The organization of a full-fledged workplace in the garage often rests on the lack of access to the bottom of the car. The classic observation pit requires serious excavation work as well as high groundwater levels, making its construction impossible in many regions. It is in these situations that the first step is taken. mini-flyThe size of the structure allows you to place the structure even in a limited space.
This is a stationary or mobile elevation, allowing you to drive the wheels on the supports and access the bottom, the engine from below, the exhaust system and suspension elements. Unlike jacks, the overpass provides a stable platform, eliminating the risk of a car falling and injuring the master. Proper calculation of dimensions here is a critical safety factor.
When planning construction or buying a finished product, it is necessary to take into account not only the dimensions of the vehicle itself, but also the convenience of work. Too narrow or low design will make repairs impossible, and too high can become dangerous on arrival. Let’s take a look at all the technical parameters that affect the choice of optimal configuration.
Standard dimensions and geometric parameters
The main parameter from which design begins is height. For comfortable work under the car, an adult requires a certain space. The minimum permissible value is considered to be a height of 500-600 mm, but the optimal solution for most garages is the range from 700 to 900 mm. This allows you to work standing or sitting on a low stool without experiencing discomfort in the back.
The width of the design directly depends on the track of the serviced cars. If you plan to serve only passenger sedans, then the width of the carriageway may be narrower than for SUVs or minibuses. Mid-gauge In passenger cars, the range ranges from 1400 to 1600 mm, so the useful width of the flooring should be at least 2 meters, so that the wheels are guaranteed to fall on the platform even with an imperfect race.
The length of the overpass also plays an important role, especially if you plan to drive the car completely. For a partial check-in (only the front or rear part) a length of 2.5-3 meters is sufficient. However, for a full inspection of the entire chassis and exhaust track, the length of the platform should be at least 4.5-5 meters.
The angle of inclination of the raceways is the parameter that is often neglected, which leads to damage to the bumpers or "tweeting" the bottom. For low-end vehicles with clearance less than 140 mm, the angle of entry should be flat. The optimal length of the upper ramp is 1.5-2 meters with a height difference of 70 cm. The steep rise can be an insurmountable obstacle for sports cars.
⚠️ Attention: When calculating the width, be sure to take into account the margin of 20-30 cm on each side. If the wheels slide off the edge of the platform while working, the consequences can be fatal for the wizard under the machine.
Materials of manufacture and their influence on size
The choice of material dictates not only the durability of the design, but also its final dimensions. Metal overpasses made of a channel or profile pipe have high strength with a relatively thin profile. Steel allows you to make wide spans without additional supports in the middle, which makes it easier to remove garbage and oil from under the car. The thickness of the metal for the supporting elements should not be less than 4-5 mm.
Wooden mini overpasses are less common, but have the right to exist as a temporary or budgetary solution. Here. bar-size It must be significantly larger than the metal pipe profile to support the weight of the vehicle. Usually used bar cross-section of at least 150x150 mm or 200x200 mm. This increases the overall height of the structure, but simplifies installation with your own hands.
Combined options, where the frame is metal, and the flooring is made of a thick board or plywood, are a compromise solution. The tree here acts as an anti-slip coating and a thermal insulator, which is relevant in winter. However, it is worth considering that the tree will eventually decay or rot, requiring replacement, which may slightly change the geometry of the decking.
Concrete overpasses are built less often due to labor-intensiveness, but they have a monolithicity. The dimensions of concrete walls usually make at least 250-300 mm thick to ensure strength. This eats up useful space in the garage, so such designs require careful planning even at the stage of pouring the foundation.
Use a grooved metal sheet or welded rebar on the surface of the raceways – this will prevent wheels from slipping, especially in rainy weather or winter.
Load calculation and strength characteristics
When determining the size, one should not forget about the loading capacity. A passenger car weighs an average of 1.2 to 2 tons, but SUVs and commercial vehicles can reach 3-4 tons. The design should have a safety margin of at least 2-3 times the planned weight. This applies not only to the thickness of the metal, but also the number of support racks.
Load distribution is a key point. If you make a flyover with a central support or multiple crosses, make sure that they will not interfere with the sagging of the suspension elements when lifting the wheels. Passage between supports shall be so designed that no critical deflection of the load-bearing beams under maximum load occurs.
For heavy jeeps, it is recommended to increase the number of longitudinal beams. If two main guides are enough for a sedan, then for heavy equipment it is better to provide a solid flooring or four support lines. This will prevent deformation of the car frame and the overpass itself.
⚠️ Attention: Never save on welds and fasteners. When lifting the car, the center of gravity shifts, and the dynamic load during braking on the overpass can exceed the static weight of the car by 1.5 times.
The safety margin of the structure should be at least 200% of the weight of the heaviest car to be serviced.
Types of constructions: stationary vs mobile
The size of the mini overpass depends on its type. Stationary structures are built into the garage floor or installed permanently in one place. Their dimensions can be any, limited only by the size of the room. Often they are performed in the form of a U-shaped structure, where the car stands over a recess or between two parallel walls.
Mobile (prefabricated) overpasses are a modern trend for those who do not have the opportunity to build a capital structure. They consist of four separate ladders (two front, two rear) or two single platforms. The dimensions of such modules are standardized for ease of transportation in the trunk. The width of one ladder is usually 300-400 mm, and the length is about 2 meters.
The advantage of mobile models is their versatility: you can only spread them under the front of the oil change car or under the entire exhaust repair machine. However, they require a perfectly flat floor in the garage. On an uneven surface, the mobile overpass can stagger, which is unacceptable when working under the car.
Folding overpasses occupy a minimum of space in folded form. Their dimensions in the transport position allow you to store them vertically against the wall. The unfolding mechanism is usually simple and requires no tool, but requires regular lubrication of the hinges to prevent backlashes.
Ergonomics and safety at work
The dimensions of the overpass should provide not only access to the units, but also the safety of the master. The width of the corridor between the wheel ladders must be sufficient for the free movement of a person. The optimal width of the free space between the tracks is 600-800 mm. This will allow you to sit comfortably on a chair with wheels and move tools.
The height of the side or the presence of travel limiters is an important element of safety. Even small sides 50-70 mm high at the edges of the collision will prevent accidental wheel descent. If the overpass is high, such limiters are mandatory. Some designs use removable stops that are installed after the car arrives.
The lighting of the working area also depends on the dimensions. Under a high overpass is often dark, so the size of the structure should allow the suspension of portable lamps or the installation of stationary lighting under the deck. Cable channels for electricians are better to lay immediately when designing dimensions, hiding them inside the support poles.
Ventilation under the overpass is another nuance. If the structure is deaf and high, exhaust gas or fuel vapor can accumulate under it. Therefore, it is recommended to make the flooring not solid, but with gaps or perforation, which also reduces the weight of the structure and facilitates cleaning.
How to make the overpass adjustable in height?
Some masters make a flyover with the possibility of changing the height of the supports. For this purpose, telescopic tubes or a system of holes are used to rearrange the crossbars. This allows you to adjust the height for different tasks: low for quick oil change, high for serious repairs. However, such a design is more difficult to manufacture and requires very reliable fixtures.
Comparative table of overpass parameters
To systematize the information and help you decide on the choice, we will compare the main types of structures in numerical values. These data are averaged and can vary depending on the project.
| Parameter | Stationary (metal/concrete) | Mobile (command) | Mini flyover (for butter) |
|---|---|---|---|
| Height of lift | 700-900 mm | 300 - 500 mm | 150 - 250 mm |
| Length of work area | 4000 - 5000 mm | 2000 - 4,000 mm | 1000 - 1500 mm |
| Width (total) | 2200 - 2,500 mm | 1800 - 2200 mm | 1600 - 1800 mm |
| Structural weight | Heavy (real estate) | Medium (portable) | Light (single seat) |
| Difficulty of installation | Tall. | Low. | Minimum |
As you can see from the table, The optimum height for universal use is 700-800 mm.This allows a person of average height to work under a machine without having to lie down on the ground. Mobile versions win in versatility, but lose in height.
Instructions for Selection of Sizes for Your Garage
Before starting construction or purchase, take measurements of your garage. Consider not only the length and width of the room, but also the location of the gates, shelving and other objects. The overpass should not block the passage and should allow the car doors to be opened when it is standing on it.
Identify a task list. If you only change the oil and filters, you don’t need a full four-meter overpass. Enough mini-version under the front. If you plan to overhaul the suspension or replace the muffler, then you can not save on the length.
☑️ Checklist before construction
Don't forget to drive. Before the overpass should be free space equal to the length of the car plus 1-1.5 meters for acceleration and alignment. If the garage is short, you may have to make a flyover with a through passage or with the possibility of reversing, which requires additional security measures.
⚠️ Attention: When building in a finished garage, make sure that the floor will withstand the point load from the overpass supports. A weak screed can crack under the weight of the structure and the car, which will require expensive foundation repairs.
Frequently Asked Questions (FAQ)
What is the minimum height of the overpass allowed for oil replacement?
To replace the oil, a height of 150-200 mm is enough to substitute the container and unscrew the plug. However, for a full inspection and key work, a height of 400 mm is more convenient. Making a flyover below 150 mm does not make sense, since it is easier to use a jack.
Can you make a tree trestle?
Yes, you can. For this purpose, use a timber 150x150 mm or 200x200 mm. Wood is cheaper than metal, does not require welding, but is less durable. It must be treated with antiseptics and flame retardants, and regularly checked for cracks and rot.
Do I need a viewing hatch inside the overpass?
In classic overpasses (two-tub) hatch is not needed, as you work between the tubes. If the overpass is made in the form of a single platform, the hatch (laze) is necessary to access the center of the bottom. The size of the hatch must be at least 600×600 mm.
How to calculate the length of the raceway?
The length of the ladder depends on the height of the lift and clearance of the car. The formula is simple: the lower the clearance, the longer and more should be the ladder. For a standard sedan and a height of 50 cm, the optimal length of the ladder is 1.5-2 meters. For low-priced cars - up to 3 meters.
Is it safe to work under a mobile overpass?
Work under any overpass is safe only if the rules are followed: flat floor, serviceability of the structure, the presence of wheel limiters and stops (shoe) placed under the wheels. Mobile overpasses must have an anti-slip coating and rigid wheel fixation.