and more consistent performance.

The most noticeable change is the new aluminium motor mount, which positions the motor 1.04 mm lower than on the standard TRF421. This lowers the centre of gravity and helps deliver more stable cornering and improved grip. The new 2.0 mm aluminium chassis deck supports this lower motor position while also contributing to chassis flex characteristics and weight distribution.

The suspension has been revised as well. The suspension arms are now moulded in carbon-reinforced nylon (instead of glass-reinforced), which helps maintain the right amount of flex and stability, especially on high-grip or carpet tracks. The shock mounts feature new mounting points moved 1.0 mm inwards, refining the handling balance.

The drivetrain has also been updated. Up front you get a new double cardan driveshaft design with bearings to reduce friction, while the rear uses lightweight aluminium universal shafts with bearings. Both the front spool cups and the rear differential have been updated with steel components instead of aluminium for improved durability and consistency.

Steering geometry is improved with new knuckle arms that offer revised hole positions for Ackermann tuning at the front and rear grip optimisation at the rear. The upper arm mounts are 1 mm narrower for a sharper cornering response.

Stabilisers are adjustable, with 1.2 mm and 1.3 mm options depending on track conditions and driving style. Added receiver and battery weights help fine-tune left-to-right balance.

This is a chassis kit, so you build it yourself. Tamiya supplies the chassis and suspension components, but you’ll need to add your own motor, servo, ESC, wheels/tyres, body and battery.

Specifications

• Scale: 1/10
• Type: chassis kit
• Drivetrain: 4WD, belt-driven
• Shocks: TRF aluminium oil-filled
• Suspension: independent double wishbone
• Differential setup: oil-filled gear differential (rear) / direct coupler (front)
• Use: on-road competition
• Receiver weight: 20 g
• Battery weight: 30 g

Still needed

• 2-channel radio system
• Low-profile steering servo
• ESC
• 540-size motor
• Wheels and tyres
• 190 mm touring car or sports car body
• 7.4V battery with compatible charger

Conclusion

Looking for a refined 1/10 4WD on-road racing chassis for high-grip tracks? The Tamiya TRF421X combines a lower centre of gravity, carbon-reinforced suspension parts and adjustable stabilisers — a strong base for competitive racing.