What should be considered when changing wheel-tyre combination?

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What should be considered when changing wheel-tyre combination?

The rim designation for car rims can appear very confusing at first glance. It summarizes the most important information about the rim. In order to decipher this information, the basic components of a rim should be known.

The structure of a rim consists of the following components, among others:

Rim shoulder
The edge on the outer surface of the rim ensures that the tire has a firm seat on the rim and is referred to as the rim shoulder.

Rim flange
The two rim flanges are steps that represent the outermost parts of the rim. They come in different forms. The most common is the “J” shape.

Hump
The hump is an elevation on the inner surface of the rim, which ensures that the tire cannot slip off the rim when cornering. The hump is also available in different versions.

Rim well
The area of ??the rim that is located between the two rim flanges is called the rim well.

Hub bore The hub bore
is in the middle of the rim. It serves to center the rim on the car’s wheel hub.

Bolt circle
This describes the holes, which are arranged in a circle around the hub hole, for fixing the rim with wheel bolts or stud bolts.

The most important dimensions
The most important dimensions can be derived from these components of the rim:

rim diameter
jaw width
offset
bolt circle
The rim diameter is the measurement between the rim shoulders in inches. So the diameter of the visible rim. Common sizes range from 13 to 22 inches.

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The inner width or rim width results from the distance between the two rim flanges, i.e. it describes the size of the rim cross section. The measurement is also given in inches and usually increases as the rim diameter increases.

The offset is the dimension from the center of the rim to the inner contact surface of the wheel hub. This distance is given in millimeters, unlike diameter and width. Different offsets of a rim can be used to vary how far the rim stands in the wheel arch.

The last dimension refers to the hole circle. This describes the number and position of the holes for the wheel bolts or bolts and is also given in millimeters. For example, if the pitch circle is specified as 5 x 112, the rim has 5 holes that are evenly spaced on a circle of 112 millimeters in diameter around the hub hole.

Example: 8 J x 18 H2 ET 45 LK 5×112

Rim cross-section: 8 inches
Rim flange shape: J
Structure of the rim: x
Rim diameter: 18 inches
Hump ??design: H2
Offset: 45 millimeters
Bolt circle: 5 holes, bolt circle diameter of 112 millimeters
What must be considered when changing the rim size?
First and foremost, it is important whether a change to the rim or the wheel-tire combination is permissible at all.

In order to find out whether the desired wheel/tyre combination and the offset are approved by the manufacturer, the vehicle registration document or the instructions for use provide information. There are also many tire and rim dealers online who offer the option of finding approved and even possible rim sizes using the car’s chassis number.

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Correct lock circle and wheel bolts
When choosing, it is important to select a rim model with the correct bolt circle. In addition, it may be that different wheel bolts have to be used for a different rim. This can be found out in the expert opinion of the rims or from the rim manufacturer.

Position of the rim in the wheel house
If an unregistered combination of rims and tires is to be fitted anyway, or if a change is pending in connection with a conversion of the chassis, a number of things are important for subsequent registration: The outermost edge of the wheel must not protrude beyond the fender out of the wheel arch. Likewise, under no circumstances should the tire rub against the inside or outside of the wheelhouse liners. Particular attention should be paid to this in the case of lowered vehicles. In the case of chassis conversions with a wheel/tyre combination that is not standard, it may be necessary to limit steering on the front axle. This reduces the maximum steering angle and thus prevents the tire from coming into contact with the wheel arch or other parts.

Change in tire size
A different rim size also means a change in tire size. So that the rolling circumference of the wheel remains the same with a different rim diameter, the cross-section of the tire must be adapted to the rim. Likewise, only certain tire widths are permitted on the respective rim cross-sections. The permitted tire dimensions for the respective cross-section can be viewed in various tables on the Internet.

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