What is the ground clearance of a car and 6 ways to increase it
Content
There are quite tense disputes about the terminology in the definition of the concept of ground clearance. It comes to the point that they begin to look for differences between ground clearance and clearance. In fact, this is the same thing, the literal translation of the English "clearance".
But there are nuances, especially since in many cases this characteristic of the vehicle becomes one of the most important, determining the very possibility of further movement.
What is called clearance in the car
There are several definitions, depending on the country and the accepted standards by the industry and consumers.
It's all about finding the measurement point from the closest part of the car to the road to the surface, which defines the concept of clearance.
- According to the current Russian GOST, ground clearance is measured as the distance from the lowest point to the road, but only in the central part of the bottom and chassis.
And this is a rectangle, front and back limited by the dimensions of the car, but on the side only by vertical planes that form an area of \u80b\uXNUMXbXNUMX percent distance between the inner surfaces of the tires.
This is done so as not to take into account low-lying suspension elements, mudguards and other parts that are actually protected by the proximity of the wheels.
The measurement is made under a load that forms the maximum permitted weight of the vehicle.
- The German standards pursue roughly the same goal, but in a different way. An arc of a circle is drawn, inscribing the inner sides of the wheels and the lowest point of the body. The combination of such arcs forms a cylinder, along which the car theoretically could pass without catching it with the body and chassis.
The minimum height of this cylinder above the road will be the clearance. Thus, for example, the protrusion of the axle gearboxes of an SUV will not be taken into account if they are shifted to the side from the longitudinal axis of the vehicle, which is quite logical for driving in a track.
- In military technology, compromises are excluded. Nothing should touch the ground when measuring ground clearance. Therefore, the entire area under the bottom is used.
- Sometimes two clearances are negotiated, one under the drive axles of a continuous structure, and the second under all other parts that have suspension. This makes sense for SUVs, since it is important to track the change in ground clearance when the suspension is working. The distance from the lowest point of the bridge does not change, but this is not important, the rigid casing is adapted for cutting through the soil on the crest of the track.
Clearance is usually highly dependent on the load of the machine. Hence the discrepancies in its assessment. Not all manufacturers clearly stipulate the measurement method.
As a result, many crossovers actually have 15-17 centimeters from the declared 12-14 centimeters even after the car is partially loaded. Especially if the dealer installs additional protection for the power unit, without which it is very undesirable to drive.
What are overhang angles
In many cases, car overhangs become an equally important indicator of geometric cross-country ability.
These are the distances in front and behind from the contact patches of the wheels with the road to the external dimensions of the car. But by themselves, they do not affect operation as much as the corners that form at the same time, because the details in the overhangs can be located quite high.
If a line is drawn between the point of contact and the lowest part of the overhang, then the angle between that line and the road plane becomes the overhang angle, more accurately referred to in the standard as the entry or exit angle.
Since, by definition, there are no body or frame elements in these corners, their increase allows you to drive up to obstacles without damage and jamming, for example, to park over a high curb or overcome a steep climb with a sharp break in the profile.
Most often, corners are limited by bumpers, exhaust system elements or attachments.
The swiftness of the appearance of the car suffers greatly from beveled and high-mounted bumpers. You can, for example, see how this was decided in the front of the Lexus RX crossover of the first and second generations, and how cross-country ability was deliberately sacrificed in the third, and especially in the fourth generations.
The angle of the rear overhang is usually easier, where it increases thanks to the design idea of an aerodynamic pseudo-diffuser.
How to measure the ground clearance of a car
To measure the ground clearance, it is enough to install the car on a flat surface, load it to the required level, fully or partially, and find the lowest point under the bottom in the area approximately 10 centimeters away from the inner surface of the wheels.
Usually this is a sheet of protection under the crankcases of the engine and transmission, or in the case of off-road vehicles - the “apple” of the stocking of the drive axle gearbox.
There are also design errors, when the elements of the exhaust system, fuel tanks, and even the bottom of the body with electrical wiring, brake and fuel lines are the lowest. Rough roads are categorically contraindicated for such cars without taking protective measures.
You can measure the distance from the found point to the road with an ordinary tape measure. Knowing the ground clearance, you can more accurately predict the safe passage of the car over possible obstacles.
Flexible parts, such as mudguards, can be omitted, they will not be damaged in any way.
How to increase ground clearance
If desired, the ability of the machine to overcome obstacles can be improved independently. There are several ways that differ in the correctness of obtaining the desired result.
Disposals
This is one of the most effective methods. It is usually called a suspension lift. In this case, specially made spacers are used, placed between the elastic and damping elements of the suspension (springs and shock absorbers) and their attachment points on the body. The type of spacers depends on the type of suspension.
In the most common case, when the suspension is made according to the MacPherson principle, where the springs and shock absorbers are combined into racks, spacers are placed between the upper supports and body glasses. The height of the spacers is usually about 3 cm, with possible deviations.
With this amount of lift, the characteristics of the car will change slightly. Exceeding this can cause problems with handling, wheel alignment and a reduction in the life of the drives.
Long or hard springs
The use of elastic elements with other properties, for example, springs with an increased bar thickness or additional coils, strictly speaking, is not a suspension lift.
The mounting points of the shock absorbers are not transferred, the suspension travel changes, and the clearance is highly dependent on the load. The incorrectness of this method is obvious, but it is still used, since it is quite simple to use.
It is enough just to buy and install springs from another car, modifications, or specially manufactured by tuning companies.
Typically, the kit specifications indicate the amount of lift, but it is not clear under what load, since the combination of changes in length and stiffness requires calculations.
Pneumohydraulic suspension (air springs)
The use of compressed air cushions, in combination with hydraulics or without, is possible in various ways, both as spacers and additional elastic elements.
Accordingly, it all comes down to one of the cases described above. But there are two benefits:
- clearance can be changed quickly from the driver's seat;
- in parallel, it becomes possible to adjust the stiffness of the suspension.
Often, the method is combined with the installation of adjustable shock absorbers, which gives control of dynamic stiffness and turns a simple suspension into an adaptive one. Such alterations provide the maximum effect, but also cost a record high.
High profile tires
Changing the geometry of the tires quite correctly increases the ground clearance while maintaining the suspension properties selected by the factory, but only possible to a limited extent:
- large wheels begin to touch the arches and chassis parts when driving over bumps and cornering;
- the dynamics of the car is deteriorating, which requires alterations in the transmission;
- large slip angles reduce handling on asphalt.
However, larger tires are almost always fitted when tuning SUVs, often with wheel arches trimmed, suspension and body lifts made, gear ratios of gearboxes and transfer cases changed.
Larger discs
Increasing discs is used extremely rarely to increase ground clearance. More often this is required to improve the appearance or accommodate more powerful brakes.
Although it is quite possible in cases where it is required to increase the rolling radius of the wheel, and you do not want to change the rubber profile for reasons of maintaining controllability.
The use of interturn pillows (buffers)
The method is as simple as it is incorrect. Between the coils of the springs there are additional elastic elements made of rubber or polyurethane, which change the stiffness of the suspension.
Ground clearance really increases, the car acquires some rigidity in reactions, which is mistaken for sportiness.
But at the same time, the suspension is completely unbalanced, the risk of spring breakage increases due to uneven load on the coils, and the rebound travel of the shock absorbers decreases.
In fact, this is a cheap version of using stiffer springs, but with an additional decrease in reliability. Suitable only for using the machine as a truck, especially with a trailer. Subject to constant monitoring of the state of the suspension.
Increasing the clearance is an unsafe undertaking, therefore it should be carried out by a qualified specialist, and the driver is warned about the consequences. The right decision would be to change the car to a more suitable one, where the clearance is factory-set.
