How to Read Tire Size

Have you ever looked at your tire and think what do these numbers actually mean? It almost looks like a secret message under a code that’s hard for us to decode. But fear not; far from all these mythical thoughts these numbers engraved on the side walls of your tires are in fact the summary of what exactly you need to know about the tires you own.

These numbers are significant and play a vital role when it comes to exchanging tires. Each individual number stands for the particular criteria it represents. If you could only know what they truly abbreviate it’s a cake walk for you to know your tires better.

How to Understand Tire Sizes

Let’s take a usual structure titled “P220/50/R1698H”.

Here P identifies the tire as one of the Passenger Tires. In simpler words P stands for PMetric. If your tire starts with LP instead of a P, then it means your tire is a Light Truck tire.

The number 220 represents the width of the tire which refers to the measurement from the sidewall to sidewall in millimeters. These measurements are not constant and often vary depending on the rim to which the tire has been fitted. Also you can check our other article called How to Remove Tire From Rim?

50 the two-letter figure signifies the aspect ratio. This is actually the percentage comparison between the tire section height and width. For instance, the aspect ratio of 50 as in this case, means that the tire section height is 50% of the tire section width.

R modifies the construction sort used within the tires casing. R stands for radial construction. B means belted bias and similarly D represents diagonal bias construction.

16 showcases the last dimension listed in the size is the diameter of the wheel rim. In most of the cases which is recorded in inches. In case of replacing or exchanging the tires this the section you should keep your eyes on. Last but not the least!

The last two-letter figure at the very last are the numbers to decipher load support and index rating.  The load index tells you how much weight the tires are capable of carrying. Load indices usually hold a range from 75-105 for passenger tires where each of the numeric numbers is the counterpart that corresponds to a certain weight capacity.

At the last the letter “H” is one of the speed ratings that is meant to range among A-Z. Each of these letters are meant to compliment the maximum speed a tire is able to sustain under its recommended load capacity. On each U.S. passenger tire the load limitations are marked in pounds. However, European tires have both the list in pounds and kilograms.

Here is a list of the letters equivalent to its optimized speed. Even though tires can perform equivalent to its maximum speed limits. Continental Tire does neither favor in exceeding legal speed boundaries nor advocating them.

How Long Can You Drive on a Spare Tire?

One has to check their owner’s manual to find the answer to this question. But it is safe to say that 100 kilometers is the rule of thumb. These tires are not intended to provide long-range service. You should not drive over 50 mph and no more than 50 miles with a donut-sort spare tire. Driving for a long time in spare tires can result in permanent damage to the other car parts with the transmission included.

No matter how conscious you are on-road, trouble always has a clingy way of lingering over your head. Realizing you have a punctured tire is one of the most frustrating things a driver can experience while driving. Even in the worst case scenario a spare tire still has enough life that will enable you to reach your nearest repair shop or your garage. Yet the question remains.

How long can you ACTUALLY drive on a spare tire?

Contradictory with the previous answer mentioned above a very recent answer from an ASE-certified technician stated “it depends”. And since then this answer is getting more and more approved than the other.

Every car in older days came with a spare tire that matched the tires already on the vehicle. Over the emerging years, car manufacturers have realized the spare tire is used very infrequently. It didn’t make much sense to buy every ride that comes with an adhesive full-size spare tire. Thus, manufacturers began securing a space-saver also known as “Donut” in exchange for full-size spare ones.

They also re-created a new type known as “Run-flat” tires. With all these updated features, the type of spare in your vehicle will determine the distance and how long one can drive before purchasing a new one. Also get the comparison of our article 285 75r17 vs 285 70r17 Tire before purchase.

Full-size spare tire

In case you have discovered that your original tire cannot be repaired, you can fit this tire on the original’s rim only after you have checked the spare tire’s air pressure.  This process is cheap, easy and quick and will definitely buy you some extra miles with a longer period of driving time.

Safe-Saver/Donut Spare Tire

A general rule is applicable with these tires is not to exceed the speed limit of 50 miles per hour. And drive no more than 70 miles before replacing your donut with a new tire. But keep in mind that these tires are only for short time usage as they are vulnerable to road hazards and are also much smaller than the rest of the alternative types.

A Run-Flat Tire.

These tires are becoming more popular as they cost less compared with the traditional tires. In the case of BMW or a MINI you are good to go with these tires by your side. These tires are tougher than the most of the spares and are hard to penetrate through yet not built to last forever. You can drive up to 50 miles before the need of it being replaced.

Closure

Regardless of the type of the wheels, your spare tires are not going to last forever. It demands to be replaced or repaired sooner rather than later.

Frequently Asked Questions (FAQ)

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