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RC Gearing 101: Ramping Acceleration or Top End Speed

By Josh •  Updated: 03/14/21 •  13 min read
RC Cars & Trucks

There is nothing in this world that is more fun than having your RC car blasting through obstacles and around tracks at speeds you could barely think of. The fine-tuning of an RC car is one of the most pleasurable hobbies you might find yourself in, with many enthusiasts barely hitting any track at all, instead of laboring away for hours to get the best from their cars.

The art of RC car tuning starts with the gear ratio and knowing what you want from the engine when you need it so lets dig deeper into how rc gearing works. 

There are two types of RC car enthusiasts, those that want uncontrolled speed from the get-go, and those that want top-end speed to match a real car. For the best acceleration in your RC car, making it a monster through turns you will need a larger pinion gear, translating speed from the engine faster to the wheels.

RC cars that can drive in more open spaces and have tougher hills to climb benefit greatly from smaller pinion gears, but larger spur gears. 

Understanding the intricacies of RC car gearing can make a great difference in how well your car is performing. Many times, enthusiasts try every combination under the sun before giving up and starting to make their gear systems.

However, for the casual racer, it can be extremely intimidating first entering the world of RC driving, and learning that the gears are the most important part of the car.

How Does RC Gearing Work?

RC gearing is not nearly as complicated as a real car’s gearing system and understanding the basic principle only takes a few minutes. The pinion gear is connected directly to the engine or electric motor, this gear then links with the spur gear.

As the motor turns, the pinion gear turns, and that in turn turns the spur gear, the spur gear is connected to the driveshaft of the car.

This simple but effective system ensures that there is almost no energy lost from the turning of the motor to the turning of the wheels. Depending on how the system has been created it may mean that there is virtually no loss of speed to the wheels either.

In some systems you can gain more speed to the wheels than the engine is producing, however, you will sacrifice a lot by doing this.

It is the balance of the gears, the engine, and the drive shaft that is what makes the RC car go and accelerate at blistering speeds.

Many RC owners work for years trying to create the best ratio of gears to fulfill what they need, the large impressive 4-wheel drive cars that can climb mountains will have gear systems unrecognizable from those that simply have to drag race in a straight line. 

What are the most important parts of RC gearing?

Apart from the obvious motor and drivetrain, two parts of the gearbox will change with each car, and these are the most important parts. Understanding what these two parts are will greatly change how you plan your RC car, and improve the way you may add things onto the car. 

Many people forget that the wheels on an RC car count in how much torque is needed and knowing how the complete gear system works will mean that you never have so little that you cannot move.

Creating a good gear ratio system in the RC car that you love, means that you can be assured that it is not the weakest on the track, or that it would get stuck when the going gets tough. 

Direct power from the pinion

The pinion gear is connected directly to the engine or electric motor and is by far the most important gear in the system. This gear is almost always made from either cast iron, steel, or aluminum, depending on the strength of your motor. This is the gear that is solely responsible for the engine translating its movement to the rest of the car. 

Fuel-powered cars will also have a friction clutch in this gear, that kicks in when the engine reaches a certain acceleration. This is what gives petrol-powered RC cars their massive acceleration as the engines are already outputting a large amount of power when the gear engages.

For electric motors, this gear is always engaged and can translate the direct power produced by the engine into the movement of the wheels. 

Conversion through the spur gear

There are two locations where the spur gear can be located on an RC car and each of which has its benefits. The size of the spur gear about the pinion gear is what will decide how much speed, or how much torque you have on the wheels of your car.

This is why you need to learn which is better, what systems will work best for what kinds of tracks. 

For the standard locations of a spur gear, it will be directly mounted onto the driveshaft between the two rear tires. This means that the speed and energy go to the two rear wheels, making the RC car a rear-wheel-drive car, usually having the engine or motor parallel to the rear driveshaft.

The second and more complicated, way that the spur gear can be mounted is on a central driveshaft in the car. This created an all-wheel-drive car that can climb near-vertical walls without much trouble. 

Which pinion gear is faster? 

The smaller the pinion gear is to the spur gear the faster the car can accelerate, with larger pinion gears or just slightly larger than the spur gear making RC cars that can go at seemingly impossible speeds.

These are the cars that you may see go from standstill to well to their top speed in a flash, as the car accelerates at a blinding speed.

This is because of the turning ratio of the pinion gear towards the spur gear, with each turn of the pinion translating to less than one or fewer turns of the spur gears.

As the pinion gear turns faster and faster, the spur gear translates it into pure acceleration, but a lower top speed. However, while there are some engines and motors that can easily handle at this ratio, it will rarely be used in such a configuration by enthusiasts planning to go to the extremes

Usually, this is the standard ratio that you will find in RC cars and even the best RC cars will have a ratio that is the same. However, when going into the world of enthusiast RC cars the need for speed, torque, and acceleration becomes evident.

While low gears are great for a few minutes of fun, a lot more work is needed when you want to have a car that can go over mountains at top speed.

What does a bigger spur gear do?

The spur gear is by far the most complex part of the gear systems and the debate about which one is the best, what material is the best, or even what teeth ratio is efficient has been going on for too long to remember.

Many hobbyists love to tinker and play with their gears, and once the bug for RC cars has bitten you the very first thing you may change is the spur gear.

This is the gear most responsible for the torque power of your overall car, easily increasing the base torque of the motor to something almost impossible to believe.

While larger pinion gears will mean your car has a higher top speed, it will mean that your RC car can be stopped by even slight sands.

Having the ratio right will mean that you are hitting the perfect peak torque for your RC car, while it is going at the absolute top speed it can go. 

Most of the time people will fit smaller spur gears when they are going to be doing races where they know they may have to race across longer straights in the race.

While they may not be perfect for races with a lot of turns or rougher terrain, these ratios are also famous for putting a lot more strain on the motor, and the battery if you are using an electric motor.

It is best to use these for straights where you want to reach a top speed rather than blast out of a corner. 

Which gear has the best acceleration?

For acceleration, the best gear ratio will always be in favor of spur gears being larger than the standard. This is because the gears should be balanced and ready to go with the pinion gear not losing too much energy to the spur gear, allowing the wheels to turn almost as fast as the motor. Turning raw RPMs into wheel motion.

You will still need to ensure that there is some space for a top speed in the gear system as not having will mean you die out on any straights, which is why the pinion gear should not be so large that there is no possible turnover happening.

Preferably this gear ratio lies somewhere at 1:2 or 2.4 depending on how large your wheels are. 

This will allow the gear system to turn extremely fast and the engine to effortlessly move the car at near top speed from the start. This is possible because there is another reduction of energy happening when the spur gear is moving the driveshaft.

The driveshaft is in the middle of the spur gear, where it will be turning the fastest, the driveshaft then turns the wheels. Your wheels need to be in the right relation to your gears to ensure that the power is not lost when trying to turn them. 

What gear ratio is better for high speeds?

Top speed is the trickiest part of any RC car as it is affected by a multitude of things, not least of which is the ratio between the pinion gear and the spur gear.

Most standard RC cars will have a 1:1.6 or 1.8 relationship between the two, as this allows for a good amount of acceleration from the start but allow for far more top speed.

These are the cars that will not be able to go for as long as a lot of energy is needed to make the car move. However, once the car is moving in a straight line it will be able to go at a pace that most other RCs won’t be able to match.

Usually, racers will adjust their cars to have a better high speed once they know the race track they are using has almost no obstacles and has a lot of straight lines. These are races that are usually done on tarmac or cement, in the middle of a mall, city, or parking lot.

However, some prefer to do this with their cars because it offers a lot better balance and control, the slower acceleration means that the car becomes forgiving.

Allowing you to comfortably go full throttle on the gas without the car blasting off in the direction it was facing at that moment. Ironically enough, if you are still learning how to control and predict where your car will go, this gear ratio will be the safest bet. 

How to read the teeth on a pinion or a spur gear?

This is the easiest and most complex part of changing the gears that you will have to go through. Both gears will have a set of numbers on them when you first look at them, saving you from having to count each tooth by hand, and inevitably getting lost.

On spur gears this will usually look something like 83T, showing that it has 83 teeth, the pinion gear will have a similar number on it.

However, you will also need to calculate the ratio between the two gears to know how well they are working together, or even if they can work together.

To get this ratio you will need to divide the number of teeth on the spur gear by the number of teeth that are on the pinion gear, the result giving you the ratio. 

You can use this ratio to see how strong your current gear setup is, or when going to look for stronger gear systems you can see which ones will be compatible with your engine or motor.

Changing and getting the right gear ratio is the most important part of getting your car going faster than you could ever imagine. 

Why would you need to change the gears?

There are many reasons that you may want to change the gear system in your car, usually closely followed by you changing the gears to fit a new racetrack.

You will inevitably join some type of race with your RC car and getting it to be perfectly capable will mean that you can easily enjoy having your car race ahead of the rest.

There are generally four reasons that you or other enthusiasts may want to change the gear ratio system in their cars. Usually, these are done a few days before a race, or even just done when they know they will be in unknown terrain.

While changing the gears is a simple process, it is not something that can be done on the fly and in most cars requires quite a bit of disassembling to accomplish. 

Final Thoughts on How RC Gearing Works

RC gearing feels daunting when you start, but after one or two weekends of tinkering, you will find that the mountain was only a molehill.

Getting the best RC gear ratio means that you are using a gear system that is both strong, fast, and accelerates well. All three of which are on contradictory points of a triangle. 

Whatever you do, do not use gears meant for low torque engines, RC motors and engines are some of the strongest in the small world. 

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Josh

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