Changing your car's gear ratio is an easy way to change the performance of your RC car. So it is very important to know how to set up a good gear ratio! Indeed, incorrect configuration can cause overheating issues and performance issues. You can also increase speed at the expense of torque, or vice versa. You can change the transmission ratio of your car by modifying the engine pinion or the crown .
What is a pinion and a crown?
What is a gable?
The pinion is the tiny gear that fits into the motor and is usually made of metal. The most common metals are aluminum, steel and titanium. The ring gear is the slightly larger gear on the transmission side which is driven by the motor pinion . It is often made of plastic and sometimes composite materials or even Kevlar. When the engine turns, it drives the engine pinion which in turn drives the ring gear which is connected to the car's transmission shaft. Changing the sprocket will have a more pronounced effect on performance, so if you want to make more subtle changes, change the ring gear. Switch both for maximum effect or finer adjustments .
What are the characteristics of the sprockets?
The characteristics of the pinions and crowns are the diameter of the axle, the number of teeth and the pitch. Typically, the number of teeth (expressed in T) and pitch (expressed in P or DP) is engraved on the sprocket, but some manufacturers omit this information. The pitch refers to the size of the teeth . There are a few common sizes we use in RC, such as 32 steps (32P), 48 steps (48P), and 64 steps (64P). There is also a metric variation on the pitch: 1 Mоd , 0.8 Mоd and 0.6 Mоd . It is important to know that 32 steps and 0.8 Mod are the same thing and can be used interchangeably. The higher the pitch, the smaller the teeth.
Why change the gears on my RC?
Although changing the wheel diameter can affect your car's final drive ratio, the most common way to affect this setting is to change the pinion and ring gear . In fact, increasing or decreasing the number of teeth on one of the gears affects the number of times the pinion must turn to turn the ring gear a full revolution (hence the name transmission ratio ).
An electric car uses an onboard battery , so there is always a limited amount of energy available to use during a race. The transmission ratio must therefore be optimized to ensure that the battery is not completely exhausted before the car has crossed the finish line or you have finished your race but also to avoid overheating the engine or even improve his behavior.
How does gear ratio affect performance?
For each pair of pinion/crown gear in an RC car , there is a gear ratio. It corresponds to the number of teeth of a gear divided by the number of teeth of the corresponding gear. Gear ratios are important because they allow us to better control speed and torque .
RPM and torque are inversely proportional: when one increases, the other must decrease. Optimal output speed can be achieved by adjusting the transmission ratio. Another point to note, it is much easier to extract power from a high speed (high RPM) brushless motor than from a more basic motor. All this is made possible by changing the transmission ratio.
High gear ratio, low revs
- Small pinion, large crown
- High torque, low revs
- Fast and lively acceleration, lower maximum speed.
- Less voltage and heat on the motor and drive
- Longer run time on battery
Your car will accelerate very quickly, but the top speed it reaches won't be as high. The car will be easier to control at high speeds, but the high torque and instant power can make it feel aggressive. High-end variators allow you to program a softening of the throttle or a reduction of punch. This can make the car much easier to drive, resulting in a smoother ride and faster lap times .
With low RPM, you will benefit from longer run times and lower operating temperatures for the variator and motor. This is due to the fact that the engine is under less stress. However, be careful not to undervitaminate too much as this can also cause overheating.
Low gear ratio, high rpm
- Large pinion, small crown
- Low torque, high rpm
- Slower acceleration, higher maximum speed
- No more stress and temperature rise on the motor and variator
- Shorter operating time on battery
The car does not accelerate as fast but reaches a higher top speed . With less torque , the engine has to work more while the car accelerates. This additional stress on the engine results in higher operating temperatures . This will reduce the operating time per battery charge compared to low RPM. A gear ratio that is too low should be avoided, or measures taken to ensure that the motor and variator do not heat up too much. Installing an additional fan aimed at the engine and cutting a few ventilation holes in the bodywork should help.
Finding the right balance
In theory, a small winding track with many curves or tight turns will be suitable for low rpm, while high rpm will be better for a large open track with long straights . However, a high RPM with smoother acceleration may be easier to drive in certain situations while a low RPM car operating on a high-grip track may be difficult for beginners to control.
On low grip tracks , or in wet/icy conditions, a high gear ratio (and therefore a low revving car) will give you more traction out of corners, so this setup is worth having. tried even on small technical routes. Smooth driving will help you achieve consistent lap times, so try to find the right gear for the type of track you want to ride on.
Choose the Right Gear Ratio for Your Engine
How to calculate the transmission ratio?
We have seen that the relationship between the pinion and the crown is very important to be able to influence the performance of your RC car . To calculate this ratio, simply divide the number of teeth on the crown by the number of teeth on the pinion . If your car has a 20 tooth (20T) sprocket and a 100 tooth (100T) ring gear, your ratio is 5:1 (100 ÷ 20 = 5), which means the sprocket should make five turns to turn the crown one turn.
For example, let's say your friend's car runs well, has good acceleration and top speed, and the battery and motor aren't overworked. You have the same car, same engine, and equal capacity battery, so you want to use the same gear ratio. It has a 20T sprocket and a 100T ring gear for a 5:1 ratio. If your sprocket is a 125T, which sprocket should you use? Divide the teeth of the spur gear by 5 (since you are aiming for a 5:1 ratio) which gives us 125 ÷ 5 = 25. You should use a 25T pinion. Even if you have bigger gears than your friend, the ratio is still the same: 5:1. Although you can select any transmission ratio you want, you need to take into account the engine being used. Your RC car's manual should give recommendations on gear ratios.
Which gears should I choose based on my engine?
A high rotation motor (13.5t, 17.5t, etc.) will have more torque but a lower top speed. Therefore, a higher revving engine will require a combination with a larger pinion and smaller ring gear to be able to use all that torque at low rpm. Low rotation motors such as 5.5t or 8.5t will generally need a combination with a smaller pinion and larger ring gear.
If you find that your car seems to be lacking power, you may have a bad transmission ratio. Check your RC car's instruction manual to find out the recommended range of pinions and ring gears for your motor .
What is the role of tire size on the transmission ratio?
Two elements influence the distance traveled by an RC car during a rotation of the motor. These two elements are the transmission ratio and the diameter of the tires . A simple mathematical formula can be used to gather this information, allowing millimeters per revolution to be accurately calculated.
If you take two identical cars with identical gear ratios and put small diameter tires on one and large diameter tires on the other, the vehicle with the larger tires will go further with each rotation of the tires. wheels. To truly understand your car's total drive ratio , you need to consider the size of the drive wheels (or more precisely, their circumference).
To measure the distance traveled by the tire in one revolution, calculate the circumference of your tire by multiplying pi (3.14) by the diameter of the tire. For example: 3.14 x 5 inches = 15.7 inches. If we divide this number by the 5:1 gear ratio, we get this result: 15.7 inches ÷ 5 = 3.14 inches. This means the car advances 1.31 inches for each revolution of the gear.
What is “not”?
The “pitch” of a gear refers to the size of its teeth and more specifically, the distance between a point on one tooth and the corresponding point on the next tooth. The higher the pitch, the smaller the teeth. The pitch of your car's gears has no effect on the transmission ratio: a 100T ring gear/20T pinion combination always has a 5:1 ratio, whether you use 32, 48, or 64 pitch gears. However, certain gear pitches are better suited to certain applications.
32 pitch sprockets
This big step is no longer found much on 1/10 electric vehicles , but we still find it on thermal cars , Monster Trucks and Short Course 4x4s . In fact, they use 32 pitch gears to cope with the high power exerted on their transmissions.
48 pitch sprockets
This intermediate pitch saves you from choosing between 32-pitch gears (durable, but limited in options) or 64-pitch gears (lots of options, but the smaller teeth are more fragile). Standard 48-pitch off-road sprockets provide the perfect balance of ratio options and durability.
64 pitch sprockets
It is the step of choice for riders who ride on the track mainly because of the large number of gears available and the extra-smooth mesh of the very fine teeth. Since track cars don't have to endure jumps and bumps, 64-pitch sprockets hold up well.
