What is the minimum speed for fourth gear?

[MacMaria]

For manual transmission vehicles, the minimum speed for fourth gear is 40km/h. Below is a related introduction about vehicle gears: Speed aspects: First gear corresponds to a speed of 0-5km/h, second gear to 5-20km/h, third gear to 20-40km/h, fourth gear to 40-60km/h, and fifth gear to 60-100km/h. Shifting timing: The general shifting timing for most vehicles is when the engine reaches 2000r/min, and should not exceed 2500r/min. For some high-displacement, high-power engines, shifting can occur around 3000r/min.

[McAubrey]

Back when I drove a manual transmission car, I specifically tested this issue. There's no fixed minimum speed for 4th gear - it really depends on the specific vehicle model and engine condition. With my 1.6L car, 4th gear could maintain stability around 35-40 km/h, any slower and it would shake like sitting on a massage chair. The engine would stall easily if RPM dropped below 1000, especially noticeable when going uphill. Newer cars nowadays might handle it better, with turbocharged engines providing greater low-speed torque that could potentially maintain at 30 km/h. But honestly, I wouldn't recommend driving like this - long-term high-gear low-speed driving harms the engine and wastes fuel.

[StephenRose]

Having worked in an auto repair shop for twenty years, I've frequently encountered drivers asking this question. To be honest, the minimum speed in fourth gear primarily depends on three factors: engine displacement, transmission gear ratio, and load conditions. For an average family car with no load, the engine will struggle below 40 km/h in fourth gear, and if the RPM drops below 1200, it'll start shaking noticeably. However, with a larger displacement engine above 3.0L, you might barely maintain stability at 35 km/h. Once, a customer's pickup truck was carrying half a ton of cargo, and at 45 km/h in fourth gear, it was shaking like a leaf. Remember, the tachometer is more reliable than the speedometer—keeping the RPM above 1500 is the safest bet.

[AlessandraLynn]

After studying the transmission data of dozens of cars, the minimum speed in fourth gear is determined by both the gear ratio and engine characteristics. For example, a typical 5MT transmission usually has a fourth gear ratio ranging from 0.9 to 1.1. Combined with the engine idle speed (around 800 rpm), the theoretical vehicle speed is approximately 30 km/h. However, in actual driving, torque margin must be reserved; otherwise, the engine may stall with slight throttle input. Through practical testing, it was found that most cars shift smoothest into fourth gear within the 40-50 km/h range, while speeds below 35 km/h generally result in lugging. There are noticeable differences between brands, with German cars typically exhibiting higher tolerance than Japanese cars.

[MaverickAnn]

As a beginner, I also struggled with this issue. Later, I learned that the minimum speed in fourth gear is all about feel: when the speed drops below 40 km/h, the throttle response becomes noticeably sluggish, and a slight vibration through the steering wheel serves as a warning signal. If you don't downshift at this point, the engine will emit a muffled whine, and after a few more seconds, the entire car starts to shudder. Once, on a mountain road, I forgot to downshift and stubbornly held fourth gear at 30 km/h, only for the engine to stall completely. Later, my mentor taught me to watch the tachometer—shift to third gear immediately if the RPM drops below 1500. This trick saved me a lot on tow truck fees. Now, driving an automatic, I actually miss this kind of mechanical interaction.

[SanLouis]

Compared the differences between manual and automatic transmissions: the minimum speed for 4th gear in manual transmissions is mostly in the 35-40 km/h range, but automatic transmission models don't have a strictly corresponding concept of 4th gear. When driving a friend's 6AT model, I noticed the transmission automatically downshifted to 3rd gear at 32 km/h. Different drivetrain types also have an effect - front-wheel drive vehicles are more prone to lugging vibrations than rear-wheel drive ones. Many modern cars now have gear shift indicators that illuminate when speed falls below preset thresholds. The safest approach is to consult the owner's manual - mine clearly states 4th gear should be maintained above 45 km/h. Extreme testing is meaningless; it's those pretend-knowledgeable veteran drivers who actually damage vehicles.