Which tire is taller a 275/65/18 or a 255/70/18? i dont understand all the numbers.

 

The first number is width in mm.
the second number is the aspect ratio, a percentage of the width. It is the distance from rim to top of tire..
the last number is rim size in inches..

so, 275/65/18
275 * .65 = 178.75mm ................ Width times aspect ratio (percentage) looking from side of wheel, it's the tire above the rim.
178.75 * 2 = 357.5mm ................ You multiply by 2 because its the tire above and below the rim.

357.5/25.4 = 14.07inches. ................. 25.4mm = 1 inch.
14.07 inches + 18 inch rim = 32.07 inch tire

so..
275/65/18 = 32.07 inches tall
255/70/18 = 32.055 inches tall

the difference is that first number, the width.

275 = 10.8 inches of width
255 = 10.03 inches of width...

IT's a goofy cross of metric and standard....that make sense? I sometimes have issues with words, .....and clowns

 

Also, I don't know exactly how to measure the width of a tire.. I think every manufacturer has a different way. That is part of the reason why some tires don't measure what they should. Maybe inflation too. I hear a lot of people say their 35's measure 34, or something like that. Some tires are rightly marked in all standard.. 35x10x17.. so 35 inch tall, 10 inch wide 17 inch rim. Makes life easy.

 

Go to the mfg's website. They will have a specs sheet that will list the standard height and width of all of their tires.

Or open your favorite browser and search on "metric tire calculator" or "metric tire conversion", there are quite a few of these little programs out there that let you type in the metric size and convert it.

 

Discount Tire's website has a great little conversion tool and you can compare tires on there

 

Thanks for the help, it actully makes sense now!!