Reading tire sizes

Here is a small diagram I made to show you what the numbers on your tire mean . In this example, the tire says 225/40/18.. There can also be variants added into the code, like you might see 225/40/R 18 ZX (R stands for Radius, ZX represents random code as per tire manufacture for weight and speed rating) ...but this is the basics

I just posted this in Hanna's thread, but wanted to add this here as well just to clarify:


Actually I thought the second number (40) was the aspect ratio. Meaning that the sidewall height is 40% of the width of the tire.


225 multiplied by .40 equals 90 mm. Divide that by 25.4, and that gives you approximately 3.5 inches


EDIT: check this site out
http://www.miata.net/garage/tirecalc.html

It shows for a 225/40/18, that the sidewall is 3.5 inches. 40mm sidewall would be less than 2 inches.

Let's take a look:

Quote :

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.

Link: http://www.tirerack.com/tires/tiretech/techpage.jsp?techid=46

And more:
http://www.ehow.com/how_4764357_read-tire-measurements.html#ixzz1RWN2sty3
http://www.discounttire.com/dtcs/infoSidewall.do
http://www.tire-information-world.com/tire-markings.html

U mad bro? i see nothin wrong with my post lol

Chris' pic does say ratio for the 2nd number... lol


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Hannah that is true. However, the Linear dimension on the tire saying 40, suggests 40MM. ALTHOUGH, it does says MM for the first one, RATIO for the second one, and INCHES for the third one, so I really don't see why I thought it was wrong at first.

So even as a Mechanical Designer, even I can be wrong at first.

FYI - I'm not trying to be a rude/arrogant about this at all. I actually appreciate this, since so many people have asked me about this in the past.

SiRWannabe wrote:

U mad bro? i see nothin wrong with my post lol

Because you changed it...

Used to say "sidewall height/mm"

OOOOh, so I was fooled. LOL

Lol dont gotta be all defensive Q.. just havin fun.. yeah I was wrong.. but i think im about to do some tests.. besides only thing that was wrong about what I has was mm to ratio.. Never actually argued that it was mm i dont think?

either way i dont care as long as its semi relevant

xjoshx wrote:

either way i dont care as long as its semi relevant

:like:

btw.. Measured my sidewall today.. 35mm my tires are 215/35/18

SiRWannabe wrote:

btw.. Measured my sidewall today.. 35mm my tires are 215/35/18

that's what I said at first, mm for sidewall..

maroonCD5 wrote:

xjoshx wrote:

When people say tire sizes its like speaking another language to me.

it's easy:

width (mm)/sidewall (mm)/wheel diameter (in)

tire noobs