Tips to Read Tire Sizes

Many people don’t know the meaning of the numbers and letters mentioned on the sidewalls of their vehicle’s tires. In fact, most don’t even know that they exist! However, these are quite important, as they provide useful information regarding, among other things, the size, air pressure requirement, load capacity, and construction type of each individual tire.

Information about the tire size can be found on the sidewall of a tire, typically inscribed between its name, and the name of its manufacturer. It is an alphanumeric series, which differs from tire to tire based on its class and other specifications, such as the type of construction, aspect ratio, etc. In the following lines, we will explain the meaning of each element in this series in order to help you read and comprehend the information pertaining to the size of the tire on your vehicle.

Tire Size: Explanation

  • The series normally begins with the class of the tire, usually the letter ‘P’, which denotes that it is a ‘Passenger Car Tire’. It can also be ‘LT’, which indicates ‘Light Truck’, ‘T’ for ‘Temporary Spare’, or ‘ST’ for ‘Special Trailer Service’.
  • The three digit number followed by the letter ‘P’ denotes the width of the tire in millimeters.
  • The next number following the width represents the ‘Aspect Ratio’ of the tire, which is the ratio of the height of the tire to its width. For a regular tire, this ratio lies between 50 to 70.
  • After this number, you will find a letter which gives the type of construction of the tire. This letter is usually ‘R’, which stands for ‘Radial Construction’. It can also be ‘D’, which stands for ‘Bias Ply Tires’ or ‘Diagonal Tires’, or ‘B’, which indicates ‘Belted Bias Tires’.
  • The number which comes after ‘R’ denotes the ‘Diameter of the Wheel’ in inches. Usually, the diameter of the wheel ranges from 13 to 22.

After a gap, there is another number followed by a letter, which are together called the service description. It is a combination of load index and speed symbol.

  • The number in this combination stands for ‘load index’. It indicates the maximum weight a tire can carry under certain service conditions, and ranges from 71 (761 lb) to 110 (2,337 lb).
  • The letter which follows this number is the ‘speed symbol’ or ‘speed rating’. It is the maximum rated speed for the tire at the specified load.

The recommended air pressure is written on the tire rim.

Tire Size Example

If the number on the tire is ‘P205/75R15 89H’, then the meaning of its tire size can be decoded as following:

A passenger car tire of width 205 millimeters, having an aspect ratio of 75, and radial construction which has 15 inches of wheel diameter, and can carry 1,279 pounds of load at the maximum speed of 130 MPH (210 KPH), under certain service conditions.

Knowing how to read the tire number is especially important when you change the tire. It is not safe to use a tire which does not meet your vehicle’s tire specifications. Using a tire of inappropriate size can also affect the speedometer accuracy, power, and traction control of your vehicle. Now that you know how to read tire sizes, it will not only come in handy when you are changing the tires, but also prove useful in selecting an appropriate one.

Risk of Driving with Bald Tires

A recent survey done by the Rubber Manufacturers Association found that over 85 percent of American drivers do not know the proper procedure to inflate tires, and to what pressure. Also, approximately 30 million American vehicles have at least one bald tire. It is inevitable that car tires wear down over time. However, driving with bald tires and having a tire failure can be disastrous, leaving you without any control on the vehicle, or stranded in some godforsaken place without any way to get home. Driving with bald tires is like gambling; the tires are sure to give way sooner or later. It is important to perform regular checks and replacements to have a safe ride. Besides, driving with good tires makes the entire experience more relaxing and easy. It is recommended that the tire tread be checked at least once a month.

Diving at high speeds, improper inflation, hard cornering, and improper alignment result in quicker wear and tear of the tires. So, why are bald tires dangerous? Let’s find out.

Dangers of Driving with Bald Tires

  • Bald tires do not have enough tread, which can result in a blowout or other forms of damage to the vehicle, especially when going over potholes at high speeds without any warning.
  • Bald tires are old tires, and old tires tend to get damaged more easily with hard impacts, which makes controlling the vehicle difficult in emergency situations.
  • Due to the low amount of tread, handling in a vehicle becomes more difficult than usual.
  • Using bald tires in snow or icy conditions is risky, as less traction will cause the vehicle to slip and skid due to strong winds or large vehicles that pass by.
  • It is nearly impossible to brake safely during emergencies, and this usually ends with disastrous results.
  • Similar to driving in winter conditions, using bald tires on wet roads in the rain is risky, and can lead to the vehicle slipping and skidding. It can even cause the vehicle to hydroplane, making it near impossible to control.
  • Bald tires in extremely poor condition might cause shaking of the steering, which is a imminent sign to get the tires replaced.
  • Driving in such a condition requires more alertness and attention, and as a result, causes fatigue even faster, which can cause accidents, especially when driving for long distances.

Other Disadvantages

  • Due to lack of traction, bald tires can affect the rate of acceleration and the overall performance of the vehicle.
  • Such tires also tend to get punctured more easily.
  • Bald tires do affect gas mileage, because they have lesser traction, which makes the engine run harder, giving poor fuel economy.
  • Driving with bald tires is illegal. You can get a ticket for this if a police officer stops you for any reason.
    If you are involved in an accident, bald tires can be used as a proof of negligence against you, and you may have your insurance amount increased, and could also get sued by the other party involved in the accident.

How to Check for Bald Tires
Ideally, the tread of a tire should not be less than of 1/16 of an inch. In wet or snowy conditions, it is best to have more than double of that. One can find out the depth of a tread using a gauge. However, there is an easy test to check the approximate depth of the tread, and it will only cost you a penny.

Lincoln Penny Test : For this method, you will only need a penny that is stamped with the Abraham Lincoln’s face. All you have to do is to insert the penny upside-down with the top of Lincoln’s head going into the tread. If the top of the head is covered by the tread, the tire is still usable and has a safe amount of tread left. However, if the head is visible at any point of the tire, it is time to replace this bald tire with a new one. It is important that while you check if your tire is bald, look for cuts, cracks, punctures, bulges, and splits, as these can dramatically shorten the lifespan of the tire. Ideally, one should replace all four tires at the same time. However, if you are on a budget, then replace two tires together, and place the new tires on the rear, as this will give better control.

Tread Wear Indicator Bars: Newer tires have tread-wear indicators that are built into the tires. If a tire is worn out, flat rubber bars appear on the tire perpendicular to the direction of the tread. If you notice more than one of such bars on your tire, it is time to go shopping for replacements. Bald tires also tend to make a humming/squealing noise while rotating, giving you an indication to get them changed.

Precautions: It is recommended that you measure the tire pressure at least once a month, maintaining it at a pressure of the manufacturer’s recommendation; rotate the tires after every 5,000 miles, with a thorough visual examination; and check for over-inflation, under-inflation, worn areas, unbalanced tires; and rectify any problem to prolong the tire’s life.

Driving Safely with Bald Tires
If you are really strapped for cash, and are unable to afford new tires, there are a few tips to follow which will make driving with bald tires much safer.

  • Driving slower will give you better traction and control over your vehicle. So make sure that you give yourself some extra time when going somewhere.
  • When driving up or down an incline, especially in icy conditions, it is important to drive on lower gears, and to maintain a steady speed.
  • Keep a good amount of distance between yourself and the vehicles in front of you. This will give you enough time to control your vehicle in case of emergencies.
  • If you are diving in poor weather conditions, always be very alert, as a vehicle with poor traction can easily get into an accident.
  • If you are driving in snowy conditions with bare tires, try and drive behind salt trucks, and keep your temptation to brake hard under control. Vehicles with poor traction spin out of control due to heavy braking.
  • Instead, take your foot off the gas and allow the vehicle to decelerate a little, before slowly but firmly pushing the brake down.
  • Also, choosing a vehicle with manual transmission will give you better control, so you can keep this in mind if you are planning to buy a car.
  • Avoid using cruise control as far as possible.
  • Regularly check the tire pressure.

So, regardless of how many safety-related features your vehicle has, the tires are the only parts that are in contact with the road. Therefore, tires are effectively the most important part of the vehicle for your safety. Keep the tires well-maintained at all times and stay safe.

Ideas to Effective Storing of Tires

With the advent of different tires for use in different weather conditions, it is pretty common for people to have a set or two of spare tires. This brings up the issue of proper storage, which plays a vital role in preventing damage caused by exposure to sunlight and oxidation. Improper storage can lead to changes in the physical properties of the tires, and affect their appearance and performance for the worse.

One of the key problems to be taken care of during storage is outgassing, i.e., evaporation of lubricating oil from the outer surface of the tires, which causes cracks to develop. So, do you think you’re storing your tires in the right way? Just go through the article to find out.

Useful Tire Storage Tips
Here are a few things that you should take note of, in order to maintain the performance of your tires even after they have been stored for a season or longer.

Protect your tires from exposure to ozone, as the gas can damage rubber. For this, you need to ensure that there are no ozone emitters, such as basement sump pumps, located close to where you store your tires.
Tire totes are another great way to store tires. They are not only effective in providing protection from the elements, but are also easy to carry. However, they are not airtight, but you can counter this problem by securing the tires inside airtight plastic bags before you place them inside the tire totes.
Special care should be exercised while storing whitewall tires and tires with red lines. While stacking these tires or placing them in a row, place them in such a way that no black surface faces a white surface or one that has a red line on it. Wondering why? It’s because the black rubber that borders the white surface or red line has a different composition than that of the black rubber on the other side. This prevents the whitewall from getting stained with oils from the black rubber surrounding it. However, if the white surface comes in contact with the black rubber on the opposite side, it may develop a stubborn stain that is difficult to remove.

Whitewall Tire

Red Line Tire
Humidity is another factor that you should take into consideration while deciding where and how to store your tires. Atmospheric moisture can damage the rubber used in tires, which makes it essential to store them in a dry place, instead of dumping them in the garage or the shed in your backyard. However, in case you have no option but to store them in a place that is not dry enough, make sure you wrap them securely in airtight plastic bags.
Place the tires in a clean and airtight plastic bag. This protects the tires from being exposed to atmospheric moisture. You can even take a step further and use a vacuum cleaner to suck out air from within the bag, and then seal the mouth of the bag with tape. This will create an airtight environment for the tires and increase their life, by keeping outgassing to a minimum.

When you’ve a car that you do not intend to use for an extended period of time, it is recommended that you remove the tires and store them separately. Otherwise, the weight of the car can damage a specific area of the tire’s surface, which in turn, can lead to premature aging of the rubber. Once the tires have been removed from the vehicle, you can place them on a jack stand till the time you’re required to use them again.
Always store the tires away from direct sunlight, because prolonged exposure to heat and the ultraviolet rays of the Sun can damage the rubber.

Never store tires that have dirt and grime on their surface. Always make sure you clean your tires thoroughly with soap and water, using a tire brush to gently remove the dirt from the areas between the tread patterns. However, abstain the use of acid-based cleaners as they do more harm than good. If you’re storing tires that are mounted on rims, use a wheel brush to remove dirt from the rim surface and wash it with soap and water. Also, ensure that they are completely dry before you store them, because accumulated moisture can adversely affect the rubber, and damage your tires.

Storing Rimmed and Rimless Tires
While the tips given above are the same for all tires, tires mounted on rims have a different set of storage requirements than rimless tires.

Tire Mounted on Rim

Rimless Tires

  • Should not be stacked one above the other
  • Should not be hung during storage
  • Should be placed next to each other in an upright position

Tires with Rims

  • Should not be stored in an upright position
  • Can be hung during storage
  • Can be stacked one above the other

So, you can see that storing your tires is not as difficult as you might think. Just follow the simple steps given above, and you’ll no longer have to worry about the performance of your tires after you have placed them in storage for a season or even longer.