DIY Network

Tire Alignment and "Reading Your Tires" From "Auto Primer" episode DAPR-101

Besides hosting DIY's Auto Primer, Leilani Munter is also a professional race-car driver.

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In this episode of DIY's Auto Primer, host Leilani Munter covers tire basics, how to handle a flat-tire situation and some valuable information for when it's time to shop for new tires.

In this third segment of episode 101, Leilani talks about some specific things you should be aware of when tire shopping. To do that, she "demystifies" those cryptic numbers found on the sidewalls of tires. They may look complex, but they contain some valuable information. She also defines some terms you may hear when shopping for tires -- specifically, "camber" and "toe."

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Figure A

Tirespeak: Know How to Read Your Tires

When shopping for tires, it's important to know the meaning of all those mysterious embossed letters on the sidewall of the tires. It's not as complicated as you may think. Here's how to decipher them.

• The first letter in the series is the tire's class designation -- for example, "P" for passenger, "LT" for light truck or "T" for temporary.

• That letter is followed by the tread width. In this case, "235" means this tire's tread is 235 millimeters in width. So larger tread-width numbers mean wider tires (figure A).
  

  	Figure B
  	Figure C

• The next number in the series (figure B) is called the aspect ratio -- in this case it's "75." That's calculated in a ratio compares the height of the sidewall and width of the tire. So in this case, "75" means that this tire's height is 75-percent of the total 235-mm width.

• The aspect ratio is followed by a letter that tells what type of construction this tire has. In this case, "R" stands for radial. (Most modern tires are radials. In radial tires, the internal tread-wires run perpendicular to the direction of the treads.)

• The letter indicating construction is followed by a number (figure C) designating the diameter of the wheel. In this case, this particular tire is made to fit a15-inch wheel.
  

  Figure D
  Figure E

• The last number in the series (figure D) is the load index which tells the amount of weight the tire can hold. Higher load-index numbers indicate greater load-carrying capacities. In this case, "105" indicates that this tire can hold up to about 2000 pounds.

• The last letter in the series is the speed rating. Tires like this with an "S" rating (figure E) can handle speeds up to 112 mph. Letters later in the alphabet correspond to higher speeds. A "Z" rated tire, such as some high-performance tires, can handle speeds up to around 190 mph.
  

  	Figure F
  	Figure G

• The treadwear rating number (figure F) indicates how long the tread will last under typical driving conditions. The higher the number, the longer the tread will last. On this high-performance tire, the "220" indicates that this tread has a relatively short live, compared to some other tires. (Because of the materials and configurations, high-performance tires typically wear faster than more standard tires.)

• The traction rating is an indicator of the level of traction the tire possesses. Traction ratings can range from A to D. In this case, this high-performance tire gets a "AA," indicating a high level of traction.

• The temperature rating is also an A to D letter rating (figure G), with A being the highest rating. In this case, the "A" means that this tire can withstand temperatures even in very hot climates such as Arizona.
  

  Figure H

Proper tire alignment is critical to the tread-life of your tires as well as to your car's steering performance. Improper alignment typically produces uneven tread-wear (figure H) either to the inside or outside shoulder of your tire. Simple alignments, at the proper intervals, will save you money in the long run in tire costs. It's best to have your car aligned at least once a year.

Alignment Spec: Camber

If your tires are wearing faster on one side or the other, your camber probably needs adjustment. Camber is the angle of the wheel against level ground when viewed from the front of the vehicle. If the top of the wheel leans out (figure I), then you have positive camber.

If the bottom leans out (figure J), then you have negative camber.

For most vehicles, at highway speeds, slightly negative camber works best.

Figure I

Figure J

Figure K

Alignment Spec: Toe-Setting

If your car's tires have a "saw-tooth" wear pattern (figure K), it's likely due to an incorrect toe setting. This measurement indicates whether your tires are parallel when the car is pointed straight ahead.

Toe-in means that the fronts of the tires are closer together and pointing towards each other (figure L), while toe-out means the opposite -- that the fronts are pointing slightly away from each other (figure M).

Figure L

Figure M

Zero-toe -- or perfectly parallel tires -- is typically best for street-driving.

Leilani's Racing Factoid: Race cars, like this one driven by Leilani , may have the camber and toe of their tires adjusted in various ways to adapt to different race-track conditions, degrees of banking, etc.

In the segment that follows, Leilani shows some tire-related products.

RESOURCES :

The Complete Idiot's Guide to Trouble-Free Car Care
Author: Dan Ramsey
ISBN: 0028635833
Alpha Books

Tires, Suspension and Handling
ISBN: 1560918314
Author: John C. Dixon
(Society of Automotive Engineers

Auto Repair for Dummies
Author: Deanna Sclar
ISBN: 0764550896