1. Why the forks rise twice as high as the hydraulic cylinder
Forklifts have two forks attached to the front mast. These forks move up and down along the mast using the force of a hydraulic cylinder.[3] Besides the cylinder, parts like lift chains help raise the load platform, while a separate tilt cylinder angles the mast forward or backward.[1]
The chain system is interesting. According to UK forklift training materials, the chain is wrapped around a pulley on the cylinder side and pulled from both sides. In this general configuration, the forks rise twice the distance the cylinder moves.[4] If the cylinder extends by 1 meter, the forks rise by 2 meters. However, this is a general configuration, and not all models work exactly this way.
Even when raised high, the load remains sticking out in front of the vehicle body. Does this not cause it to fall forward?
2. Why a forklift doesn't tip forward with a load in front
Think of a seesaw at school. If a light child and a heavy child sit on it, the side with the heavy child goes down. But if the heavy child moves closer to the center pivot, the seesaw balances. This is explained by "moment of force." Moment is calculated as force multiplied by the distance from the pivot. If the clockwise and counterclockwise moments are equal, the seesaw stays still.[2]
In a forklift, the further the load moves away from the vehicle body, the greater the force trying to tip it forward. To prevent this, forklifts have a heavy weight called a counterweight at the rear to increase stability. The vehicle body is relatively heavy, and the top speed is slow, about 10 to 20 km/h (6 to 12 mph).[1]
When a load is added, the combined center of gravity of the vehicle and load shifts forward. US educational materials from the Occupational Safety and Health Administration (OSHA) explain that for the forklift to remain stable while stationary, this combined center of gravity must stay inside a triangle formed by the two front wheels and the center of the rear axle. If it moves outside this triangle, the forklift tips over.[5]
When moving, sudden braking or sharp turns can also cause tipping, so caution is needed. Note that this "triangle" explanation comes from US safety education and should be read separately from definitions in Japanese materials.
3. How the load's position changes a forklift's safe weight limit
Forklifts have a number called "maximum load capacity." This is the heaviest weight that can be placed at a standard load center. It is determined with the mast vertical and the top of the forks raised 300 mm (about 12 inches) from the ground.[1]
The key point is that the further the load's center of gravity is from the fork heel, the lower the allowable load capacity becomes on the capacity chart.[1] This is like a seesaw: if the heavy child sits at the very end, the other side must be much heavier to balance. Even with the same item, if it is long and its center of gravity is near the tip of the forks, the safe carrying weight decreases.
Even with a rear counterweight, there is an upper limit to how much can be carried because of these conditions. Next, we look at a different feature: steering.
Remember, if a load is long and its weight is concentrated at the front, the safe amount you can carry is smaller.
4. Why forklifts steer with their rear wheels
Imagine trying to insert forks under a load in a narrow warehouse aisle. If you are off-center, you might push the load instead of lifting it. For this reason, forklifts generally drive with the front wheels and steer with the rear wheels, which is the opposite of cars.[3]
The reason is to make driving easier in narrow spaces like warehouses.[1] It allows for tight turns, which is necessary to place the forks accurately under a load that is very close.[3] The front wheels provide the driving force, while the rear wheels change the direction.
Power sources include gasoline, diesel, liquefied gas, and batteries.[3] So, when did this machine come to Japan, and how did it spread?
5. How forklifts began in the US and Japan
In the US, forklifts are said to have been born in the early 1930s. At that time, handling small items relied on many workers.[2] The exact year of origin varies by source. Clark's company history lists a hydraulic lift truck in 1922 and an internal combustion forklift with forks in 1924. They claim it was the "world's first," but this is the company's own assertion.[6]
In Japan, it is told that Noboru Niwa, the first president of Toyo Transport Machinery (now TCM), decided to build forklifts himself after seeing US military forklifts brought to Japan.[2]
In 1949, four vehicles weighing 6,000 pounds (about 2.7 tons) were delivered to the Kobe Maritime Bureau. The first of these was recognized as a Mechanical Heritage by the Japan Society of Mechanical Engineers in 2010. It was valued for kick-starting Japan's logistics equipment development and reducing the burden of cargo handling at ports.[2]
In 1956, it is said that TCM forklifts were used in Antarctica, which became a topic of discussion.[2] Can you see a forklift in a warehouse or store today?
6. A ruler experiment to test balance with your own hands
Place a ruler halfway off the edge of a desk. Put an eraser on the overhanging end and a pencil case on the part resting on the desk. Find the position where it just barely doesn't fall. See if you need a heavier object at the back as you move the eraser further forward. This is the same idea as the forklift's rear counterweight.
If you can see a forklift from outside a store or warehouse, look for the rear counterweight and the position of the rear wheels. Do not approach it, as it is dangerous; just watch from a distance. If you cannot see the back, looking at the visible wheels is enough. Also, observe how high the forks are when lifting a load.
For more information, the Ministry of Health, Labour and Welfare training materials and the Japan Construction Machinery Association journal contain names of lifting devices and photos of the first Japanese model.[1][2]