ARRMA Front Rear Diff Set GP4 5mm 29mm Open Diff 80K Z-ARA311199

Overview

The ARRMA Front/Rear Diff Set GP4 5mm 29mm Open Diff 80K (Z-ARA311199) is a premium differential upgrade designed for serious RC enthusiasts who demand performance and reliability from their RC car UK models. This factory-assembled differential set represents ARRMA's commitment to delivering high-quality drivetrain components that enhance your vehicle's handling characteristics and durability. Whether you're a competitive racer, weekend basher, or someone looking to upgrade their existing RC car setup, this open differential provides the precision engineering needed to keep your ARRMA vehicle performing at its peak.

As an authorised ARRMA dealer in the UK, we recognise that differential upgrades are crucial for maintaining your RC vehicle's performance over time. This particular diff set comes pre-assembled and filled with 80K cSt silicone oil, eliminating the need for complex assembly and allowing you to get back to racing or bashing almost immediately. The GP4 spiral cut design represents ARRMA's advanced engineering, offering improved performance characteristics compared to standard differentials found on many ready to run RC models.

The open differential configuration is traditionally favoured on the rear axle of RC vehicles, allowing the wheels to rotate at different speeds when cornering, which improves traction and handling dynamics. This 5mm 29mm configuration makes it compatible with a range of ARRMA 1/8 scale vehicles, providing a direct upgrade path for owners wanting to enhance their drivetrain performance without requiring extensive modifications to their existing setup.

Key Features

• Factory Assembled and Pre-Filled — This differential arrives completely assembled and filled with 80K cSt silicone oil, saving you valuable time and ensuring proper factory calibration. You won't need to spend hours disassembling, cleaning, and reassembling components; instead, you can install this unit directly into your RC car and get straight to the action.
• Tough Steel Internal Gears — The internal gears are manufactured from durable steel, providing exceptional longevity and reliability in all weather conditions and driving styles. Steel gears resist wear far better than plastic alternatives, meaning your differential will maintain its performance characteristics over extended periods of use, whether you're bashing in muddy terrain or racing on hardpack tracks.
• 43T GP4 Spiral Cut Steel Main Gear — The 43-tooth main gear features a spiral cut design, which is ARRMA's advanced engineering solution for increased durability under extreme loads. The spiral tooth profile distributes stress more evenly across the gear teeth, reducing shock loads and wear compared to straight-cut designs, resulting in longer service life and smoother power delivery to your wheels.
• Strong Composite Differential Case with Integrated Steel Insert — The outer case combines lightweight composite material with strategically placed steel inserts, creating an optimal balance between weight savings and structural rigidity. This hybrid construction approach ensures the diff case can withstand the punishment of aggressive driving while maintaining dimensional accuracy for proper gear meshing.
• Metal Cross Shafts — Unlike plastic alternatives, the metal cross shafts provide increased efficiency and durability. Metal shafts resist bending and twisting under load, maintaining precise gear alignment even during hard acceleration or aggressive cornering, which translates directly to more reliable power delivery and faster lap times.
• Rubber Shielded Bearings — The included rubber shielded bearings offer fast and efficient installation while providing protection against dirt, sand, and moisture ingress. The shielding keeps contaminants away from bearing races without the friction penalty of full seals, making them ideal for both on-road and off-road RC car UK applications.
• Open Differential Design — The open differential configuration allows both wheels to rotate independently, which is essential for maintaining traction during cornering. This traditional differential assembly provides superior handling balance, particularly on the rear axle, making it the preferred choice for racing and aggressive driving styles.

Technical Performance

The ARRMA Front/Rear Diff Set GP4 represents serious engineering designed for 1/8 scale ARRMA vehicles, particularly the KRATON 6S EXB and compatible platforms. The 5mm input shaft and 29mm output configuration specify the exact fitment required for seamless integration into your vehicle's drivetrain. The 80K cSt silicone oil filling provides the perfect viscosity balance for responsive differential action while maintaining adequate film strength between gear teeth and bearing races. This medium-viscosity oil is thick enough to provide proper damping of differential action, preventing sudden torque transfers that could upset handling balance, yet thin enough to allow free rotation when the wheels need independent movement. The spiral cut gear design on the 43T main gear is ARRMA's proprietary advancement, featuring tooth profiles that curve along the gear's axis rather than running parallel to it. This design characteristic increases the contact area between meshing teeth, distributing loads more evenly and reducing stress concentrations that lead to gear damage. The construction utilises tough steel for internal gears, which provide superior wear resistance compared to brass or sintered materials. The composite diff case with integrated steel insert creates a chassis that can flex slightly under extreme loads without permanent deformation, whilst the steel inserts provide locating surfaces that maintain precise gear alignment. Metal cross shafts ensure that the differential spider gears remain perfectly centred, maintaining proper mesh with the ring gear even under the most demanding driving conditions. All components work together to deliver the kind of reliable, consistent performance that separates premium aftermarket parts from budget alternatives.

What's in the Box

• 1 x Factory Assembled Open Front or Rear Diff with GP4 43T Spiral Cut Gear
• 80K cSt Silicone Oil (pre-filled)

Frequently Asked Questions

• What is the difference between an open differential and a locking differential in RC cars? — Open differentials like this ARRMA GP4 unit allow the two wheels on an axle to rotate at different speeds, which is essential for maintaining traction during cornering. This traditional differential design is particularly favoured for rear axle applications because it provides superior handling balance and natural feel. Locking differentials, by contrast, force both wheels to rotate at the same speed, which can cause understeer during turns but provides better traction in straight-line acceleration or when one wheel loses grip. The open differential is the preferred choice for most racing and bashing applications.
• Is this suitable for upgrading my existing ARRMA RC vehicle? — Yes, this Front/Rear Diff Set is designed as a direct upgrade for compatible ARRMA 1/8 scale models, particularly the KRATON 6S EXB. If you own an ARRMA vehicle and want to improve drivetrain performance, durability, and reliability, this factory-assembled unit provides an excellent upgrade path. The pre-assembled, pre-filled design means installation is straightforward, requiring only basic RC car maintenance knowledge.
• Why is the 80K cSt silicone oil viscosity important? — The 80K cSt specification refers to the kinematic viscosity of the silicone oil at 40 degrees Celsius, measured in centistokes. This medium viscosity provides the ideal balance for differential performance: it's thick enough to properly damp differential action and maintain film strength between gear teeth, yet thin enough to allow the differential to operate smoothly when wheels require independent rotation. Oil that is too thin runs off the gears too quickly, whilst oil that is too thick creates excessive friction and sluggish response. The 80K cSt rating is calibrated specifically for this differential's gear ratios and shaft speeds.
• What vehicles is this compatible with? — According to manufacturer specifications, this diff set is compatible with the C-ARA8708V6T1 ARRMA 1/8 KRATON 6S EXB 4X4 RTR Speed Monster Truck. The 5mm 29mm configuration is specific to certain ARRMA platforms, so before purchasing, confirm that your vehicle matches this specification. If you're unsure about compatibility with your particular RC car UK model, our team of experienced RC enthusiasts is available to help verify fitment.
• How often should I service this differential? — Regular servicing intervals depend on your driving style and conditions. For weekend bashers, servicing every 5-10 hours of use is reasonable. For racing applications, more frequent servicing may be beneficial. Because this unit arrives pre-assembled and pre-filled, servicing simply involves draining the old oil, cleaning the components if necessary, and refilling with fresh 80K cSt silicone oil. The factory assembly quality means that once installed, the differential should perform reliably for extended periods with proper maintenance.
• Can I use a different viscosity oil if I want to change the differential's behaviour? — Whilst ARRMA specifies 80K cSt oil for this differential, some experienced RC enthusiasts experiment with different viscosities to fine-tune handling. Thinner oil (like 50K cSt) can make the differential feel more responsive and lively, whilst thicker oil (like 100K cSt or higher) can make it feel more locked up and planted. However, we recommend using the specified 80K cSt oil unless you have experience tuning RC differentials and understand the implications of changing viscosity.

Why Buy from RC Model Shop?

RC Model Shop is a trusted UK RC retailer and authorised dealer for all the brands we stock, including Traxxas, ARRMA, Losi, FTX, Hobbywing, Spektrum and more. Based in Walsall, we have a physical store where customers are welcome to come in, view products and purchase in store. Whether you are a seasoned competitor, a weekend basher, or just discovering the world of RC for the first time, our team of experienced RC enthusiasts is here to help you find the perfect setup and provide ongoing support. Order the ARRMA Front/Rear Diff Set GP4 5mm 29mm Open Diff 80K Z-ARA311199 today with confidence, knowing you are buying from an authorised retailer with genuine products, expert knowledge and a commitment to customer satisfaction. Shop online or visit us in Walsall — we look forward to helping you get the most out of your RC experience.

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