Many motorists, choosing a new car or thinking about tuning transmission, are faced with technical characteristics that at first glance seem to be dry numbers. One of the key parameters that determine the behavior of the car on the road is gear-rate. It is from this value that it directly depends on how fast the car can accelerate, what maximum speed it can develop and how effectively the engine torque will be used.
There is a common misconception that large numbers in performance always mean higher speed, but in mechanics everything works exactly the opposite. The higher the gear ratio, the more torque is transferred to the wheels, but the lower the maximum speed of rotation of these wheels. This is a fundamental law of physics that cannot be circumvented, but can be managed to achieve specific goals.
Understanding this dependency is critical not only for engineers, but for every driver who wants to extend the life of their vehicle. Incorrect selection of the main pair or gearbox can turn a frisky city hatchback into a sluggish cart or, conversely, make a heavy SUV unsuitable for off-road due to the lack of traction.
Physical meaning of the transfer number
To understand the nuances of the transmission, you need to return to the basics of mechanics. Transfer ratio This is the ratio of the number of teeth of the driven gear to the number of teeth of the leading gear in any transfer. Simply put, it is an indicator of how many times the input shaft (connected to the engine) must turn for the output shaft (associated with the wheels) to make one full rotation.
If we are talking about the main pair in the rear axle gearbox, a high value, for example 4.44, means that the driveshaft needs to make more than four revolutions for the wheels to turn once. This creates a huge gain in strength, but a loss in rotational speed. Conversely, a low number, say 3.0, allows the wheels to rotate faster at the same engine speeds, but the traction force is reduced.
It is important to distinguish between “long” and “short” transmission. In automotive terminology, “short” gears have a high gear ratio and provide fast acceleration, while “long” gears (low) are focused on economical driving on the track. Engineers are always looking for balance, as it is impossible to get the maximum thrust and the maximum speed at the same time in one gear.
⚠️ Attention: Installing the main pair with an excessively high gear ratio on a civilian car will lead to over-consumption of fuel on the road and a decrease in engine life due to work in the high-speed zone.
In addition, it should be borne in mind that the transmission is not only a transmission. In the calculation of the final effort, and gear ratios The main pair, and even the diameter of the wheels. Changing any of these parameters shifts the balance between acceleration dynamics and maximum speed.
Impact on acceleration dynamics and traction characteristics
The main question that worries drivers: how will the behavior of the car change if you increase the gear ratio? The answer is clear: the car will become "bad" at the bottom. Increasing the number of main pairs is the easiest way to add torque to the machine without interfering with the engine or installing a turbocharging.
With a high gear ratio, the engine gains speed faster, which reduces the acceleration time from place to 100 km / h. The car becomes more responsive to pressing the gas pedal, there are failures when overtaking in the city stream. This is especially true for cars with a small engine capacity, which lacks its own power for a confident start.
But the medal has a downside. By increasing traction, you automatically reduce the range of speeds available in each gear. This means that you will have to switch to the next step more often. If the standard box allows you to accelerate in the third gear to 120 km / h, then with the "shortened" main pair, the limit can shift to the mark of 90-100 km / h.
For racing tracks or drag racing, high gear ratios are the standard. Every split second is important there, and the top speed is often limited by the length of the track. In such circumstances torque It is more important than the ability to develop 200 km / h.
- 🚀 Increased gear ratio improves acceleration dynamics at low and medium speeds.
- ⚙️ The engine quickly reaches peak power, which improves the responsiveness of the accelerator.
- 🔄 The speed threshold at which it is necessary to switch to the next gear is reduced.
- 📉 The load on the clutch and transmission elements increases at sharp starts.
Relationship with fuel consumption and environmental friendliness
The question of efficiency is faced by every car owner, and here the gear ratio plays a decisive role. There is a direct relationship: the higher the gear ratio, the more engine speeds are required to maintain a certain speed. And more revolutions is more fuel burned per unit of time.
In an urban cycle where acceleration and braking are constant, a higher gear ratio can even reduce consumption slightly, since the engine will less often operate in incomplete combustion modes when trying to start from low rpm. However, on the track, when driving at a constant speed, the “short” main pair turns the car into a voracious car.
Modern environmental regulations force engineers to make transmissions more "longer". This allows you to reduce CO2 emissions and meet strict consumption limits. New cars often seem less fast at the start compared to models 20 years ago, but they are much more economical.
To reduce fuel consumption on the road, try to move at the maximum possible transfer at the minimum stable engine speeds, avoiding "twisting".
And we must not forget that aerodynamic resistance. At high speeds, the main load is not taken on by the mass of the car, but by air resistance. If the gear ratio is too high, the engine will roar at high revs, trying to overcome this barrier, which will lead to a sharp increase in fuel consumption.
| Type of gear ratio | Expenditure in the city | Expenditure on the track | Dynamics of acceleration | Salon noise |
|---|---|---|---|---|
| High (Short) | Medium/Low | High-pitched | Great. | High-pitched |
| Low (Long) | High (at start) | Low. | Medium/Weak | Low. |
| Optimal (factory) | Balanced | Balanced | Medium | Medium. |
| Extreme (Sport) | High-pitched | Very tall. | Maximum | Very tall. |
Role of transmission in the cross-country SUVs
For SUV owners, the question “the higher the gear ratio, the higher the gear ratio.” has a completely different answer. Here speed is not important, the ability to turn the wheels in dirt, snow or on a steep climb is critical. That is why in the design of all-wheel drive cars there are transfer boxes with a lowering row.
Low Range short-term increases the total transmission ratio several times. This allows the wheels to rotate slowly but with tremendous effort. Without this mechanism, even a powerful engine would not be able to pull out a stuck car, since the torque would simply not be enough to overcome the resistance of the ground.
In addition, for heavy SUVs, regular main pairs in bridges are often changed to more "tractional". This compensates for the installation of wheels of increased diameter. If you put large wheels without changing the gear ratio, the car will become sluggish, and the load on the engine will increase to critical values.
☑️ Off-road preparation of the SUV
The mechanisms are not designed for long-term operation under load at high speeds, and such a mode can lead to rapid destruction of gears and bearings.
- 🏔️ High gear ratio in the transfer is critical to overcome steep climbs.
- 🚜 Allows you to use the winch and other attachments with maximum efficiency.
- 🛞 Compensates for the loss of traction when installing large diameter wheels.
- 🚫 It is strictly forbidden to use a lowered row on hard coatings with good adhesion.
Technical risks and resource of aggregates
Mechanical interference with the transmission is always a risk. An increase in the gear ratio of the main pair creates an increased load on all elements that transmit torque. The axles, clutch, and even the crankshaft of the engine begin to work in a more stressful mode.
This is especially true for cars with automatic transmissions. Hydrotransformer may not cope with increased loads, which will lead to overheating of the oil and accelerated wear of frictions. Manufacturers rarely provide a margin of safety for such modifications, so the automatic transmission resource can be reduced by several times.
⚠️ Warning: Before replacing the main pair, be sure to check the state of the clutch and the squeezed bearing. The sharp increase in torque on wheels often causes a slip or rupture of the clutch disc on older cars.
It is also worth considering that changing gear ratios can knock down the readings of the speedometer and odometer. Electronics will calculate the speed based on the standard parameters, which will lead to incorrect data on the dashboard and possible problems when passing a technical inspection or communicating with the traffic police.
How to adjust the speedometer readings?
To correct the readings after changing the size of the wheels or the main pair, you need to reprogram the transmission control unit (TCU) or use an external speedometer corrector that makes a correction factor in the speed signal.
Poorly executed replacement of the gears of the main pair can lead to the appearance of a howl in the bridge. Pairs of gears rub against each other at the factory, and their replacement requires high qualification of the master and the use of special devices to adjust the contact spot.
When a replacement of the main pair is needed
There are a number of situations where changing the gear ratio is not a whim, but a necessity. First of all, it is a deep tuning engine. If you have increased the power of the engine, but left the standard transmission, you will not be able to effectively use the increased potential, especially at the start.
The second case is a change in the purpose of the car. Turning a truck into a motorhome or preparing a jeep for expeditions requires a shift in balance towards thrust. The third option is recovery after a breakdown, when the original spare part cannot be found, and you have to choose an analogue with similar characteristics.
Accurate calculations must be made when making a decision on replacement. It is necessary to take into account not only the desired dynamics, but also the power reserve of the engine, the condition of the gearbox and operating conditions. Blindly following advice from the internet can make the car unsuitable for everyday driving.
Replacing the main pair is a compromise: you get an improvement in one parameter (thrust or speed), but inevitably lose in another (consumption or top speed).
It is also worth mentioning CVTs, which are devoid of fixed gear ratios. They can change the ratio continuously, simulating both short and long gears depending on the position of the gas pedal. This makes them versatile, but less reliable at high loads compared to classical mechanics.
Frequently Asked Questions (FAQ)
How does a change in gear ratio affect the maximum speed?
The higher the gear ratio, the lower the maximum speed of the car in each gear. The engine quickly reaches the maximum speeds, not allowing the car to accelerate to the previous values.
Can I increase the gear ratio on a car with automatic transmission?
Technically it is possible, but it is not recommended without serious refinement of the cooling system and reflashing of the control unit. Automatic boxes are very sensitive to changing loads and can quickly fail.
Why do SUVs use different gear ratios in bridges?
Using different numbers in the front and rear axle is impossible with all-wheel drive connected, as this will break the transfer case. However, on some older models with the front-end switched off, this was allowed in rear-wheel drive mode.
How to calculate a new gear ratio when installing large wheels?
It is necessary to divide the diameter of the new wheel by the diameter of the regular and multiply the obtained coefficient by the standard gear ratio of the main pair. This will help to return the car to the factory dynamics.
Does the wear of the clutch affect the perception of the gear ratio?
Yes, worn-out clutch can slip, creating the illusion of a lack of traction that drivers often mistakenly try to compensate for by changing the transmission settings, although the problem is solved by replacing the disc.