Tire Size Confusion

[Honest_Bob]

I think I've been very confused on what the numbers mean.

235/75-15

I thought 235 was the width of the tire, but was told otherwise at work yesterday. Can someone explain what all the numbers mean? :(

[gary]

Straight from tire rack... http://www.tirerack.com/tires/tiretech/techpage.jsp?techid=46

Section Width

Following the letter(s) that identify the type of vehicle and/or type of service for which the tire was designed, the three-digit numeric portion identifies the tire's "Section Width" (cross section) in millimeters.

P225/50R16 91S

The 225 indicates this tire is 225 millimeters across from the widest point of its outer sidewall to the widest point of its inner sidewall when mounted and measured on a specified width wheel. This measurement is also referred to as the tire's section width. Because many people think of measurements in inches, the 225mm can be converted to inches by dividing the section width in millimeters by 25.4 (the number of millimeters per inch).

225mm ¿ 25.4 = 8.86"

Sidewall Aspect Ratio

Typically following the three digits identifying the tire's Section Width in millimeters is a two-digit number that identifies the tire's profile or aspect ratio.

P225/50R16 91S

The 50 indicates that this tire size's sidewall height (from rim to tread) is 50% of its section width. The measurement is the tire's section height, and also referred to as the tire's series, profile or aspect ratio. The higher the number, the taller the sidewall; the lower the number, the lower the sidewall. We know that this tire size's section width is 225mm and that its section height is 50% of 225mm. By converting the 225mm to inches (225 ¿ 25.4 = 8.86") and multiplying it by 50% (.50) we confirm that this tire size results in a tire section height of 4.43". If this tire were a P225/70R16 size, our calculation would confirm that the size would result in a section height of 6.20", approximately a 1.8-inch taller sidewall.

[piknockout]

Question answered above. Someone at your work doesn't know $hit. ;)

[1988 Olds]

Yeah, I had people at the tire store try and tell me once a 255 was no wider then a 235 cause thats all they had in stock. I got the tires somewhere else, went back to the store and got the guy outside and asked him which tires on my car were wider. He said the backs, and I told him to go read the side to prove to him the number means width.

[Honest_Bob]

Haha, thanks guys, it seems to be a common misconseption since that was the second guy that was trying to tell me the same thing. I thought I was wrong. :)