HBX 901a Brushless 1/12 pinion gear speed upgrade

The HBX 901a 1/12 brushless truck as reviewed here is a brushless 1/12 scale desert buggy and one of my favourite RC cars of 2021. It was light yet very durable with a very efficient power system and drive train. Short gearing ensured very lengthy battery life and ensured motor and ESC temps remained extremely low with the preference of strong acceleration over top speed. In this article I'll show you how to install a larger 14t pinion gear and talk about the performance improvements.

In my original review I mentioned that the motor mount for this car had preset motor holes that should allow the fitment of a 14t pinion and recommended the Surpass Hobby M0.6 13-17t pack. I can now confirm that these do fit as expected - see the images and steps below to do this yourself - it is very easy and takes around 5-10 minutes.

14t Pinion Install Guide

Click on any image to embiggen

Remove the 4 screws that hold the motor down and the 3 screws that hold the gearbox shroud down

Removing the gearbox shroud shows you how the stock 12t pinion meshes with the metal spur gear

The motor mount, motor and heatsink assembly comes out as a unit (motor easily unplugs from ESC)

The heatsink is stuck on with a conductive glue - I had to pry it off (removed cleanly with no damage)

You need to take the heatsink off before you can remove and reorient the motor. Keep the red circular heat shield between motor and mount

Heatsink off and motor out. There are no markings on the motor but looks like a regular Surpass 2845 in 3800kv. I had to pry the pinion off as the grub screw was rounded

Here is the pack of Surpass Hobby pinion gears I recommend (13t - 17 pack). Shown alongside stock 12t pinion.

14t pinion gear is on and done up loosely.

Motor is reoriented in the 14t position with m2.5 screws. Ensure the red heat shield goes between motor and mount

Screw the motor down with the 4 mount screws in tighten the pinion grub screw so that the teeth align cleanly

Gear shroud screwed back on.

In the boot and ready to test!!!

Performance Review

First up the mesh with this pinion is perfect and the gears continue to be extremely quiet on this car.

Improvements
When I reviewed this car with the stock 12t pinion gear I managed a top speed of 39km/h. Not super quick but the strong acceleration and outstanding battery life more than made up for it although it did feel a little slow in large open areas. With the larger 14t pinion gear as installed above I was able to increase the top speed to 45 km/h which certainly feels a little faster, especially in big open spaces. I can't really feel that I've lost anything in acceleration which suggest to me that at least with my driving that it was probably a bit under geared before.

Downsides
​Going up in pinion size does bring a few downsides as expected: Battery life is down from around 20 minutes to maybe around 17 minutes. Additionally the car has gone from having a barely lukewarm motor and ESC at the end of a battery to having a warm motor and kinda hot ESC however this was in really tough conditions - 26 degrees C ambient temp today and thrashing it full throttle on loose gravel and on grass; something of a torture test. Below is my initial reaction when I finished the first pack on this car:

Summary - should I do this for my car?

In short yes, I definitely recommend this mod. The downsides I mentioned above are not really that bad because the gearing was originally so conservative meaning it had massive battery life and the coolest motor and ESC I've ever felt. This means giving a little of this away is barely an inconvenience. On the plus side no one really ever says no to wanting a little more speed, especially when the acceleration is not really compromised. The beauty is that if it is not for you then you can easily revert back to stock and you have more knowledge about your car for very little money spend. All in all a mod for the already excellent HBX 901a brushless 1/12 truck that I heartily recommend.

Part I used:

Surpass hobby M0.6 pinion gear set from Banggood (set 1: 13t, 14t, 15t, 16t, 17t)

HBX 901A RTR 1/12 2.4G 4WD 45km/h Brushless RC Cars Fast Off-Road LED Light Truck Models Toys Update! Use code BGR901A to get 10% off the regular price

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