Tyre Upsize Calculator
How to Calculate Tire Size
Calculating tire size involves understanding the various measurements provided on a tire’s sidewall. Here’s a step-by-step guide:
- Width: Look for the section width, which is the width of the tire in millimeters from sidewall to sidewall.
- Aspect Ratio: Find the aspect ratio, which is the ratio of the height of the tire’s sidewall to its width. It’s represented as a percentage.
- Construction: Determine the tire construction type. Most passenger tires are “R” for radial construction.
- Rim Diameter: Note the rim diameter, which is the diameter of the wheel’s rim in inches.
Once you have these measurements, you can express the tire size in a standard format, typically written as: Width / Aspect Ratio R Rim Diameter.
For example, if your tire has the following measurements:
- Width: 215mm
- Aspect Ratio: 60%
- Construction: Radial (R)
- Rim Diameter: 16 inches
Your tire size would be: 215/60R16.
Additionally, to calculate the overall diameter of the tire (important for speedometer calibration and fitment), you can use this formula:
Overall Diameter = (Width * Aspect Ratio / 100) * 2 + Rim Diameter (in inches)
For example, using the above measurements:
Overall Diameter = (215 * 60 / 100) * 2 + 16
Overall Diameter ≈ 25.15 inches.
How to Calculate Sidewall Height
Calculating sidewall height involves using the aspect ratio of the tire. Here’s how to do it:
- Determine Aspect Ratio: The aspect ratio is given as a percentage on the tire’s sidewall. It represents the height of the sidewall as a percentage of the tire’s width.
- Calculate Sidewall Height: To find the sidewall height, multiply the tire’s width by the aspect ratio and then divide by 100.
Mathematically, it’s expressed as:
Sidewall Height = (Tire Width * Aspect Ratio) / 100
For example, let’s say you have a tire with the following specifications:
- Tire Width: 215 mm
- Aspect Ratio: 60%
To calculate the sidewall height:
Sidewall Height = (215 * 60) / 100 Sidewall Height = 129 mm
So, the sidewall height of this tire would be 129 millimeters.
How to Calculate Revolutions Per Mile
To calculate revolutions per mile, you need to know the circumference of the tire. Here’s how you can calculate it:
- Find the Circumference of the Tire: The circumference of the tire is the distance it covers in one revolution. It’s calculated using the formula:
Circumference = 2 * π * (Rim Diameter / 2 + Sidewall Height)
Where:
- Rim Diameter is the diameter of the wheel’s rim in inches.
- Sidewall Height is the height of the tire’s sidewall in inches.
- Convert Circumference to Miles: Since you want revolutions per mile, you need to convert the circumference to miles. There are 63,360 inches in a mile, so divide the circumference by 63,360 to get the distance covered by one revolution in miles.
- Calculate Revolutions Per Mile: Once you have the distance covered by one revolution in miles, take the reciprocal to find the number of revolutions per mile.
Here’s the formula to calculate revolutions per mile:
Revolutions Per Mile = 1 / (Circumference in miles)
For example, let’s say you have a tire with the following specifications:
- Rim Diameter: 16 inches
- Sidewall Height: 5 inches
First, find the circumference:
Circumference = 2 * π * (16 / 2 + 5) Circumference ≈ 85.94 inches
Next, convert the circumference to miles:
Circumference in miles ≈ 85.94 / 63,360 ≈ 0.001355 miles
Finally, calculate revolutions per mile:
Revolutions Per Mile ≈ 1 / 0.001355 ≈ 737.28
So, the tire makes approximately 737.28 revolutions per mile.
How to Read Tire Size
Reading tire size might seem complicated at first, but it’s straightforward once you understand the format. Here’s a breakdown:
- Width: The first number represents the width of the tire in millimeters, measured from sidewall to sidewall when the tire is mounted and inflated to the recommended pressure.
- Aspect Ratio: The aspect ratio, represented by a two-digit number, indicates the height of the tire’s sidewall as a percentage of its width. For example, an aspect ratio of 60 means the sidewall height is 60% of the tire’s width.
- Construction Type: The construction type specifies how the tire is built. Most passenger car tires have a radial construction, indicated by the letter “R” in the size.
- Rim Diameter: The rim diameter, represented by a two-digit number, indicates the diameter of the wheel rim in inches. It’s the diameter of the wheel onto which the tire will be mounted.
- Load Index and Speed Rating: Sometimes, the tire size may also include load index and speed rating symbols. These indicate the maximum load capacity and speed at which the tire can safely operate. For example, “91V” means a load index of 91 and a speed rating of V.
Putting it all together, a tire size might look like this: 215/60R16.
- 215 is the width of the tire in millimeters.
- 60 is the aspect ratio, indicating the sidewall height as a percentage of the tire’s width.
- R signifies radial construction.
- 16 is the rim diameter in inches.
So, in this example, the tire is 215 millimeters wide with a sidewall height that is 60% of the width, it has a radial construction, and it’s designed to fit a 16-inch wheel rim.
What Do the Tire Size Numbers Mean?
The numbers in a tire size represent different aspects of the tire’s dimensions and characteristics. Here’s what each number signifies:
- Width: The first number indicates the width of the tire in millimeters. It’s the measurement from sidewall to sidewall when the tire is mounted and inflated to the recommended pressure. For example, in a tire size like 215/60R16, “215” represents the tire width.
- Aspect Ratio: The aspect ratio is represented by a two-digit number and indicates the height of the tire’s sidewall as a percentage of its width. For instance, in the same tire size 215/60R16, “60” is the aspect ratio, indicating that the sidewall height is 60% of the tire’s width.
- Construction Type: The construction type denotes how the tire is built. Most passenger car tires use radial construction, which is indicated by the letter “R” in the tire size. Radial tires have plies that run radially from the center of the tire to the edges.
- Rim Diameter: The last number in the tire size represents the diameter of the wheel rim in inches. It indicates the size of the wheel onto which the tire will be mounted. In the tire size 215/60R16, “16” denotes that the tire is designed to fit a 16-inch wheel rim.
- Load Index and Speed Rating: Sometimes, the tire size may also include load index and speed rating symbols. These indicate the maximum load capacity and speed at which the tire can safely operate. For example, a tire with a size of 215/60R16 might also have a load index of 91 and a speed rating of V, which means it can carry a maximum load specified for 91 and operate safely at speeds up to the speed rating of V.
Tire Size Chart
| Tire Size | Section Width (Tread Width) | Tire Height (Diameter) |
|---|---|---|
| 15-inch rims | ||
| 205/70R15 | 8″ | 26.3″ |
| 215/75R15 | 8.46″ | 27.7″ |
| 235/75R15 | 9.25″ | 28.9″ |
| 255/70R15 | 10″ | 29.1″ |
| 265/70R15 | 10.4″ | 29.6″ |
| 16-inch rims | ||
| 225/75R16 | 8.8″ | 29.3″ |
| 235/85R16 | 9.25″ | 31.7″ |
| 245/75R16 | 9.6″ | 30.5″ |
| 265/70R16 | 10.4″ | 30.6″ |
| 265/75R16 | 10.4″ | 31.6″ |
| 285/75R16 | 11.2″ | 32.8″ |
| 305/70R16 | 12″ | 32.8″ |
| 315/75R16 | 12.4″ | 34.6″ |
| 345/75R16 | 13.6″ | 36.4″ |
| 17-inch rims | ||
| 235/65R17 | 9.25″ | 29″ |
| 245/70R17 | 9.6″ | 30.5″ |
| 255/75R17 | 10″ | 32″ |
| 255/80R17 | 10″ | 33″ |
| 265/70R17 | 10.4″ | 31.6″ |
| 275/70R17 | 10.8″ | 32.2″ |
| 285/70R17 | 11.2″ | 32.7″ |
| 285/75R17 | 11.2″ | 33.8″ |
| 305/65R17 | 12″ | 32.6″ |
| 315/70R17 | 12.4″ | 34.4″ |
| 335/35R17 | 13.2″ | 26.25″ |
| 18-inch rims | ||
| 265/60R18 | 10.4″ | 30.5″ |
| 275/65R18 | 10.8″ | 32.1″ |
| 275/70R18 | 10.8″ | 33.2″ |
| 285/75R18 | 11.2″ | 34.8″ |
| 295/65R18 | 12.6″ | 33.1″ |
| 305/60R18 | 12″ | 32.4″ |
| 305/70R18 | 12″ | 34.8″ |
| 20-inch rims | ||
| 275/60R20 | 10.8″ | 33″ |
| 275/65R20 | 10.8″ | 34″ |
| 285/60R20 | 11.2″ | 33.4″ |
| 285/65R20 | 11.2″ | 34.5″ |
| 295/55R20 | 12.6″ | 32.8″ |
| 295/60R20 | 11.6″ | 33.9″ |
| 305/55R20 | 12″ | 33.2″ |
| 325/60R20 | 12.8″ | 35.3″ |
| 345/30R20 | 13.6″ | 28.2″ |
Tyre size explained
Tyre Dimensions:
Width:
This is the section width of your tyre. It’s measured in millimeters from one inner sidewall to the opposite outer sidewall. For example, a width of 195mm.
Aspect Ratio:
The aspect ratio indicates the height of your tyre’s sidewall as a percentage of its width. Lower profile tyres have smaller aspect ratios. For instance, if the height of the tyre is 65% of its width.
Tyre Construction:
This denotes the method used to construct your tyre. For example, “R” for radial ply construction, which is the most common method for passenger tyres.
Rim: The rim diameter refers to the size of the wheel rim in inches. If you’re purchasing wheels for existing tyres, you’ll need to match the rim size. For instance, a rim size of 15 inches.
Load Index and Speed Symbol:
These figures show the tire’s safe load and speed. It must be in good condition, fitted correctly, and inflated to the right pressure. For example, a load index of 91 and a speed symbol of V.
Tyre speed rating chart
Tyre speed symbol table
| Speed Symbol | Rating (Km/h) |
| 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 |
| W | 270 |
| Y | 300 |
| Z | 240+ |
Tyre load rating chart
Tyre load index table
Load shows the max safe weight for a tire. It must be in good condition, properly fitted, and at the right pressure. Look at the table below for the load index and max weight per tire.
| Load Index | Max Load (kg) | Load Index | Max Load (kg) | Load Index | Max Load (kg) | Load Index | Max Load (kg) | Load Index | Max Load (kg) | Load Index | Max Load (kg) |
|---|---|---|---|---|---|---|---|---|---|---|---|
| 60 | 250 | 85 | 515 | 110 | 1060 | 135 | 2180 | 160 | 4500 | 185 | 9250 |
| 61 | 257 | 86 | 530 | 111 | 1090 | 136 | 2240 | 161 | 4625 | 186 | 9500 |
| 62 | 265 | 87 | 545 | 112 | 1120 | 137 | 2300 | 162 | 4750 | 187 | 9750 |
| 63 | 272 | 88 | 560 | 113 | 1150 | 138 | 2360 | 163 | 4875 | 188 | 10000 |
| 64 | 280 | 89 | 580 | 114 | 1180 | 139 | 2430 | 164 | 5000 | 189 | 10300 |
| 65 | 290 | 90 | 600 | 115 | 1215 | 140 | 2500 | 165 | 5150 | 190 | 10600 |
| 66 | 300 | 91 | 615 | 116 | 1250 | 141 | 2575 | 166 | 5300 | 191 | 10900 |
| 67 | 307 | 92 | 630 | 117 | 1285 | 142 | 2650 | 167 | 5450 | 192 | 11200 |
| 68 | 315 | 93 | 650 | 118 | 1320 | 143 | 2725 | 168 | 5600 | 193 | 11500 |
| 69 | 325 | 94 | 670 | 119 | 1360 | 144 | 2800 | 169 | 5800 | 194 | 11800 |
| 70 | 335 | 95 | 690 | 120 | 1400 | 145 | 2900 | 170 | 6000 | 195 | 12150 |
| 71 | 345 | 96 | 710 | 121 | 1450 | 146 | 3000 | 171 | 6150 | 196 | 12500 |
| 72 | 355 | 97 | 730 | 122 | 1500 | 147 | 3075 | 172 | 6300 | 197 | 12850 |
| 73 | 365 | 98 | 750 | 123 | 1550 | 148 | 3150 | 173 | 6500 | 198 | 13200 |
| 74 | 375 | 99 | 775 | 124 | 1600 | 149 | 3250 | 174 | 6700 | 199 | 13600 |
| 75 | 387 | 100 | 800 | 125 | 1650 | 150 | 3350 | 175 | 6900 | 200 | 14000 |
| 76 | 400 | 101 | 825 | 126 | 1700 | 151 | 3450 | 176 | 7100 | 201 | 14500 |
| 77 | 412 | 102 | 850 | 127 | 1750 | 152 | 3550 | 177 | 7300 | 202 | 15000 |
| 79 | 437 | 104 | 900 | 129 | 1850 | 154 | 3750 | 179 | 7750 | 204 | 16000 |
| 80 | 450 | 105 | 925 | 130 | 1900 | 155 | 3875 | 180 | 8000 | 205 | 16500 |
| 81 | 462 | 106 | 950 | 131 | 1950 | 156 | 4000 | 181 | 8250 | 206 | 17000 |
| 82 | 475 | 107 | 975 | 132 | 2000 | 157 | 4125 | 182 | 8500 | 207 | 17500 |
| 83 | 487 | 108 | 1000 | 133 | 2060 | 158 | 4250 | 183 | 8750 | 208 | 18000 |
| 84 | 500 | 109 | 1030 | 134 | 2120 | 159 | 4375 | 184 | 9000 | 209 | 18500 |
Examples:
RFT – Run Flat Technology
MOE – Mercedes Original Equipment
LRR – Low Rolling Resistance
RBT – Raised Black Letters Tubeless
OWT – Outline White Letters Tubeless
RWT – Raised White Letters Tubeless
LWT – Line White Tubeless
TT – Tube Type
TL – Tubeless
XL – Extra Load
LT – Light Truck construction
N* – Porsche specification
☆ – BMW spec