[68ragtop]

For some reason, I always thought that tires were measured across the tread surface, that hits the road, then the side wall height was the % of the first number. & of course rim diameter

245/60/15 for example. 245mm arcoss the tread, 60% of that number in sidewall height. Well, I was measuring for tire clearances, & to my surprise, the tread was much less than that. barely 225. The closest thing to 245 was the balooned out section of the side wall, but that was closer to 255.

so now I am guesing the top number is supposed to be the "overall width of the tire, with an added variable of rim thickness?

[wytnyt]

245 is the width of tire
60 is height of sidewall
15 is rim cir.
245 begins where edge of sidewall stops

[68ragtop]

So if that is true, a 245, might actually be a 255 or larger depending on the rim its mounted to. Yet a wider tire like a 265 on that same rim, might actually measure 265.

[wytnyt]

no
too narrow of a wheel will result in the tire being arc shaped
where if the rim is too wide the tire will be lower in the center of the tread,,,meaning tire contact is mostly at edges of tire
width of tire remains the same,,,just tilted in or outwards

[BILTIT]

Tire width DOES change with different width rims, not alot but it does change.

[wytnyt]

i disagree,,it doesnt change just less or more contacting the ground,,,depending on the width of rim

[BILTIT]

The tread section of the tire will only arc/flex so much, then the sidewall gets pushed/pulled out fo shape.

[68ragtop]

For sure the 245 measurement is not the tire tread width. That's what I found out yesterday.

This is where I got confused.

My 245's measure 220 across the widest point of the tread that could ever hit the road, These tires are on a an 8" wheel & balloon out to 260 at the widest point in the middle of the sidewall

[wytnyt]

yes i agree but the tread length is still the same ,,,its just arced one way or the other.
like if it were possible to put a 10 inch tire on a 4 inch wheel
you would only have 4 inches of tread touching the ground whereas the rest of the tread is trying to "act" like the sidewall
ive always been taught that for the best possible tire setup is to have your tire 10% less in width than the wheel.
as known all tires wear out on the edges when on the front of the vehicle.
using the 10%less ratio you compensate some for wear on the outsides of the tire.
whereas in the rear that isnt needed.
this is the reason tire rotations is recommended

[wytnyt]

this explains tire measuring.

Tire sizes express the tire’s various measurements in a standardized format written on the side of the tire, also called the sidewall. The three measurements included in all tire sizes are section width, aspect ratio, and diameter. Depending on their intended use, some tire sizes also include information such as speed rating.

Tire sizes are expressed in the format WWW/AAXDD. WWW is the tire’s section width, measured in millimeters. AA is the aspect ratio or profile of the tire, which expresses the tire’s height as a percentage of its width. X is a letter indicating the tire’s internal construction. DD is the diameter in inches of the wheel that the tire is intended to be mounted on. An example of a tire size written in this format is 225/50R16.

This particular tire has a section width of 225 millimeters (8.86 inches). Section width is measured from the widest point of the outer sidewall - the side with the tire sizes and brand name that faces out from the vehicle -[[[[[[ to the widest point of the inner sidewall when the tire is mounted on a specified width wheel.]]]]]]] Narrower tires have lower section width numbers.

The next number is the aspect ratio. Tire sizes separate the section width from the aspect ratio with a slash. This tire has an aspect ratio of 50, meaning that the profile, or sidewall height measured from wheel to tread, is 50% of the section width. This number is also called section height; the higher the number, the taller the sidewall.

Tire sizes include a letter following the section height that is not a measurement, but an identification of the tire’s internal construction. This “R” indicates radial construction, in which the tire’s body plies “radiate” outward from the wheel’s center. A “D” indicates plies that crisscross diagonally, used for light truck or spare tires. Tire sizes with a “B” are belted and nearly obsolete.

The final number in the tire size indicates the tire and wheel diameter to be used together - in this case, 16 inches. These inch rim sizes are used on most passenger vehicles, while some tires used on heavy-duty trucks or trailers use “half inch” sizes, e.g. 14.5. Some manufacturers carry tire sizes that express rim diameter in millimeters, or that include different dimensions for the inside and outside edges of the tire. These tire sizes are intended for use with specific vehicles and should not be combined with traditional tire sizes.

this explains why your measurements are coming up wrong
This particular tire has a section width of 225 millimeters (8.86 inches). Section width is measured from the widest point of the outer sidewall - the side with the tire sizes and brand name that faces out from the vehicle -[[[[[[ to the widest point of the inner sidewall when the tire is mounted on a specified width wheel.]]]]]]] Narrower tires have lower section width numbers.

[jnkgp]

you will also find that two tires from two different manufacterers will measure differently. The system seems to be only for reference, at least untill you get into the 18" and larger rim sizes.