Uniform Tire Quality Grade (UTQG) Labeling
Treadware: a measurement of tread durability with a reference standard of 100. 200 would mean twice the standard.
Traction: the measurement of a tire's ability to stop on wet test surfaces&of asphalt and concrete under controlled conditions.

Traction Grades:
A: performed well on both surfaces
B: performed well on at least one of the surfaces
C: performed poorly on one or both of the surfaces.
Temp. Resistance Grades:
A: The tire withstood a 30mn run at 115 mph w/o failing.
B: The tire passed 100 mph but not 115 mph.
C: The tire failed to complete a half-hour at 100 mph (uuh, is it a Hot Wheels?).

Following the Department of Transportation, or DOT label, on the tire's sidewall is: the serial number of the tire manufacturer, manufacturing plant, tire size, and date of manufacture. Federal law requires that tire dealers record the DOT identification numbers along with the tire buyer's name and address. There may be a service description on the end of the size of a 2-digit load index and a speed rating letter.

US tire-speed rating is based on laboratory testing conditions;
European rating is based on actual road testing.
High-performance tires are rated S or greater and aspect ratios of 70
or less (typically less than 60). Conventional radials meet the minimum DOT standard of 85mph.
Speed symbols may currently be marked on a tire in one of three ways: 205/60ZR15; 205/60ZR15 89W; or 205/60R15 89W.

Aspect ratio is determined by dividing a tire's section height by its section width when the tire is inflated to maximum air pressure, mounted on the approved measuring rim, and under no load. The shorter the sidewall, or lower the aspect ratio, the quicker the response from steering wheel to tire. Also, a low ratio means a wider tread contact area which reduces distortion, provides improved cornering, and usually gives a stiffer feel to the ride.

175/60 R 14 75H

175 is the width in mm of the tyre tread (could be 100 up to 325 for ultra-sporty tyres)

60 is the aspect ratio in percent. In this case the tyre height (from rim to tread) is 60 percent of the width (which is 175mm). That works out as 105mm. Not normally higher than 82, and can go as low as 30 for ultra-sport tyres. "low profile" means an aspect ratio below about 60 percent

R means radial construction. The alternative is Cross-ply or bias ply

14 is the rim diameter in inches. A very small car runs on 12-inch rims, big sports cars use 18, 19, or even 20-inch rims to make maximum space for big brakes. The biggest specialist rims are now 22 inches--as big as a truck tyre rim!

75 is the Load Index and indicates the maximum load that should be applied to the tyre when driven at maximum speed. In this case 75 means 387 kg. For all but heavy trucks, this is not usually a problem, but you can find load ratings here: http://www.tyres-online.co.uk/techinfo/load_indices.asp

H is the speed rating. This is the maximum speed the tyre should ever be driven. This is the area where you have most choice. Higher speed ratings mean higher prices, and often, shorter life.

N 140 kph / 87 mph P 150kph / 93 mph Q 160 kph /99 mph R 170 kph / 106 mph S 180 kph / 112 mph T 190 kph / 118 mph H 210 kph / 130 mph V 240 kph / 149 mph W 270 kph / 168 mph Y 300 kph / 186 mph Z over 300 kph

other marking include M+S for Mud and Snow (winter tyres)

Ever wondered what those numbers were on the side of your tires, something like P235/75R17 or more commonly, P205/75R15, or as large as P315/45R17, so many combinations.

The numbers on the side of your tire, apart from various others, is a sequence or coding which defines what the size, shape, and height of your tire is. Here they are broken down:

Tire Type (P):
Tire Type refers to the tire that the vehicle is intended for. P for a passenger car, some others include: LT for a light truck, and T for a temporary or spare tire.

Tire Width (235):
Tire Width refers to the size of the tire from sidewall to sidewall in millimeters (mm). Since the width of the tire can be affected by the rim size, the measurement is taken while it's on it's intended rim.

Aspect Ratio (75):
Aspect Ratio is the height of the tire in relation to the width of the tire as express in percentage. For example: if a tire was 205mm wide, and the aspect ratio was 75%: The height of the tire would be 153.75mm from the bottom of the tire to the outside of the rim. High performance tires usually have lower aspect ratios (around 35 to 40%). This is because lower aspect ratios have better lateral stability for better cornering ability. Many people buy wider tires with a small aspect ratio with the intention of receiving better straight-line traction, and realize that it's not what they expected.

Tire Construction (R):
Tire Construction is denoted by one of three letters on the tire. The current method is radial construction for radial tires and is denoted by an R. Older methods were diagonal bias (D) or bias belted (B).

Rim Size (17):
Rim Size is the size of the rim that the tire is designed to fit on, it won't fit properly on anything else. This number is expressed in inches.

So there you have it, a P235/75R17 is a 235mm radial passenger tire with an aspect ratio of 75% designed for a 17" rim. It's probably best sticking with a rim/tire combination that results in a configuration that's no taller but no shorter than your original combination. changing to tires which are a lot taller/shorter will throw your speedometer off.

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