If you’ve ever stood in a tire shop staring at a tire that has a lot of strange letters and numbers on the side that look foreign, you are not the only one. The shop employees always seem to use a lot of terminology that you probably don’t understand.
These strange numbers do have a purpose though: They help you drive more safely, save money on fuel, and help you make wiser financial choices. It may surprise you that having tires not the same size as one another can throw off a lot of things in your car. Things like how your car handles, how fast it can go, how brake response, how fast you go, how much fuel you have, and how accurate the speedometer is. This shows how important choosing the right tires is.
Decoding Tire Size Numbers: Your Complete Tire Specifications Breakdown
Every tire has a size stamped in the side that has a very specific meaning. In order to understand the tire size, you need to understand what it means.
225/60R18 tires follow a standard format where the first number refers to the tire’s width in millimeters, the second number represents the aspect ratio, which is the sidewall height as a percentage of the width, and the letter indicates radial construction. Each number and letter serves a specific purpose, and once you understand what they mean, tire shopping becomes much less intimidating.
Load Index and Speed Rating Demystified
As you hopefully have noticed, on the inside of each tire, after the basic size code, there are two more pieces of information pertaining to your safety.
The first one, the load index, gives you an idea of how many pounds each tire can withstand. If you see an index of 94, that tells you that the tire can hold up to one thousand four hundred seventy-seven pounds.
Then there are the speed ratings, which are marked with an alphabet. If the tire shows an ‘H’ rating, that means the tire can withstand up to one hundred thirty miles per hour. If it is rated ‘W,’ that is an indication that the tire can hold up until one hundred sixty-eight miles per hour. Even if you won’t be driving that fast, it is helpful to have tires with high speed ratings, as that is a good indicator of the tire construction and overall performance.
Please do not try to disregard load and speed ratings to save a little money. It is rather risky to rely on tires that have inferior load and speed ratings, as it puts you at a high risk and could void the insurance you have if an accident occurs.
Service Type Designations (P, LT, ST, T)
The letter that can be found prior to the size numbers tells you what sort of vehicle the tire is made for. “P” is for passenger vehicle tires, which are made for cars, minivans, and smaller SUVs. These tires focus on comfort as well as fuel economy rather than performance.
LT stands for light truck tires, which are built for more load and pressure. These tires are designed for light trucks, larger SUVs, and some commercial vehicles. They are tougher tires, but get lower gas mileage and provide a rougher ride.
The “ST” and “T” designations are for special purposes. “ST” tires are only for trailers and not for any driving vehicles. “T” tires are called “temporary” spares that are only meant for a short distance at a low speed.
Choosing the Right Tire Specifications for Your Needs
In order to choose the right specifications, you need to be frank with yourself on how and where you actually drive. Most people make these common mistakes. They underestimate how much they need to drive, and how important the ride and fuel economy are to everyday driving.
From what you have described, your driving conditions will prove to be the most important factor to consider. Climate, the condition of the roads, and your driving style are the most important when it comes to these driving conditions.
Matching Tire Specs to Driving Conditions
When choosing tire specifications, consider the climate first. If you live where it regularly drops below 45°F, winter tires are a safety necessity while all-season tires lose grip. In contrast, Summer tires are perfect and safe in warm and dry conditions, while being dangerous if the roads are cold or wet.
Urban driving with a lot of stopping and going is different spec tires than highway cruising. In cities, drivers benefit from tires that are comfortable and are nice and quiet. While on the highway, some drivers prefer tires with better fuel efficiency grades.
Performance versus comfort is a priority in its own right. Ultra-high-performance tires are amazing in handling, but provide a harsher ride than touring tires that are designed for comfort. Ultra-high-performance tires also cost more, and wear out quicker.
Plus-Sizing and Tire Specification Changes
When it comes to specifying tires and Plus Sizing, you are able to change the wheel diameter while maintaining the overall diameter of the tire by using lower profile tires. Plus zero is where you keep the same wheel size, which in turn means that plus one is where the wheel diameter increases by one inch, and plus two is where it increases by two inches.
The goal of maintaining overall diameter is to keep the speedometer accurate and to avoid clearance issues. Plus sizing calculators can determine which combinations are compatible, but for major changes, it is better to consult a professional.
Keep in mind that shy profile tires almost always cost more money than standard tires. They wear out more quickly and can offer less protection against road damage. Consider road potholes. The enhanced control and steering might not justify the drawbacks on a busy road.
Electric Vehicle Tire Specification Considerations
Electric vehicles offer more options and challenges when it comes to choosing tires. This is due to the weight, battery, and how torque is instantly delivered. Compared to gas-powered vehicles, load index selection is more important. This is due to the additional weight and how load capacity exceeds expectations.
Maximizing your range is crucial when rolling resistance is low. When trying to get the most out of your battery charge, any lost efficiency is detrimental.
Low noise ratings in tires is especially crucial in EVs due to the absence of a combustion engine. Without the engine noise, any tire noise is going to be more obvious. EV tailored tires and tires with low noise ratings are your best by choice.
Reading Tire Labels: Essential Information Beyond Size
Tires will offer more than just the basic size specifications. European-style labels are becoming more common across the tire industry. In addition to basic criteria, tires will offer rough ratings in measure, wet traction, and noise to track complaints to determine how gas efficiency and tires rack up to each other.
Energy Efficiency Ratings (EU Label System)
The EU grading regulations place tires on an A-G scale, with A being the best grade a tire can receive. Between an A and a G tire, there can be a difference of hundreds of dollars in fuel savings over the life of the tire.
The wet grip rating is important for stopping distances on wet roads and is crucial for the safety of the driver and all the passengers in the vehicle. A tire with a G rating will be problematic in the rain, and wet grip ratings, just like fuel consumption grades, are on the A-G scale.
Tires create external rolling noise, which is measured in decibels. A quieter tire is better for ride comfort, especially on road trips.
TPMS Compatibility and Installation Considerations
TPMS sensors are an important consideration when tire shopping, as not all aftermarket tires will mesh correctly with the vehicle’s TPMS, and some tires will even need different sensors or additional programming to align with the TPMS.
You should consider sensor, stem, and valve types, as well as reset procedures when deciding to install your TPMS. After completing a tire installation, some TPMS systems require a specific reset that your installer should take care of.
TPMS service is an additional cost that can be incurred when purchasing aftermarket tires, so keep that in mind when budgeting for your new tires.
Making Sense of It All
Tire specifications can get really detailed and can be hard to sift through. Remember to focus on what matters for your personal driving needs instead of getting lost in the details.
From simple size codes to more complex performance ratings, the focus should be the same. What are your real world driving needs? What safety concerns do you have? You should remember that there is no single, best tire. Instead, there is the best tire for your needs, your budget, and what you personally value.
Your Questions About Tire Specifications Answered
Is it possible to combine different tire specs on my car?
No, it can lead to dangerous handling issues and can potentially damage the differential or stability systems.
How do tire specs impact fuel economy?
Tires with lower rolling resistance can improve fuel economy. Compared to standard tires, it can lead to a fuel economy improvement of 4-6%.
What tire specs are needed for towing?
You need to get the higher load index ratings and speed ratings that are appropriate for towing. Check the owner’s manual for specifics.
Do tire specs matter for leased cars?
They do. Most lease agreements stipulate you must return the car with the original equipment and violating this can lead to extra lease-end fees.