Porter's Tire Store Info Center

Take a few minutes to read these helpful guidelines and take a look at the links, which will help you understand key information.

Determine When You Need Tires
  • Tires are considered to be worn out at 2/32 inch minimum tread depth.
  • In wet conditions 4/32 inch or less tread means a significant loss of wet traction due to shallower grooves and sipes.
  • In snow conditions, traction noticeably diminishes at 6/32 inch tread depth. Shallower lug and groove depths limit a tire's ability to "bite" into snow and clean out snow compressed into the tread.
  • Irregular wear necessitates early tire replacement.
Determine How Many Tires You Need
  • If you need one tire (due to damage, a defect, irregular wear, etc.) it is recommended that you replace it with a tire that has a similar brand, line, speed rating, and load capacity to your three remaining tires.
  • If you need two tires due to poor or irregular wear, replace the tire with ones of similar or better quality.
  • Replacing all four tires is the best case scenario, as you are open to a wide range of options.
Determine the Tire Size

Most people replace their old tires with the same size that was on the vehicle. If this is your choice, there are various locations you can check to determine tire size.  You can also find this information in the owner's manual for your vehicle. Finally, you can check your vehicle's tire placard. The placard is often located inside the glove box door, fuel door, doorpost, or door edge of your vehicle.

Changing tire size can often improve the ride and performance of a vehicle through the following methods:

  • By selecting a tire of the next lower profile, you can significantly improve the ride quality and handling of your vehicle. On small cars, a good example is to replace the original equipment. The tread is almost an inch wider and the tire has a proportionately lower sidewall (however the tire's height remains the same). Both of these features improve handling and stability.
  • Plus sizing has become very popular. In this application, the plus size tire is the same height as the original but its sidewalls are shorter. This change delivers improvement in tire response and handling.
  • Upsizing, or selecting a larger tire, is a common option, especially for SUV and truck owners. Taller, wider tires improve performance as well as ride quality On trucks, larger tires can improve traction, load carrying capacity and appearance. Because cars and trucks are equipped with computerized systems (ABS for example) that use feedback from tire rotation, use these guidelines to select a larger tire:
    1. Make sure the tire has load carrying capacity equal to or greater than what the vehicle placard suggests
    2. Verify that the rim width range is appropriate for the tire to be installed.
    3. Confirm that the tire-to-vehicle clearance, lock-to-lock steering and suspension clearance is such that no rubbing occurs.
Analyze Your Driving Conditions

A person who lives in southern California will often choose a significantly different tire for their car than someone who lives in Minnesota. There are exceptions to the rule, however. The person who lives in California may go on a skiing or off-roading trip. The person in Minnesota may only drive on plowed roads during snow season. Therefore, their driving situations may include a variety of conditions.

Here are some guidelines to help you select the right tire based on your driving conditions:

  • Analyze your average driving conditions to determine if you most frequently drive on dry roads, a combination of both wet and dry roads, or primarily wet roads. Then, factor in the possibility of seasonal extremes. Most tires purchased today are the all-season type that appeal to the great majority of drivers who seek acceptable performance and traction across the spectrum of possible driving conditions in all four seasons. Look for the M&S symbol on the sidewall to ensure the tire's mud and snow rating for winter use.
  • Consider seasonal tires. All-season tires have performance and traction disadvantages since their design elements are averaged. In the fast-growing performance market segment, two newer strategies have become popular. In non-snow climates, summer or dry type designs are emerging as year-round favorites. These designs feature far superior dry handling and traction with wet performance ranging from acceptable to excellent. Performance enthusiasts who live in more extreme winter climates also use these new designs when seasons allow and change over to winter tires once the snow begins to fall.
  • If you drive a pickup truck or SUV, chances are you'll be considering a purpose-built tire design to match your driving needs. These designs have tradeoffs including traction (both on and off the road for various conditions), highway ride quality, and performance. In terms of traction, designs range from HT (highway tread) to AP (all-purpose) to AT (all-terrain) to MT (mud terrain) in order of aggressive tread design. Highway ride quality diminishes as the tread design becomes more aggressive.

You can pick tread aggressiveness according to your needs, but be mindful of the highway ride quality tradeoff. Most SUV owners select AP type tires for their balanced highway ride and all-season traction. Sport truck tires with all-season tread designs are quickly gaining popularity among SUV owners, however. These drivers are looking for better handling when on the highway and are willing to settle for less traction off-road. Meanwhile, pickup truck owners continue to sustain their "purpose-oriented" tire selection, with AT tires remaining the most popular type in this market segment. However, Sport truck tires are showing gains among those who like great highway handling and need a tire that can handle truck load capacities.

Buy the Best Quality You Can Afford

The old adage, "you get what you pay for", may have been invented for tire buying. A good exercise would be to calculate the total price for your tire purchase and divide that by the miles of service to get the cost per mile. You'll quickly see that the better tires are the better value. When you have mileage guarantees to compare, this calculation is very easy, but there is another way. When you are comparing tires within a particular brand, use the UTQG (Uniform Tire Quality Grading) ratings (treadwear grade) to calculate value. Divide the tread wear rating by the price. The highest number should be your pick if you want the best value according to treadwear grade. This system won't help you compare between brands, however, because there is no standardization for wear scoring. Traction and temperature ratings are standardized, however, and are useful for making comparisons between brands.

Consider Performance and Speed Ratings

Most people are aware of speed ratings. Simply put, you need to buy a tire with the appropriate speed rating for your vehicle. In Europe, the law mandates that the original equipment tire must be replaced with a tire possessing the same or higher speed rating. However, in the US you can buy a lower (and less expensive) speed rated tire of the same size. If you do this, be aware that you are limiting your vehicle's performance in terms of handling and speed capacity. Generally speaking, a tire's handling response corresponds with its speed rating. Look at it this way: you'll lose that crisp handling the manufacturer designed into the vehicle and you will not be able to safely achieve the speeds the vehicle was designed for if you use a lower speed rated tire than the original design. Conversely, you can improve your vehicle's handling with a higher speed rated tire.

Consider Performance and Speed Ratings

Each year more car, light truck, and SUV designs are introduced. As a result, tire manufacturers are responding with more specialized designs. Be aware that for a given vehicle you can choose anything from long-wearing, easy-riding tires to style-conscious, ultra-high performance tires. It's your call. We have many different types of tires to fit a wide range of vehicle styles and driving habits.


 A wide range of tire choices is available for every vehicle. Understanding the types of tires will help you make the right choice. Tire types can be grouped by their application: Cars and Minivans, Trucks and SUV, and Winter Tires.

Tire Types for Cars and Minivans

 Passenger tires

Passenger tires are among the most cost-effective tire types available. Mohave and Rocky Mountain brands typify excellent value at the entry-level. Premium tires such as the Arizonian Silver Edition offer longer wear and even lower cost-per-mile operation. Passenger tires commonly include the following features and options:

  • Higher profiles (80, 75, 70, or 65 series) for smoother ride and longer wear
  • Lower speed ratings (Q, S, and T) with a harder, longer wearing compound
  • All-season tread designs for year round wet, dry and snow traction
  • Tread patterns that emphasize high ride comfort and low noise
  • White or black sidewall finish
  • Tread wear guarantees ranging from 30,000 to 85,000 miles or more

 Touring tires

Touring tires feature enhanced performance blended with excellent ride quality. Designs range from high mileage S and T-rated tires such as the BFG Precept, Pirelli P3000 and Goodyear Assurance to performance oriented V-rated designs like Pirelli's P6 Four Season. Touring tires commonly include the following features and options:

  • Slightly lower profile (from 70 to 55 series) and wider tread than an equivalent passenger tire for improved handling and stability "at speed"
  • The widest range of speed ratings (S, T, U, H and V), of any tire
  • Numerous wear, handling, and ride quality tradeoffs (The touring tires a minivan owner selects can be very different from the touring tires a BMW owner selects.)
  • Predominantly all-season tread designs (Although a number of dry or summer designs are available.)
  • Tread patterns that emphasize performance blended with ride comfort and low noise
  • Contemporary black sidewall styling (Few touring designs offer a white sidewall finish.)
  • Optional tread wear guarantees, which diminish as speed ratings increase

 Performance tires

Performance tires are specialty tires that customers choose to enhance the look and low speed traction of their vehicles. The Goodyear Eagle GT II is a good example of this tire type. Performance tires commonly include the following features and options:

  • A very wide range of profiles and tread widths to select a special look (Muscle cars, vans and street trucks commonly use this tire type.)
  • Lower speed ratings (S and T) that help keep these tires very affordable
  • All-season tread designs with year round wet, dry and snow traction
  • Tread patterns that emphasize low speed traction and handling
  • Raised white lettering or black lettering (on either sidewall) to provide styling choices
  • Tread wear guarantees ranging from 40,000 to 50,000 miles

 High Performance tires

High Performance tire design extends high speed handling and stability. Cooper's Zeon ZPT typifies excellent value in an H-rated high performance tire design. High performance tires commonly include the following features and options:

  • Lower profiles (as low as 40 series) and larger diameter wheel sizes (up to 17 inches) which stiffen sidewalls for improved cornering response, lower rolling resistance and increased tread stability
  • H (130 mph) and V (149 mph) speed ratings, which offer control "at speed" for high performance cars
  • All-season designs (Although dry designs deliver superior cornering response and high-speed stability in wet and dry conditions.)
  • Tread designs with an emphasis on maximum contact patch
  • Softer tread compounds for better traction
  • Lower UTQG ratings and shorter treadlife
  • Sophisticated belt and cap ply packages that help maintain a maximum contact patch and optimum tire shape at high speeds
  • Numerous bead and sidewall enhancements that stiffen the casing for better cornering response and high speed stability

 Ultra High Performance tires

Ultra High Performance tires take material and tire design technology to the limit. These are the tires for today's most sophisticated sports cars and sedans. All-season designs such as Michelin®'s Pilot Sport AS deliver year round traction. The Pirelli P-Zero Nero typifies a tire designed for extreme performance with the largest contact patch in its class. Ultra high performance tires commonly include the following features and options:

  • The lowest profiles attainable by design and material technology, as low as 25 series, that deliver the greatest control and response at speed (Tire diameters up to 22 inches and cross-section widths up to 345 mm are available.)
  • W (168 mph), Y (186 mph) or Z (over 149 mph) speed ratings, for the ultimate in high-speed control
  • Asymmetric and directional tread designs that maximize dry contact patch and wet control (All-season designs compromise extreme performance for year round usability.)
  • "Sticky" tread compounds that trade off treadlife for performance (The UTQG tread wear ratings for ultra high performance tires are the lowest of any tire designed for everyday street use.)
  • Design innovations and exotic lightweight materials to enhance handling and high-speed control
  • Designs that deliver a smoother, quieter ride (A vehicle with an ultra high performance suspension is required to receive the full benefit.)

 Competition tires

Competition tires are built for racing classifications that require a DOT-approved tire. Yokohama's A032R is a popular choice among autocross racers. Among front-wheel drive enthusiasts, the BFGoodrich® g-Force Drag Radial is often the choice for faster quarter mile times. While legal for the street, the racing compounds and virtually groove-free designs make these tires impractical for most users. Competition tires commonly include the following features and options:

  • R compounding specially designed for racing (Heat cycling competition tires will improve wear and traction.)
  • UTQG tread wear ratings below 100
  • Minimum tread depths that deliver improved racing traction
  • A racing belt package that stiffens tread to maintain maximum contact patch under extreme steering response
  • Massive block designs that approach racing slick traction
  • Drag slick designs that feature flexible sidewalls which maximize traction during acceleration

 Tire Types for Trucks and SUVs

AP tires

AP type tires are original equipment on many of today's vehicles due to their smooth, quiet highway ride and good all-season traction. Often referred to as All-Purpose or Mud and Snow designs, the Pirelli Scorpion STR and Michelin® LTX M/S are good examples of this tire type. AP type tires commonly include the following features and options:

  • All-season tread designs and full-depth siping that provide confident traction year round
  • Quiet, stable highway ride
  • A wide range of sizes (from 14- to 17-inches), and load carrying capacities
  • Compounds that emphasize good wear and traction in a wide range of temperatures
  • 40,000 miles of service

Sport Truck tires

Sport Truck tires bring sports car handling to the truck and SUV marketplace, yet they are built to handle the suspensions and load carrying capacities of trucks. Cooper's Zeon XST and Pirelli's Scorpion Zero are excellent examples of this tire type. Sport Truck tires commonly include the following features and options:

  • All-season tread designs that emphasize street handling and traction year round
  • Wheel sizes up to 26-inch diameter and section widths up to 325 mm with profiles as low as 25 series
  • Standard and reinforced load capacities combined with large sizes to provide sufficient load carrying for trucks and SUVs
  • Speed ratings up to Z (149+ mph)

 All Terrain tires

All Terrain tires are a step up in off-road traction from the AP designs. This is arguably the most popular truck tire category. Most users are willing to accept the highway ride tradeoff in order to get the additional traction. Our Pathfinder AT and the BFGoodrich® All Terrain KO are both extremely popular tires in this category. All Terrain tires commonly include the following features and options:

  • Tread design with larger blocks and greater void (area where there is no tread) for better clean out of mud and snow
  • A wide selection of sizes for pick-ups and SUVs of all types and load-carrying capacities
  • Ply ratings that range from four-ply to eight-ply for many sizes, with extreme ten-ply or twelve-ply ratings available in special sizes
  • Mud and Snow rating
  • Designs that wear longer and ride more quietly over the road

 Mud Terrain tires

Mud Terrain designs represent the extreme in traction tires that are still acceptable for highway use. The emphasis is on off-road traction for those whose hobby or business requires the ultimate grip in mud, sand, rocks, or any possible off-road condition. The Goodyear Wrangler MTR and BFGoodrich® Mud Terrain KM are excellent examples of tires in this category. Mud Terrain tires commonly include the following features and options:

  • Tread designs that feature the largest possible block sizes and high void ratios for grip and durability under harsh off-road conditions
  • Sizes that range up to the very tallest and widest available for increased flotation and axle clearance
  • Ply ratings that range up to eight-ply (Extra sidewall and tread reinforcement plies are often added to protect against puncture.)
  • Tread compounds with silica added to stiffen the blocks for improved durability and wear
  • Refinements in noise reduction and highway control to make the tires more "streetable"

Winter Tires

Winter tires are more specialized than many people think. People often associate winter tires with old forms of snow tires that were loud, mounted on the rear of the vehicle and needed studs for traction when driving in icy conditions. Today's technology has changed all that. Winter tires for cars and minivans are now applicable to a wide range of drivers and vehicle types. These tires are ideal for drivers who may encounter a wide range of potential winter conditions including snow, ice, slush, rain, and freezing rain. However, these tires remain applicable for dry highway conditions as well. A lack of winter tires poses a threat to safe driving when serious weather conditions suddenly arise. Because of the significant traction improvement of winter tires, especially in colder temperatures, they should only be used in sets of four. Winter tires commonly include the following features and options:

  • Tread designs that balance a smooth, quiet ride (not much different than your "other" tires) with instant traction when bad winter weather develops
  • Advanced design in tread compounds, including soft, microfilament grip materials that stay pliable in the coldest temperatures
  • Superior snow and ice traction without the need for studs (Some designs allow for studding, however, for those who live in more extreme climates.)
  • Additional siping (very small slits in the blocks that give extra gripping edges across the treadface), which enhances traction for any road condition but is especially useful for snow and ice
  • Q-, S- or T- speed rating for the everyday driver


Winter tires designed for performance vehicles are intended for the driver who needs enhanced winter traction but wants as much responsive, high-speed handling as possible. Performance winter tires commonly include the following features and options:

  • H speed rating (Although a few V-rated models are available.)
  • Directional and asymmetrical tread design which increase performance traction (These must not be intermixed. Use the same product for all four tires.)
  • Special tread compounds that remain pliable in extremely cold weather and incorporate microfilaments for extended snow grip
  • Additional siping (very small slits in the blocks that give extra gripping edges across the treadface), which enhances traction for any road condition but is especially useful for snow and ice
  • Sizes up to 18 in wheel diameters, cross section widths up to 285 mm, and profiles as low as 40 series