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Gear size refers to the geometric characteristics of gears calculated through core parameters such as module, number of teeth, and pressure angle, which essentially reflect the physical specifications and meshing capability of gears. As a fundamental parameter, the module (m) is defined as the ratio of the pitch to the circumference π (m = p/π), directly determining the tooth height and tooth thickness. For example, the tooth height of a gear with a module of 0.5 is 1.125 mm (2.25 × 0.5), while that of a gear with a module of 1.0 doubles to 2.25 mm. Gear size calculation covers key data such as reference circle diameter (d = mz) and addendum circle diameter (da = d + 2m). For instance, the reference circle diameter of a gear with 16 teeth and a module of 0.4 is 6.4 mm. It should be noted that gears that mesh with each other must have the same module; otherwise, normal transmission cannot be achieved. The standardized design of gear sizes (such as the module series specified in JIS B 1701) ensures manufacturing compatibility, while the modified gear technology can adjust the center distance to meet non-standard requirements. These parameters collectively affect the torque transmission efficiency and mechanical strength of gears, and are core considerations in the design of transmission systems such as automotive gearboxes.

The gear ratios from 1st to 7th gear in an automobile transmission refer to the rotational speed ratio between the input shaft and the output shaft at each gear position. Their numerical design directly affects the vehicle's power output and fuel efficiency. Taking manual transmissions as an example, the 1st gear ratio is usually between 3.0:1 and 5.0:1, achieving high torque output through a large gear ratio, which is suitable for starting or climbing. As the gear position increases, the gear ratio gradually decreases. For instance, the 5th gear ratio is approximately 0.7:1 to 1.0:1, while the 6th or 7th gear (more common in high-performance or energy-efficient models) may further drop to around 0.6:1 to reduce the engine speed during high-speed cruising. The gear ratio distribution logic of automatic transmissions is similar, but the specific values vary due to differences in brand technologies. For example, the 1st gear ratio of some 7-speed dual-clutch transmissions is about 4.7:1, and the 7th gear ratio may be 0.6:1. It should be noted that the actual gear ratio is comprehensively influenced by the vehicle's positioning, engine characteristics, and final drive ratio. For example, the low gear ratios of commercial vehicles may be as high as 6:1 or more to meet heavy-load requirements, while the overdrive gear is designed to improve fuel economy through a gear ratio of less than 1. It is recommended to consult the technical manual of the specific vehicle model to obtain accurate data.

D4 is a gear identifier for automatic transmission vehicles, indicating that the transmission can automatically shift between gears 1 and 4, making it suitable for most daily driving scenarios. During normal driving, the system automatically selects the appropriate gear based on vehicle speed, engine RPM, and road conditions. For instance, it starts in first gear and progressively shifts up to fourth gear as speed increases to optimize power delivery and fuel efficiency. Common automatic transmission gear positions include P (Park), R (Reverse), N (Neutral), and D (Drive). Within the Drive mode, sub-modes like D3 restrict the transmission to third gear maximum, which is ideal for hill climbing or overtaking, while D4 is better suited for steady-state driving conditions such as highway cruising. In certain vehicle models, D4 may also refer to engine technology specifications—Toyota's D4-series engines, for example, employ direct fuel injection—though this interpretation depends on specific model context. While proper use of D4 enhances driving smoothness, switching to lower gears is recommended in challenging conditions (e.g., steep inclines or heavy traffic) to maintain better vehicle control.

The numbers 1, 2, and 3 on a car's gear shift typically appear in manual transmission vehicles or the manual mode of automatic transmissions, each representing different gear ratios and power output ranges. Gear 1 is the starting gear, providing maximum torque, suitable for moving the vehicle from a standstill or climbing steep slopes. Gear 2 is used for low-speed driving or gentle inclines, serving as a transition between Gear 1 and Gear 3. Gear 3 is suitable for medium-speed driving, such as urban roads or situations with speeds between 40 to 60 kilometers per hour. These numbered gears adjust the relationship between engine speed and wheel speed to achieve more efficient power delivery and fuel economy. For automatic transmission vehicles with manual mode (e.g., M or S mode), drivers can manually select gears 1 through 3 to handle specific road conditions, such as using lower gears during long descents to employ engine braking and reduce brake system strain. Proper understanding and use of these numbered gears can improve driving safety while optimizing vehicle performance.

There are three main methods for calculating the gear ratio. The first is based on the number of gear teeth, with the formula: gear ratio = number of teeth of the driven gear ÷ number of teeth of the driving gear. For example, if the driving gear has 20 teeth and the driven gear has 40 teeth, the gear ratio is 2:1, meaning that for every full rotation of the driving gear, the driven gear rotates half a turn. The second method uses the inverse relationship of rotational speeds, with the formula: i = rotational speed of the driving gear ÷ rotational speed of the driven gear = number of teeth of the driven gear ÷ number of teeth of the driving gear. If the driving gear rotates at 3000 rpm and the driven gear at 1500 rpm, the gear ratio is also 2:1. The third method combines torque and power parameters, with the formula: transmission ratio = operating torque ÷ (9550 ÷ motor power) × motor input speed ÷ service factor, which requires integrating motor performance and operating condition data. Gear ratio design directly affects vehicle performance. A large gear ratio (e.g., 1st gear) is suitable for climbing or heavy loads, as it increases torque but sacrifices speed. A small gear ratio (e.g., 5th gear) is beneficial for high-speed cruising and reducing fuel consumption. Modern transmissions optimize shift smoothness and fuel efficiency through multi-speed dense gear ratios (e.g., 8-speed transmissions). Additionally, electronic gear ratio technology can improve control precision by adjusting the pulse equivalent—for instance, optimizing the pulse equivalent from 2.44 μm/pulse to 1 μm/pulse can significantly enhance machining accuracy. A reasonable gear ratio configuration needs to balance power output, fuel economy, and driving comfort.

In manual transmission vehicles, low gears refer to those with smaller numbers, so 1st gear is a low gear, while 4th gear is a higher gear. 1st gear is mainly used for starting the vehicle or climbing steep hills, where the engine can provide maximum torque but the vehicle speed is low; as the gear increases (such as 4th gear), the vehicle speed increases while the torque decreases, which is suitable for smooth driving. The low gear in automatic transmission models is usually marked as L (Low) or 1, and its function is similar to the 1st gear in manual transmissions, applicable to scenarios requiring strong traction, such as going uphill or towing heavy loads. Correctly understanding the differences between gears helps optimize the driving experience. For example, using low gears in congested areas with frequent starts and stops can reduce clutch wear, while switching to higher gears during high-speed cruising can improve fuel economy. It should be noted that the L gear in some automatic transmission models may correspond to the transmission being limited to operating within the range of 1st to 2nd gears, and the specific details should be confirmed in the vehicle manual.

Gears 1 to 5 of a manual transmission car correspond to different speed ranges and driving scenarios respectively. Gear 1 is used for starting from a standstill or climbing steep slopes (0-15 km/h), providing high torque to overcome resistance. Gear 2 is suitable for low-speed driving (10-25 km/h), ideal for congested roads or complex road conditions. Gear 3 is the acceleration gear (20-45 km/h), balancing power output and smoothness. Gear 4 is for medium-high speed cruising (40-60 km/h), offering better fuel economy. Gear 5 is specifically designed for high-speed driving (above 60 km/h), which can reduce engine load and improve fuel efficiency. When shifting gears, attention should be paid to matching vehicle speed and engine speed. After starting in Gear 1, gears should be shifted up sequentially, avoiding skipping gears. Gear 5 is usually engaged when the vehicle speed exceeds 50 km/h and can be maintained during high-speed cruising (80-100 km/h) to optimize fuel consumption. Proper use of each gear can extend the lifespan of the transmission while ensuring driving safety and economy. For example, when going downhill, gears can be shifted down to 3 or 4 to utilize engine braking. Manual transmission operation requires coordination with the clutch, and movements should be gentle and accurate, avoiding prolonged half-engagement of the clutch or incorrect gear shifting.

Car gears refer to the mechanical devices in the transmission that adjust the engine's output speed and torque through different gear combinations, with the core principle being to change the gear ratio to adapt to different driving needs. Manual transmissions disconnect power via the clutch, and the driver manually selects gear engagement—for example, 1st gear uses a large gear ratio (such as 3:1) to amplify torque for easy starting and climbing, while 5th gear with a small gear ratio (such as 0.8:1) improves cruising efficiency. Automatic transmissions rely on torque converters and planetary gear sets, with the ECU automatically switching gears based on vehicle speed and accelerator pedal depth, offering functions like D gear (regular driving) and S gear (sport mode with delayed upshifting). Special gears include P gear, which ensures parking safety by mechanically locking the wheels; R gear, which reverses the output shaft to enable reversing; and B gear, which uses engine braking to reduce brake load when going downhill. Current mainstream transmission technologies also include the fast shifting of dual-clutch transmissions and the smoothness of CVT (Continuously Variable Transmission). When choosing, one needs to consider driving scenarios and fuel economy—for instance, automatic transmissions are more suitable for urban commuting, while manual transmissions are preferable for those pursuing a sense of control. Regular replacement of transmission fluid (recommended every 60,000 kilometers) is crucial for maintaining the lubrication and heat dissipation of the gear set.

In the current Malaysian market, models equipped with a 9-speed transmission include the diesel version of the JAC T9 pickup truck. This model features a precisely calibrated 9-speed transmission system, delivering smoother gear shifts and optimized fuel efficiency. Priced at RM119,888, it comes with an 8-year unlimited-mileage engine warranty. The 9-speed transmission technology significantly improves power output linearity through its multi-gear design, making it particularly suitable for pickup trucks that need to balance payload capacity and long-distance driving demands. Additionally, high-strength alloy materials and intelligent structural design minimize mechanical wear. As for the Xpeng X9, though this pure electric MPV doesn't specify transmission gear counts, its single-motor front-drive system combined with dual-chamber air suspension similarly prioritizes ride smoothness - though electric vehicles typically employ single-speed transmissions. For users with explicit multi-gear transmission requirements, fuel-powered models are recommended, while also suggesting they monitor transmission technical specifications released through official brand channels.

A gear ratio of 3.73 means that the rotational speed ratio between the driving gear and the driven gear in a transmission or differential is 1:3.73, i.e., for every one revolution of the driving gear, the driven gear rotates 3.73 revolutions. This value is calculated through the reciprocal relationship of the number of gear teeth or the pitch circle diameter, reflecting the conversion efficiency between rotational speed and torque during power transmission. A higher gear ratio (such as 3.73) implies a greater torque multiplication effect, which is suitable for vehicles requiring strong starting or climbing performance. However, the engine speed will be relatively high during high-speed cruising, which may affect fuel economy. In contrast, a lower gear ratio is more conducive to quietness and fuel efficiency during high-speed driving. Under Malaysia's mixed road conditions with numerous ramps and urban areas, such settings are commonly found in pickup trucks or SUV models to balance low-speed traction and high-speed performance. The optimization of the gear ratio also needs to consider engine characteristics and transmission gear distribution to ensure linear power output and driving comfort.