Question:
What do the numbers mean on a tire?For instance 235/75R-15.I know the R is radial and the 15 is the rim diameter but 235?How tall it is off the rim?75,7 1/2"?Please explain.Thanks!
Answers:
First, let's put the whole size out there. It's not just the 235/75R15, you need to include the entire description: P235/75R15 105S.
The P means the tire is built using the "Passenger" or "P-Metric" sizing system, as opposed to the "Euro-Metric" sizing system. The descriptions for each system are similar and dimensionally interchangable but tires of the same size do not have the same load carrying capacity at the same inflation pressures. The two systems use different load and inflation tables. 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 (roughly half-way down the sidewall), not the width of the tread. Tread width is a different measurement and can vary from one tire to another in the same size.
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The 75 is the "aspect ratio" which is represented as the relationship between the height and the width of the tire. The 75 means the tire from bead to tread is approximately 75% of 235mm tall.
The "R" means the tire is of Radial construction - it is not the speed rating as was erroneously posted above.
The "15" is of course the wheel diameter the tire is designed to be mounted on.
The "105" is the Service Rating of the tire and gives the tires load carrying capacity. The air in a tire is what carries the load of the vehicle. A tire is basically a container for that air. The more air, the bigger the load the tire can carry (to a point). The maximum load a P235/75R15 105S tire can carry at its maximum inflation pressure of 35 psi is 2,028 lbs. This information is molded on to the tires sidewall.
The "S" (it could be other letters as well) at the end of the description is the Speed Rating of the tire. 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.
Though not part of the size you might see a description like M+S, M/S or M&S on the sidewall near the size description. This indicates the tire meets the RMA (Rubber Manufacturers Association) standards for use in mud and snow conditions. What it really means is the tire has at least 34% void ration (grooves) in the tread. It doesn't mean the tire will be of any use at all in mud or snow in the real world and the tire may not have even been tested in such conditions.
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Sorry if that got a little long but tires are the #1 safety item on a vehicle. I figure if someone cares enough to ask, they deserve a proper answer.
ASE Certified Automotive Service Advisor with 5 years experience in the tire industry.
I could be wrong but 235 means the width and 75 is the height.
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235/75R-15What would be the best way to clean up your car? So there is no dust, mud, and car hair,etc??
235 is the width of the tire (not width of tread)
75 is the aspect ratio (sidewall is 75% as tall as tire is wide)
R - radial
15 - diameter of rim, inside of tire
as a tire gets lower aspect ratio, the tread gets wider, so a 195/60 will have a wider tread than a 195/70.
who care what it means, it a 15 inch tires, which is good for the fact they are cheaper. go to tirerack.com and they give you alot of choice of tires, look at the best sellers for that size
235 - 75r - 15
235 is the tire width
75 is the tired height (75% of the 235)
r is actually the speed rating of the tire
15 is the rim size
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in this example P205/55R16 91 W M+SP-passanger vehicle 205-section width mm. (part of tire touching pavement) 55- height / width R-Radial 16- rim diameter 91W- speed rating M+S Good for Mud and Snow
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