Posted on August 16, 2011.
tire sizes? What do the numbers on a tire? For example 235/75R-15.I know the R is radial and the 15 is the diameter of the rim, but 235? What is the height, it is the rim? 75.7 1 / 2 "? Please explain.Thanks!
Some people have approached it, no one got it right. Time for an expert.
Firstly, there must be the size of all there. This is not only the 235/75R15, you must include the full description: P235/75R15 105S.
The P indicates the tire is built using the Passenger "or" P-metric "system sizing, as opposed to the" Euro-metric "system calibration. Descriptions of each system are similar and dimensionally interchangeable, but the tires of the same size do not have the same load carrying capacity to the same inflation pressure. Both systems use load charts and inflation. Euro-metric tires do not have a "P" at the beginning of the description.
The 235 is the section width "of the tire in millimeters. The section width is the widest part of the tire (about halfway down the side), not the width of the tread. width of the tread is a different measure and can vary from one tire to another of the same size.
The 75 is the aspect ratio, which is represented as the relationship between height and width of the tire. The 75 means the tire bead to the tread is about 75% of 235mm in height.
The "R" means the tire is of radial construction - this is not the speed rating as it was erroneously posted above.
The "15" is of course the diameter of the wheel tire is designed to be mounted.
The "105" is the tire's Rating Service and provide the load carrying capacity of tires. The air in a tire is what carries the load of the vehicle. A tire is essentially a container for air. The more air, the higher the load the tire can carry (at one point). The maximum load a tire P235/75R15 105S can be at its maximum inflation pressure of 35 psi is 2.028 pounds. This information is molded on the tire sidewall.
The "S" (it could be other letters) to the end of the description is the speed of the Index of tires. This indicates the maximum speed at which the tire is certified to carry a load and there is a corresponding table to identify what the speed is for each letter. An "S" rated tire, for example, is certified to 112 mph.
Although not part of the size you might see a description as M + S, M / S or M & S on the sidewall near the description of magnitude. This indicates that the tire meets the RMA (Rubber Manufacturers Association) for use in mud and snow conditions. What it really means the tire is empty ration at least 34% (grooves) in the tread. This does not mean the tire will be of any use at all in the mud or snow in the real world and the tire may not yet be tested in such conditions.
Sorry if this was a little long but the tires are the # 1 point on a security vehicle. I suppose if someone cares to ask, they deserve an appropriate response.
ASE Certified Automotive Service Advisor with 5 years experience in the tire industry.
235/75R-15
235 is the width of the tire (not tread width)
75 is the aspect ratio (sidewall is 75% as large as the tire is wide)
R - radial
15 - diameter of the rim inside the tire
like a tire becomes lower aspect ratio, the tread becomes larger, so that a 195/60 will have a tread wider than a 195/70.
who care what this means, it has 15 inch tires, which is good for the fact that they are cheaper. Go to tirerack.com and they give you many choices of tires, look the best sellers for this size
235 - 75R - 15
235 is the tire width
75 is the height of fatigue (75% of 235)
R is in fact the speed rating of the tire
15 is the rim diameter
In this sample, 91 WM + S P205/55R16
Spacecraft P-passanger.
