tyre markings?

Question

what does the numbers on the tyre wall refer to??

the for example 185/55 R15

what is the low profile? the compound? size??

Answer 1

If the description starts with a "P" (ex: P185/55R15 81V) then the tire was built to "Passenger-Metric" (American) standard. No P means the tire uses the Euro-Metric sizing system. Dimensionally interchangable the two systems have different load carrying capacities at different pressures.

"185" is the "section width" or the width of the tire at its widest point in milimeters. This is not the width of the tread.

"55" is the aspect ratio, or the height of the tire from the bead (where it mounts to the wheel) to the top of the tread measured as a percentage of the section width. In other words, your tire is 55% of 185mm tall.

R means the tire is of Radial construction

15 means it is for installation of a rim of 15 inches diameter.

The next set of numbers, which you ignored but are still part of the size and crucially important is the "Service Description" or "Load Index" and tells us how much weight the tire can carry. In this size that number might be 81 or 82 signifying maximum load capacities of 1,019 lb and 1,047 lb at 36 psi respectively. That number is followed by a letter which is the tires "Speed Rating" or the maximum sustained speed the tire is designed to take. In a size like this the letter will typically be an "H" (up to 210 kmh) or "V" (up to 240 kmh) but there are many other possible speed ratings as well.

The complete tire size then would then read something like this:

185/55R15 82V

Answer 2

185 is the size of the tire. 55 is the aspect ratio. 15 is the wheel diameter. Go to tirerack.com on the net for a complete detailed explanation concerning the aspect ratio.
Very briefly it's the ratio of the distance between the bead of the tyre and the distance to the tread. The lower the aspect ratio the less distance between the bead (tire rim) and the tread. As we call it, short narrow sidewall tyres.

Answer 3

size