Initially it looks like this:
Figure 463.1. a) the existing arc, b) determination of the segment chord length and height.
Thus, when there is an arc, we can connect its ends and get a chord of length L. In the middle of the chord we can draw a line perpendicular to the chord and thus get the height of the segment H. Now, knowing the length of the chord and the height of the segment, we can first determine the central angle α, i.e. the angle between the radii drawn from the beginning and end of the segment (not shown in Figure 463.1), and then the radius of the circle.
The solution of such a problem was considered in sufficient detail in the article "Calculation of an arched lintel", therefore, here I will only give the basic formulas:
tg( a/4) = 2H/L (278.1.2)
A/4 = arctan( 2H/L)
R = H/(1 - cos( a/2)) (278.1.3)
As you can see, from the point of view of mathematics, there are no problems with determining the radius of a circle. This method allows you to determine the value of the radius of the arc with any possible accuracy. This is the main advantage of this method.
Now let's talk about the disadvantages.
The problem of this method is not even that it is required to remember the formulas from the school geometry course, successfully forgotten many years ago - in order to recall the formulas - there is the Internet. And here is a calculator with the function arctg, arcsin, and so on. Not every user has one. And although the Internet also successfully solves this problem, we should not forget that we are solving a rather applied problem. Those. it is far from always necessary to determine the radius of a circle with an accuracy of 0.0001 mm, an accuracy of 1 mm can be quite acceptable.
In addition, in order to find the center of the circle, you need to extend the height of the segment and set aside a distance equal to the radius on this straight line. Since in practice we are dealing with non-ideal measuring instruments, a possible error in marking should be added to this, it turns out that the lower the height of the segment in relation to the length of the chord, the greater the error in determining the center of the arc.
Again, we should not forget that we are not considering an ideal case, i.e. This is how we immediately called the curve an arc. In fact, it can be a curve described by a rather complex mathematical relationship. Therefore, the radius and center of the circle found in this way may not coincide with the actual center.
In this regard, I want to offer another method for determining the radius of a circle, which I myself often use, because this method is much faster and easier to determine the radius of a circle, although the accuracy is much less.
The second method for determining the radius of the arc (method of successive approximations)
So let's continue with the current situation.
Since we still need to find the center of the circle, to begin with, from the points corresponding to the beginning and end of the arc, we draw at least two arcs of arbitrary radius. A straight line will pass through the intersection of these arcs, on which the center of the desired circle is located.
Now you need to connect the intersection of the arcs with the middle of the chord. However, if we draw from the indicated points not along one arc, but two, then this straight line will pass through the intersection of these arcs, and then it is not at all necessary to look for the middle of the chord.
If the distance from the intersection of the arcs to the beginning or end of the considered arc is greater than the distance from the intersection of the arcs to the point corresponding to the height of the segment, then the center of the considered arc is lower on the straight line drawn through the intersection of the arcs and the middle of the chord. If less, then the desired center of the arc is higher on the straight line.
Based on this, the next point is taken on the straight line, presumably corresponding to the center of the arc, and the same measurements are made from it. Then the next point is taken and the measurements are repeated. With each new point, the difference in measurements will be less and less.
That's actually all. Despite such a lengthy and intricate description, it takes 1-2 minutes to determine the radius of the arc in this way with an accuracy of 1 mm.
Theoretically, it looks something like this:
Figure 463.2. Determining the center of the arc by the method of successive approximations.
But in practice, something like this:
Photo 463.1. Marking a workpiece of complex shape with different radii.
I’ll just add here that sometimes you have to find and draw several radii, because there are so many things mixed up in the photo.
The correct choice of rims depends on the technical characteristics that indicate all parameters, namely the width, diameter, offset, as well as DIA (hub bore diameter) and PCD (drilling parameters).
You also need to know the marking designation. It indicates the standard parameters of any type of wheel products:
Markings are indicated on the inside. Usually, manufacturers duplicate them in the accompanying documents and on the packaging if the product is new.
Disk Options
To determine what the marking means, you need to know the width and diameter of the wheel product.
Drilling, or bolt pattern
This is one of the more difficult parameters to study, indicating the diameter of the mounting bolts. Drilling is measured from the center zone of the stud to the opposite zone of the element on the wheel.
Quite often, manufacturers indicate the parameters of the disc bolt pattern through a fraction, depending on the number of holes for fixing.
Suppose the indicators are 6/222.25. The first number indicates the number of holes for fastening bolts, and the second number indicates the number of holes drilled in millimeters.
Disk departure
This indicator is marked with the English letters ET. What is ET in discs and why is it? The indicator indicates the distance from the plane of the wheel product to the middle zone of the rim. The mating surface of the wheel product indicates the pressing plane of the disk to the hub.
Departure options can be:
- with a zero indicator;
- with negative;
- with positive.
Zero offset indicates that the plane of the disk corresponds to its middle zone. Thus, the lower the indicator, the more the wheel product protrudes from the outside of the vehicle. If the overhang is increased, this means that the disc is recessed into the interior of the vehicle.
It is also necessary to take into account the fact that, depending on the width of the product, the departure indicators differ. Manufacturers indicate in the accompanying documentation for the vehicle a lower offset value for wheels with a large width.
Diameter and other disk parameters schematically
What is HUMP (H)?
The hump is a protrusion of the ring on the disc rim. This element is used as protection against dismounting of a car tire. Usually 2 humps (H2) are used for the wheel.
In some cases, the hump may not be used, or only one is used, depending on the configuration of the car. Varieties of Humps:
- combined (CH);
- flat (FH);
- asymmetric (AH).
PCD disk options
The PCD value indicates the diameter of the circle of the center holes on the rim. That is, this is the diameter of the holes for fastening the bolts.
DIA disk option
The DIA parameter indicates the diameter of the hole located in the center of the disc. Casting manufacturers prefer to create a large diameter center hole DIA. This is done so that the discs are applicable and universal for any type of car.
Despite the fact that the size of the hub may differ depending on the model of the vehicle, the auto disk is installed using an adapter ring, bushing.
Marking
As an example, consider the wheel rim marking 9J x20H PCD 5×130 ET60 DIA 71.60:
- The number 9 indicates the width measured in inches. To convert inches to centimes, the total is multiplied by 25.4.
- The letter J indicates structural elements: the shape of the disk flanges. This parameter does not play an important role in the selection.
- The letter X stands for inseparable disk.
- The number 20 indicates the diameter of the fit of the wheel product. This indicator corresponds to the fit of a car tire.
- The letter H denotes the presence of one hump or protrusion on the rim.
- Abbreviation PCD 5×130, where the number 5 indicates the number of holes for fastening nuts or bolts and the number 130 indicates their PCD diameter in millimeters.
- The ET60 marking indicates disc offset. In this situation, the indicator is 60 mm.
- The DIA value of 71.60 indicates the diameter of the center drill. Usually, DIA corresponds to the fit of the hub and is indicated in millimeters. If the DIA is larger than the hub diameter, then a center fit ring is used to install the disc.
Information is also attached to the label:
ISO, SAE, TUV - these abbreviations indicate the organizations that performed the inspection of the wheel product, similar to the Russian GOST. Standards that correspond to the wheel marking are also indicated.
Maxload indicates the allowable load on a car wheel. This indicator is indicated in kilograms and pounds.
What does parameter 700c mean?
This designation is used for large types of wheels for SUVs and Niva. According to the accepted ISO classification, this figure is 29 inches. Typically 700c wheels are used for off-road racing.
By using 29 inch wheels:
- improved management performance;
- the braking distance on unpaved surfaces is reduced and aerodynamics are increased;
- the car's patency on soft soils and sands increases;
- it becomes possible to install powerful brakes.
In order to select the wheels corresponding to a particular type of car, it is recommended to determine the diameter of the wheel and analyze the markings indicated on the rim. Also, do not forget that this element ultimately depends on safe driving.
Source kolesadom.ru
Reading time: 4 minutes
Car rims not only improve the appearance of the vehicle, but also increase the smoothness of the ride. Due to its unique properties, modern developments provide the most comfortable and safe ride under any climatic conditions. When purchasing new designs, motorists are repeatedly faced with the problem of how to choose them correctly. This question is relevant for both beginners and experienced drivers. There are many design parameters that need to be determined in advance in order to improve the driving performance of a car. For example, the main parameter is the width of the disk, which is responsible for the safety of the driver / passenger.
Disc width
As a rule, the diameter and placement of holes are far from the most important parameters when choosing components. At the same time, the marking indicated on the back of the product is not clear to all motorists. When choosing designs for your own car, it is imperative to determine the possible width for a given tire size.
Construction width
When choosing car wheels, you need to consider the dimension of the tire. With a diameter, everything is usually clear, for example, a tire with a dimension of R15 should be installed on a wheel with a diameter of 15. Basically, the problem arises from determining the width of the tire and disk.
Table: wheel width, profile height in mm
You can do the calculation yourself. To do this, consider an example for a tire with a width of 215 mm and a diameter of 16.
- The width of the rubber is indicated in centimeters: 215 mm = 21.5 cm.
- Next, you need to translate the resulting value into inches: 1 centimeter \u003d 2.54 inches, divided by 21.5 by 2.54, it turns out 8.46. The amount can be rounded up to 8.5.
- From the value obtained, 25-30% is taken, in this embodiment, 2.38 is obtained.
- The resulting number can be subtracted from the tire width and rounded up to tenths 8.5 - 2.38 = 6.1.
- The rim size of the product must be 6.1 inches or 155 mm.
- Designs that have a diameter of up to 14 inches, their possible error is determined from 0.5 to 1.
- Products that have a diameter of 15 inches are found with an error of up to 1.5.
Why is it important to correctly determine the width of the car disk
To find out what the width of the rim especially affects, each car owner must understand that any deviation from the requirements of the manufacturer regarding the technical parameters of the structures may cause suspension failure. This unfavorable factor contributes to the rapid wear of components, as well as chassis parts. Not taking into account every parameter, you may encounter structural failure while driving.
What is the width of wheel castings measured in
Before choosing the appropriate product for a car of any brand, it is necessary to consider an example of design marking: 6.5 14 4 × 100 ET45 D54.1:
- 6.5 - width is determined;
- 14 - diameter of the structure;
- 4×100 - information about the fastening of the structure;
- ET45 - departure;
- D54.1 - bore diameter.
Low profile models are durable. Therefore, before measuring the width of the structure on a car of any brand, it is better to check in advance all the information that is indicated on the label. To increase the speed characteristics, it is necessary to take into account the recommendations of the manufacturer.
Disc parameters 7J in centimeters
J is one of the important parameters that indicates the design features of the side flanges of the rim of the wheel product. Usually, the following combinations are most often indicated on the marking: J, JJ, JK, K, B, D, P.
What affects the width of the autodisk
Each cast or forged wheel needs a personalized rubber option that will fit the main parameters of the manufacturing plant. With the wrong choice, you can face a number of problems. It is difficult to miscalculate with the diameter, because setting the wrong size is problematic. But it is quite easy to make a mistake in terms of width. Too narrow or wide designs will adversely affect the design profile of the tire. This will result in performance degradation, such as reduced sidewall stiffness.
What effect does the width of the autodesign have?
Many people often wonder what the width of the rim affects. Experts say that the size of the rim of the product should be 25% less than the width of the rubber profile. For the size 195/65 R15 91 T shown, the construction width can be calculated as follows:
- First, the width of the profile is calculated.
- Next, 195 should be divided by 25.4, resulting in 7.68 inches.
- Subtract 25% from this value, and then round the result.
- The formula looks like this: 195/25.4-25%=5.76.
- Further, the number needs to be rounded up and you get a disk 6 inches wide.
It makes no sense to install components with increased width without replacing rubber, the behavior of the machine changes only within the measurement error. If the disc is heavy, then it contributes to the deterioration of the ride and handling of the vehicle.
Source kolesa.guru
The rim is one of the most critical parts that connect the car to the road through the tire. When replacing tires or buying new wheels, it often becomes necessary to find out the parameters of the wheel. Deciphering the markings of disks and other designations on them will help you understand all the parameters and characteristics of your wheels.
Most of the characteristics of rims affect ride safety and suspension uptime. When choosing discs, you need to find out which models with what characteristics are allowed to be used on your car. Only if all requirements are met can they be installed on the machine.
Our website already has instructions for decoding tire markings, and now we will explain how to decipher the markings on rims.
You may also find our visual tire calculator useful.
Disc markings
Stamped and alloy wheels for passenger cars have the same standard designation (marking). Certification of discs in the territory of the EU countries is carried out according to UN/ECE 124.
As an example, one of the options for marking a rim can be deciphered: 7.5 J x 15 H2 5x100 ET40 d54.1
The decoding of this marking will be as follows:
Rim width
The number 7.5 in the marking example indicates the distance between the inner edges of the rim in inches. This indicator is taken into account when choosing tires, since each tire has a certain range of rim widths. It is best when the rim width is in the middle range of the tire.
Rim edge type (flange)
The Latin letter J in the disc marking indicates the shape of the rim flange. This is where the disk connects to the bus. Among the most common designations for cars are: P, D, B, K, JK, JJ, J. Each letter hides several parameters:
- radius of curvature
- profile contour shape,
- shelf angle,
- shelf height, etc.
Most often in modern passenger cars there is a rim in the form of J. All-wheel drive models are usually equipped with disks with the JJ type designation.
The flanges of the rim of the rim affect the mounting of the tire, the mass of the balancing weights, the resistance of tires to displacement in extreme situations. Therefore, despite the external similarity of the JJ and J rims, the rim edge recommended by the automaker should be preferred.
Rim split
The "x" sign indicates that the rim is made in one piece and is a single unit, and the "-" sign indicates that it consists of several components and can be disassembled and assembled. One-piece discs differ from collapsible structures in lightness and greater rigidity.
Wheels with an "x" rim are designed to be used with elastic tires, which is typical for cars and light trucks. In the case of truck tires, which differ in rigidity, split disc designs are required. It is simply impossible to mount a tire on a rim in a different way.
Mounting diameter (rim diameter)
Mounting diameter - this is the size of the landing rim of the rim under the tire.
The mounting diameter is usually indicated in inches (in our example, this is the number 15). In everyday life, motorists also call it the radius of the disk. When selecting a tire, this indicator must necessarily match its mounting size.
The standard values of mounting disc diameters for cars and crossovers will be from 13 to 21.
Ring ledges or rolls (hump)
The designation H2 is deciphered as follows. Ring protrusions (humps) are located on 2 sides of the disc. These rolls are designed to fix the tubeless tire on the rim. They prevent the outflow of air in case of external impact on the tire. Other notations apply:
N - there is a hump on one side only,
FH - the tackle has a flat shape (Flat Hump),
AH - the ledge has an asymmetric shape (Asymmetric Hump), etc.
Mounting Hole Location (Pitch Circle Diameter)
In the 5x100 marking, the first number indicates the number of holes in the rim. The number 100 indicates the diameter of the circle on which the mounting holes are placed.
- The number of mounting holes for cars usually ranges from 4 to 6 pieces.
- The standard values for the diameter of the circle will be 98 ÷ 139.7.
It is not always possible to determine by eye the correspondence between the size of the hub and the disk. And installing a disc 98 instead of 100 can lead to wheel misalignment, which will cause beating, as well as spontaneous loosening of the bolts.
Disk offset (ET, Einpress Tief)
The offset of the disk is the distance between the contact plane of the disk with the hub and the plane that passes through the center of the cross section of the wheel disk. The value is expressed in millimeters, and the overhang can be either positive (ET40) or negative (ET-30).
Bore diameter (hub diameter, DIA)
The central (hub) mounting hole of the rim is indicated in millimeters, for example d54.1. The diameter of the landing hole in cars ranges from 50 to 70 mm. It is very important to accurately select the disc in accordance with the landing belt of the vehicle hub.
Even with slight deviations of one of the parameters of the rim from the requirements of the automaker, there is a threat of accelerated tire wear, which can lead to its destruction in an extreme situation (high speed, sudden braking, sharp turn).
When the car stops due to the fault of the engine, you can call a tow truck, a foreman, or leave for help on a ride. But when a tire ruptures at high speed or a wheel comes off the hub, this creates a danger to the life of the driver, passengers and other road users. Therefore, the wheels must always be in good condition and be under the constant control of the driver.
When we choose a car for ourselves, we evaluate the main key characteristics, such as the dimensions of the car, the output and engine size, the type of gearbox, and so on. But for everyday operation, other indicators are also important, for example, the turning radius. How does this parameter affect driving, how is it measured, and what is it all about?
From the name of the parameter it is already clear that it means the radius of the (minimum) semicircle described by the machine during a turn maneuver performed from a standstill. The steering wheel must be turned all the way. Everything seems to be clear, but this parameter has its own nuances.
How important is the parameter
The turning radius is one of the components of the maneuverability of the car, the larger its value, the more space is required to turn the car. This affects the ability of the car to turn around on a limited road width in one go. With a small radius, the car is easier to drive in urban areas, and it is also easier to park. Automakers, in the desire to show their cars more maneuverable, enter the minimum value into the documentation, that is, along the wheels, from curb to curb, because it turns out to be significantly less than the real one from wall to wall. So, when choosing a car for this parameter, we also take into account the size of the front overhang.
How important is the turning radius?
How we measure
It is easy to measure the radius: we mark the starting position of one wheel (outer), turn the steering wheel to the end, turn to full 180 degrees, mark the final position of the same wheel. We measure the distance between the marks, half of it will be the turning radius. This size is the minimum width of the road (namely, the smooth part), which will allow you to turn around in one go.
This is in theory, but in practice you will have to take into account the size of the front overhang of the car, this is the distance from the front axle to the tip of the bumper. The fact is that the width of the road is not always limited by a low curb, there are often chippers, and the curbs themselves can be up to a meter high. And if the turning radius fits well into the ideal road, then with high limiters you may not fit in. So the real radius is measured a little more complicated - you need to install an overhang with chalk on the outside of the bumper (you can on the rod), after turning the chalk will leave marks on the real radius.
Turning radius in parking lot
Nuances
The main nuance or problem is in terminology, the turning radius, it is rather a colloquial term, in fact, the diameter will be correct. And different manufacturers may indicate different indicators, who is the radius and who is the diameter, this should be taken into account and specified. For example, Toyota's Prado is advertised as having a turning circle of less than six meters, while the car itself is almost five meters long. Such a diameter is simply impossible. In the guide for the car, it is said about the radius measured along the wheels, that is, a value that can be considered correct. On some sites in other countries, the diameter itself is indicated, which is more than 11 meters, which is very similar to the truth.
Do we change the parameter
What is the turning radius? Firstly, from the dimensions of the car, of course, it will not work to change them. Secondly, on the angle of rotation of the front wheels. In general, changing the radius without serious intervention in the main structure will not work. And this is a loss of warranty, as well as possible problems with stable operation. Usually such alterations can be found on drift cars, where eversion is maximized. True, this is not done to reduce the turning radius, but to increase the drift angle that the car can hold. It is better not to alter ordinary civilian vehicles.
Drift turning radius
How to measure the radius of a circle! ? I forgot how to measure it is necessary to remind someone! and got the best answer
Answer from Loch Silver[guru]
ruler, measure the largest distance of the circle, this will be the diameter, divide in half_this will be the radius
Loch Silvery
Thinker
(9085)
I wrote-measure with a ruler the largest distance between the two edges of the circle
Answer from freddy bags[newbie]
Thank you
Answer from Yaisiya Konovalova[guru]
To determine the radius of a circle, you must first find its center.
To find the center, we draw a chord (a straight line connecting two points located directly on the circle itself). Determine the middle of the chord (divide the segment in half with a ruler). We draw a straight line through the middle, perpendicular to the chord, that is, so that the angle is 90 degrees. Then we draw another chord and repeat with it all the same as with the first.
Determine the point of intersection of the perpendiculars. This point is the center.
. Let's extend any of the perpendiculars to the intersection with the line of the circle. Measure with a ruler the distance from the resulting intersection point to the center of the circle.
This distance will be the radius of this circle.
Answer from 2 answers[guru]
Hello! Here is a selection of topics with answers to your question: HOW to measure the radius of a circle! ? I forgot how to measure it is necessary to remind someone!
