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Tyre size calculators, for calculating tyre sizes on metric, imperial and vintage tyres and converting sizes from one to the other.

Tyre size calculators

This page contains all the tyre size calculators and converters that are spread amongst the Wheel & Tyre Bible, all presented on a single page for quick reference.

The DOT Age Code Calculator

The calculation built in to this page is up-to-date based on today's date. If the DOT age code on your tyres is older than this code, change your tyres.

DOT AGE CODE:

Converting classic / vintage / imperial crossply tyre sizes to metric

This converter will turn your imperial tyre size into a metric tyre size:

Your imperial tyre size: x
Equivalent standard tyre size is :/100 R

Converting LT (Light Truck) imperial tyre sizes to metric

Your LT tyre size: xR
Equivalent standard tyre size is :/ R

Converting alpha numeric vintage tyre sizes to metric

This calculator will convert alpha numeric vintage tyre sizes into the closest metric tyre size. Remember the section width is only a close approximations between old load and new size these days:
C = 185    D = 195    E = 205    F = 215    G = 225    H = 235 etc.

Your alphanumeric tyre size: A B C D E F G HR /R

Converting Michelin PAX tyre sizes to metric

This calculator will convert Michelin PAX sizes into the closest metric tyre size.

Your PAX tyre size: /R /R

Comparing tyre sizes

This calculator will help you to compare two different tyre sizes to see the differences in rolling circumference, and any speedometer difference error between the two sizes.

Current wheel/tyre	New wheel/tyre
145 150 155 165 175 185 190 195 205 215 225 230 235 245 255 265 275 285 295 305 315 325 335 395 / 25 30 35 40 45 50 55 60 65 70 75 80 82 85 100 R 12 13 14 15 15.5 16 16.5 17 18 19 19.5 20 21 22 23 24 25 26	145 150 155 165 175 185 190 195 205 215 225 235 245 255 265 275 285 295 305 315 325 335 395 / 25 30 35 40 45 50 55 60 65 70 75 80 82 85 100 R 12 13 14 15 16 16.5 17 18 19 19.5 20 21 22 23 24 25 26
Current rolling circumference mm	New rolling circumference mm
Difference in circumference:mm or %
So when your speedo reads 70mph, you're actually travelling at mph

Comparing wheel offsets

This calculator will help you to understand how changing your wheel offset will affect the wheel's position in relation to your suspension and bodywork.

Current wheel/tyre	New wheel/tyre
Tyre Section: 145 155 165 175 185 190 195 205 215 225 230 235 245 255 265 275 285 295 305 315 325 335 395 Wheel offset: 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55	Tyre Section: 145 155 165 175 185 190 195 205 215 225 230 235 245 255 265 275 285 295 305 315 325 335 395 Wheel offset: 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55

Calculating ideal rim width for any given tyre size

This calculator will give you the ideal wheel rim size for any given tyre size.

Your tyre size: 145 155 165 175 185 195 205 215 225 230 235 245 255 265 275 285 295 305 315 325 335 / 30 35 40 45 50 55 60 65 70 75 80 85 R 12 13 14 15 15.5 16 16.5 17 18 19 19.5 20 21 22 23 x up to x