polishmafia
02-16-2009, 07:39 PM
Over the last couple of weeks, I've had a few PMs asking about tires. I thought I should do a quick write-up on how to read your tires and what the information on them means.
Tire Size
On every tire, the size is written is in a three part format.
For example, alot of stock Mitsus come with the tire size 205 55 16.
Part 1 - 205 - This is the width of the tread, in millimeters.
Moving to a 215 tire means the tread is 10 millimeters wider than a 205.
Part 2 - 55 - This is the aspect ratio
This equals the sidewall height, in aspect to the width of the tire. In this example, the sidewall height is 55% of the tire's width.
Part 3 - 16 - This, in inches, is the rim diameter.
If you are thinking about getting a set of tires that are not the stock size, you can use a few online tire calculators to get information about the new size versus the old size. Here are a couple links.
http://www.1010tires.com/tiresizecalculator.asp
http://www.tiresizecalculator.info/
http://www.miata.net/garage/tirecalc.html
Load Index and Speed Index
Normally, after the tire size, are a couple of other numbers. This is the tire's load and speed rating.
The first number is the Load Index. The load rating basically means, per tire, what that tire is rated for weight.
Please refer to this chart of tirerack.com for specific ratings.
http://www.tirerack.com/tires/tiretech/techpage.jsp?techid=35
The second number is the speed index. This is the (recommended) maximum speed that this tire should ever travel at. We all know here that none of us ever go over the posted speed limit ;), but this is good information to know.
M - 81 mph
N - 87 mph
P - 93 mph
Q - 99 mph
R - 106 mph
S - 112 mph
T - 118 mph
U - 124 mph
H - 130 mph
V - 149 mph
DOT Codes
On every tire sold in the US is a set of number and letters (up to 12 characters in length).
For example MT1B 18HR 4808
The first two sets of characters are codes that denote the manufacturer of tire, and the plant is was made in.
The third set of characters can be very important when purchasing new tires. The third set of characters will always be numbers. This is the week of the year and the year the tire was manufactured.
4808 means the tire was manufactured during the 48th week of 2008.
Prior to 2000, some DOT codes just ended with one number. 349 would mean the tire was manufactured during the 34th week of 1999.
Before buying a set of tires, any reputable shop will let you look at the DOT codes before you purchase them.
Arguments about buying a tire that was constructed more than a couple of years ago go both ways. Some people state that older tires have no problems, while others say that older tires may be brittle. I personally agree with the latter. I would not purchase a tire that is a couple of years old and never mounted.
UTQG
This stands for Uniform Tire Quality Grading, which is a rating system developed by the Department of Transportation.
The following is taken from Goodyear.com
Tread Wear
More Than 100 - Better
100 - Baseline
Less Than 100 - Poorer
The tread wear grade is a comparative rating based on the wear rate of the tire when tested under controlled conditions on a specified government test track. A tire graded 200 would wear twice as long on the government test track as one graded 100. Your actual tire mileage depends upon the conditions of their use and may vary due to driving habits, service practices, differences in road characteristics and climate. Note: Tread wear grades are valid only for comparisons within a manufacturer's product line. They are not valid for comparisons between manufacturers.
Traction
A - Best
B - Intermediate
C - Acceptable
Traction grades represent the tire's ability to stop on wet pavement as measured under controlled conditions on specified government test surfaces of asphalt and concrete. The Traction grade is based upon "straight ahead" braking tests; it does not indicate cornering ability.
Temperature
A - Best
B - Intermediate
C - Acceptable
The temperature grades represent the tire's resistance to the generation of heat when tested under controlled conditions on a specified indoor laboratory test wheel. Sustained high temperatures can cause the materials of the tire to degenerate and thus reduce tire life. Excessive temperatures can lead to tire failure. Federal law requires that all tires meet at least the minimal requirements of Grade C.
Maximum Tire Pressure
Lastly, just because I get alot of questions about this at the shop, this is the maximum tire pressure rated for the tire. This is not the pressure the tire is supposed to be normally inflated to. This is the maximum pressure that the tire can safely hold.
On most vehicles, the recommended tire pressure for a vehicle is listed on a sticker in the driver's door jam, or can be found in the vehicle's owner's manual.
Any questions, feel free to ask.
Tire Size
On every tire, the size is written is in a three part format.
For example, alot of stock Mitsus come with the tire size 205 55 16.
Part 1 - 205 - This is the width of the tread, in millimeters.
Moving to a 215 tire means the tread is 10 millimeters wider than a 205.
Part 2 - 55 - This is the aspect ratio
This equals the sidewall height, in aspect to the width of the tire. In this example, the sidewall height is 55% of the tire's width.
Part 3 - 16 - This, in inches, is the rim diameter.
If you are thinking about getting a set of tires that are not the stock size, you can use a few online tire calculators to get information about the new size versus the old size. Here are a couple links.
http://www.1010tires.com/tiresizecalculator.asp
http://www.tiresizecalculator.info/
http://www.miata.net/garage/tirecalc.html
Load Index and Speed Index
Normally, after the tire size, are a couple of other numbers. This is the tire's load and speed rating.
The first number is the Load Index. The load rating basically means, per tire, what that tire is rated for weight.
Please refer to this chart of tirerack.com for specific ratings.
http://www.tirerack.com/tires/tiretech/techpage.jsp?techid=35
The second number is the speed index. This is the (recommended) maximum speed that this tire should ever travel at. We all know here that none of us ever go over the posted speed limit ;), but this is good information to know.
M - 81 mph
N - 87 mph
P - 93 mph
Q - 99 mph
R - 106 mph
S - 112 mph
T - 118 mph
U - 124 mph
H - 130 mph
V - 149 mph
DOT Codes
On every tire sold in the US is a set of number and letters (up to 12 characters in length).
For example MT1B 18HR 4808
The first two sets of characters are codes that denote the manufacturer of tire, and the plant is was made in.
The third set of characters can be very important when purchasing new tires. The third set of characters will always be numbers. This is the week of the year and the year the tire was manufactured.
4808 means the tire was manufactured during the 48th week of 2008.
Prior to 2000, some DOT codes just ended with one number. 349 would mean the tire was manufactured during the 34th week of 1999.
Before buying a set of tires, any reputable shop will let you look at the DOT codes before you purchase them.
Arguments about buying a tire that was constructed more than a couple of years ago go both ways. Some people state that older tires have no problems, while others say that older tires may be brittle. I personally agree with the latter. I would not purchase a tire that is a couple of years old and never mounted.
UTQG
This stands for Uniform Tire Quality Grading, which is a rating system developed by the Department of Transportation.
The following is taken from Goodyear.com
Tread Wear
More Than 100 - Better
100 - Baseline
Less Than 100 - Poorer
The tread wear grade is a comparative rating based on the wear rate of the tire when tested under controlled conditions on a specified government test track. A tire graded 200 would wear twice as long on the government test track as one graded 100. Your actual tire mileage depends upon the conditions of their use and may vary due to driving habits, service practices, differences in road characteristics and climate. Note: Tread wear grades are valid only for comparisons within a manufacturer's product line. They are not valid for comparisons between manufacturers.
Traction
A - Best
B - Intermediate
C - Acceptable
Traction grades represent the tire's ability to stop on wet pavement as measured under controlled conditions on specified government test surfaces of asphalt and concrete. The Traction grade is based upon "straight ahead" braking tests; it does not indicate cornering ability.
Temperature
A - Best
B - Intermediate
C - Acceptable
The temperature grades represent the tire's resistance to the generation of heat when tested under controlled conditions on a specified indoor laboratory test wheel. Sustained high temperatures can cause the materials of the tire to degenerate and thus reduce tire life. Excessive temperatures can lead to tire failure. Federal law requires that all tires meet at least the minimal requirements of Grade C.
Maximum Tire Pressure
Lastly, just because I get alot of questions about this at the shop, this is the maximum tire pressure rated for the tire. This is not the pressure the tire is supposed to be normally inflated to. This is the maximum pressure that the tire can safely hold.
On most vehicles, the recommended tire pressure for a vehicle is listed on a sticker in the driver's door jam, or can be found in the vehicle's owner's manual.
Any questions, feel free to ask.