Existing
Desired
ResetExample values

Tire calculation and/or rim calculation

Tire size
Warning
1: Existing tire / rim
Tire width?
105 - 405 mm
Tire height
25 - 100 %
Tire height?
20 - 55 inch
Tire width
5 - 15 inch
Diameter
5 - 25 inch
Rim width?
3 - 15 inch
Offset
-165 - 165 mm
Spacer washer
0 - 150 mm
2: Desired tire / rim
Tire width?
105 - 405 mm
Tire height
25 - 100 %
Tire height?
20 - 55 inch
Tire width
5 - 15 inch
Diameter
5 - 25 inch
Rim width?
3 - 15 inch
Offset
-165 - 165 mm
Spacer washer
0 - 150 mm
1: Enter values
Information
INFORMATION: The ratio of tire width to rim width does not correspond to the standard!
Warning
ATTENTION: Entries (highlighted in red) are out of range! Please correct your entries!

Results

 Existing
 Desired
Tire circumference
?
Rolling circumference
?
Tire height (sidewall)
?
Tire diameter
?
Rim size
?
Rim width
?
Poke (Outer Edge)
?
Inset (Inner Edge)
?
Show results in

Comparison & differences

Circumferential difference
Difference in rolling circumference
?
Speedometer display at real 100 km/h
Speedometer display at 100 km/h
?
The following differences also arise:
Difference in ground clearance
?
Change to the outer edge of the rim per side
?
Change to the inner edge of the rim per side
?
Placeholder

Graphic display appears after entering values

The strut illustration is for illustrative purposes only
2: Read the result

Note the difference in rolling circumference:

Rolling circumferences are generally approved in the range +1.5% und -2.5% g. Please check with the responsible inspector beforehand.

Speed deviation outside the norm:

In EU countries, the speedometer may display a maximum of +10 % + 4 km/h and no km/h less than the actual speed driven.
See regulation No 39 of the Economic Commission for Europe of the United Nations (UN/ECE): Point 5.4
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Useful information | FAQ | Tips and tricks

Tire calculator | Rim calculator | ET calculator - Tips and hints

What can the tire, rim & ET calculator do?

The calculator offers you an uncomplicated way to compare the dimensions of your current tires and rims with those of your desired tires and rims. Calculate precise values for rolling circumference, speed deviations, ground clearance and more. Determine the ideal ET value, calculate the tire diameter and find out which rim width is best suited to your vehicle. Our tire calculator provides you with a comprehensive analysis and a clear graphical representation.

It is a legal requirement that deviations remain within limits and that only approved combinations are used. Binding statements on tire sizes can be made by the TÜV, for example.

Which tires fit my vehicle?

Many drivers ask themselves this question, whether after changing their vehicle or out of interest in new tires, for example for a tuning project. There are many reasons to change the tire size: visual adjustments, improved driving characteristics or even a reduction in fuel consumption due to smaller rolling circumferences.

Important note: Changes to the rolling circumference should remain within the range of -2.5 % to +1.5 %, as larger deviations are often rejected by the TÜV. Our tire calculator shows you such differences and issues warnings for impermissible values.

Among other things, the rolling circumference influences the display of your speedometer. This may display a maximum of 10 % + 4 km/h more than the actual speed, but never less (see Regulation No 39 of the Economic Commission for Europe of the United Nations (UN/ECE): point 5.4). If an adjustment is necessary, this may result in additional workshop costs. Our tire calculator helps you to check such factors in advance.

The right tire size is crucial for the safety, comfort and performance of your vehicle. Our tire calculator will help you find the ideal tires for your car. Our tire calculator offers you an uncomplicated way to compare the dimensions of your current tires with those of your desired tires. It is a legal requirement that deviations remain within dimensions and that only approved combinations are used. However, only the TÜV can make binding statements on alternative tire sizes.

Why is the right tire size so important?

  • Security: Incorrect tires can lead to poor handling, longer braking distances and aquaplaning.
  • Comfort: The right tires ensure a comfortable ride and reduce driving noise.
  • Service: Tires influence factors such as acceleration, cornering behavior and fuel consumption.
  • Legality: It is important to comply with the legal regulations regarding tire size.
Visualize your new wheel/tire combination - quickly and easily!

With our tire, rim & ET calculator, choosing your new tires and rims is child's play. Thanks to the detailed 2D sketch, you can immediately see how the ratios and sizes of the desired wheel/tire combination will change.

It's as simple as that: Simply enter the data of your current tires and the desired dimensions of the new ones. Our system calculates everything for you and shows you the result in a clear graphic. Make a safe choice with our tire, rim & ET calculator!

Why you'll love our 2D sketch:

  • Simple and fast: No complicated technology - enter your values and off you go!
  • Precise results: You can see exactly what effect the changes have.
  • Clear presentation: All important information at a glance.

What you get visualized:

  • Size comparison: How big or small will your wheel / rim be?
  • Change in height and width: What is the effect of wider or narrower tires or rims?
  • Change in rolling circumference: Does the rolling circumference change when using the new dimensions?
  • Changes to the outer and inner rim edge: Does the desired rim move further outwards or inwards?
  • ...and many other details that will help you calculate your new tires or rims.

Notice: Our 2D sketch shows you the basic changes. Details such as the distance to the suspension strut, the brake system or the wheel arch may vary depending on the car model and are not included in the illustration.

Tire width, tire size, tire dimension: What do the values mean and where can they be found?

The tire width indicates how wide a tire is from one sidewall to the other and is specified in millimetres in the metric system. It has a direct influence on the vehicle's grip, ride comfort and handling.

To find the optimum tire size for your vehicle, you should observe the vehicle manufacturer's specifications. You will find the permitted tire sizes for your vehicle in the vehicle registration certificate or in the COC paper ("Certification of Conformity"). In principle, only tire/rim combinations listed in the respective approval document are permitted in the EU without further approval.

A tire size is specified in a combination of numbers and letters, for example 225/45 R17.

  • 225: This is the width of the tire in millimeters, measured from one sidewall to the other.
  • 45: This value indicates the ratio of the tire height to the width. In this example, the height is 45% d width.
  • R: The R stands for radial tires, which are most commonly used today.
  • 17: This is the diameter of the rim in inches on which the tire is mounted.

Advantages and disadvantages of wide and narrow tires

Wider tires:

  • Advantages: Better grip, shorter braking distances, more stable handling in curves
  • Disadvantages: Higher costs, increased fuel consumption, more driving noise, more susceptible to aquaplaning

Narrower tires:

  • Advantages: Less susceptible to aquaplaning, lower costs, quieter in operation
  • Disadvantages: Less grip, longer braking distances, more unstable handling

Which tires fit on which rims?

Which tire width is suitable for which rim width? This question often arises when buying new rims. We have created a table that shows you which tires fit which rims. This is based on the ETRTO (European Tire and Rim Technical Organization) formulas. The rim width is given in inches (as is usual for rim sizes), the tire widths in millimetres.

Table: Assignment of tire widths (mm) to rim widths (inches):

Rim width Min. tire width Recommended tire widths Max. Tire width
5 155 165 or 175 185
5.5 165 175 or 185 195
6 175 185 or 195 205
6.5 185 195 or 205 215
7 195 205 or 215 225
7.5 205 215 or 225 235
8 215 225 or 235 245
8.5 225 235 or 245 255
9 235 245 or 255 265
9.5 245 255 or 265 275
10 255 265 or 275 285
10.5 265 275 or 285 295
11 275 285 or 295 305
11.5 285 295 or 305 315
12 295 305 or 315 325
12.5 305 315 or 325 335
Rim, offset and spacers: All about the topic

The rim is not only the basis for the tire, but also has a significant influence on the appearance and driving characteristics of a vehicle. In addition to the diameter, which is specified in inches, the offset (ET value) is a decisive factor.

For example, an entry could read as follows: 8J x 18 ET34

Felgenmaße
8J is the rim width in inches, 18 is the rim diameter in inches and ET34 means that the distance between the center line of the rim and the contact circle of the rim is 34mm.

Offset (ET value)

This value indicates how far the center line of the rim is from the contact circle of the rim to the wheel hub. A high ET value means that the rim is offset further inwards, while a low ET value leads to a further outward deflection of the rim.

Why is the offset important?

  • Track widening / narrowing: The track width of the vehicle can be changed by selecting a rim with a different ET value.
  • Wheelbase: Changing the offset can also affect the wheelbase and thus change the handling.
  • Tire clearance: An incorrect offset can cause the tires to rub against the bodywork or stand in the wheel arch.

With the rim calculator above you can simulate and calculate the effects of different offset values on your vehicle. This allows you to determine the optimum offset for your desired setup.

Spacers:

  • What are wheel spacers? Wheel spacers are rings that are fitted between the wheel hub and the rim to widen the track width.
  • When are spacers needed? Wheel spacers are often used in conjunction with wider rims or for tuning measures.

Important notes: The use of wheel spacers must comply with the legal requirements and must not impair the function of the brake system and steering. With our wheel and tire calculator, you can easily calculate the required wheel spacer size to achieve a specific wheel spacing.

Individual vehicle features & approved combinations: You should pay attention to this when changing tires.

The Tire, Rim & ET Calculator is a helpful tool, but cannot take into account all individual vehicle characteristics. While it can help you calculate rolling circumference, speed deviations and other important values, certain vehicle-specific factors, such as brake disc size, cannot be taken into account. Changing from low sidewall tires and large diameter rims to high sidewall tires and low diameter rims may seem mathematically safe, but is often not advisable due to such factors. To ensure full compatibility, we strongly recommend that you consult a specialist when changing the tire diameter and rim diameter.

Only tire sizes approved for your vehicle can be calculated reliably. If tire sizes are not approved or have already been changed, there is a risk that the results will not be correct.

Important: Incorrect tire or rim sizes can lead to serious damage to the chassis, rims or tires and significantly impair driving safety. Always ensure that only compatible and approved wheel/tire combinations are used.

Seasonal tires, profile, age and more: A comprehensive overview

Choosing the right tires is crucial for safety and comfort when driving. In addition to the tire size, seasonal factors, tread, age and the tire load and speed index also play an important role.

Seasonal tires: It depends on the season

  • Summer tires: Optimized for dry and warm road conditions. They offer good grip and short braking distances at high temperatures.
  • Winter tires: Equipped with a special rubber compound and a tread pattern designed for snow and ice. They offer better traction on winter roads.
  • All-season tires: A compromise between summer and winter tires. They are suitable for use all year round, but do not offer the same performance as pure seasonal tires in extreme conditions.

Notice: Although all-season tires are a convenient solution, they can reach their limits in extreme winter conditions. In some regions with heavy snowfall, the use of winter-only tires is therefore recommended.

The tire tread: more than just a groove

The tire tread is crucial for grip on the road. It influences:

  • Water drainage: A good tread pattern ensures that water is drained away quickly and aquaplaning is prevented.
  • Traction: The tread depth and tread pattern influence grip on dry, wet and winter roads.
  • Braking distance: A worn tread significantly increases the braking distance.

Legal requirements: A minimum tread depth of 1.6 mm applies to car tires throughout the EU. If the tread falls below this depth, the tire is no longer safe and must be replaced.

Tire age: Even rubber gets old

Tires have an expiry date, even if they still have tread. Over time, the rubber compound hardens, which impairs the grip and service life of the tire. Experts recommend changing tires after ten years at the latest, regardless of the tread.

Tire load index and speed index: the right values for your vehicle

  • Tire load index: This indicates the maximum load a tire can carry. It is important to ensure that the vehicle's payload is not exceeded.
  • Speed index: This indicates the maximum speed for which a tire is designed. The speed index must at least correspond to the value specified in the vehicle documents.

Where can I find this information? The information on the tire load and speed index can be found on the sidewall of the tire.

Conclusion: The right choice of tires is crucial

Choosing the right tires is an investment in your safety and riding comfort. Pay attention to the seasonality, tread, age and appropriate indices. Have your tires checked regularly by a specialist and replace them if necessary.

Additional tips:

  • Tire pressure: Check the tire pressure regularly and keep it at the value recommended by the manufacturer.
  • Balancing: Have your wheels balanced regularly to avoid vibrations and uneven tire wear.
  • Storage: Store your tires in a cool, dry and dark place.
Load capacity index: Explanation & table

Load Index or also load capacity index or Load Index LI

The load index of a tire indicates how much weight an individual tire can carry at a certain air pressure. Any reduction in tire pressure reduces the load capacity of the tire. This index is essential to ensure that the tires can withstand the loads of the vehicle, especially when fully loaded.

The load index is indicated as a number on the tire sidewall, directly next to the tire dimension, e.g. 205/55 R16 91V. Here, the number 91 stands for a specific load value. To determine the exact load capacity, there is the following table in which the respective load index is assigned to a specific load capacity.

Table: Assignment of load index (LI) and load capacity (max. kg):

Load Index Max. kg Load Index Max. kg Load Index Max. kg Load Index Max. kg
20 80 21 82.5
22 85 23 87.5
24 90 25 92.5
26 95 27 97.5
28 100 29 103
30 106 31 109
32 112 33 115
34 118 35 121
36 125 37 128
38 132 39 136
40 140 41 145
42 150 43 155
44 160 45 165
46 170 47 175
48 180 49 185
50 190 51 195
52 200 53 206
54 212 55 218
56 224 57 230
58 236 59 243
60 250 61 257
62 265 63 272
64 280 65 290
66 300 67 307
68 315 69 325
70 335 71 345
72 355 73 365
74 375 75 387
76 400 77 412
78 425 79 437
80 450 81 462
82 475 83 487
84 500 85 515
86 530 87 545
88 560 89 580
90 600 91 615
92 630 93 650
94 670 95 690
96 710 97 730
98 750 99 775
100 800 101 825
102 850 103 875
104 900 105 925
106 950 107 975
108 1000 109 1030
110 1060 111 1090
112 1120 113 1150
114 1180 115 1210
116 1250 117 1300
118 1325 119 1400
Speed index: Explanation & table

Speed index GI or also speed index SI

The tire speed index indicates the maximum speed up to which a tire can be operated safely. The index is represented by a letter such as "H", "V" or "ZR", with each letter indicating a specific maximum speed. If this speed is exceeded, the tire can overheat and there is a risk of the tread separating from the carcass.

It is permitted to drive tires with a higher speed index than specified in the vehicle registration document, e.g. a "W" tire (270 km/h) instead of a "V" tire (240 km/h), as long as the tire is suitable for the required speed.

The speed index is indicated as a number on the tire sidewall, directly next to the tire dimension, e.g. 205/55 R16 91V. Here, the letter V stands for a specific speed index. In order to determine the maximum permissible speed for this tire, the following table is available, in which the respective speed index is assigned to a maximum speed in km/h.

Table: Assignment of speed index (speed index) and maximum tire speed:

Speed Index Max. km/h Speed Index Max. km/h Speed Index Max. km/h Speed Index Max. km/h
A1 5 A2 10
A3 15 A4 20
A5 25 A6 30
A7 35 A8 40
A9 45 B 50
C 60 D 65
E 70 F 80
G 90 J 100
K 110 L 120
M 130 N 140
P 150 Q 160
R 170 S 180
T 190 U 200
H 210 V 240
ZR 240+ W 270
Y 300
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Feedback
Tire diameter
Tire diameter:
Diameter of the tire.
Rolling circumference
Calculation incl. load from the vehicle and at a speed of approx. 60 km/h (tire circumference * 0.97).
Tire circumference
Purely calculated circumference of the tire without mounting on a rim and without load.
Tire height
Height of the sidewall of the tire.
Rim size
Rim size:
Diameter of the rim.
Rim width
Rim width:
Width of the rim.
Poke (Outer Edge)
Distance between the OUTER rim edge and the contact surface of the brake disk or brake drum.
Inset (Inner Edge)
Distance between the INNER rim edge and the contact surface of the brake disk or brake drum.
Change in ground clearance
Value by which the vehicle is higher or lower with the new tires.
Changing the rolling circumference. If the deviation is too high, it may be necessary to adjust the speedometer.
Displayed speedometer value with desired tires, which corresponds to the displayed 100 km/h with existing tires.
Change outer edge per side
Distance between the outer surfaces of the rims. The rims in the wheel housing move inwards or outwards by this value.
Change inside edge per side
Distance between the inner surfaces of the rims. The ET (offset) has an influence on this value.
Tire info
Tire info
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Rim info
Tire info
Tire info
Tire info
Tire info
Tire info
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