The first measurement on a tire size sequence is the tire classification. General consumer-grade tires have 4 classifications based on their general usage roles. These classifications are listed as one or two letter symbols at the beginning of the full tire size molded into the sidewall of all tires.
The 4 general tire classifications are:
- P = Passenger Tire
- LT = Light Truck Tire
- ST = Special Trailer Tire
- T = Temporary Tire
What Are Passenger (P) Tires
Passenger tires, also referred to as P-Metric, are designed for use personal use on common passenger cars, trucks, and SUVs that don’t tow or carry heavy loads and are under 3/4 ton. For instance, you shouldn’t use passenger tires on a 3/4 or 1 ton work trucks and delivery vans.
You can tell if a tire is a passenger tire by looking for the “P” at the beginning of the tire size specification.
There are tires with no classification prefixing the tire size. These are referred to as Euro-Metric tires. They are essentially identical to to P-Metric tires but there are situations where the load index may differ.
Passenger tires have more sidewall flex when compared to LT tires, which helps improve performance and ride quality. Generally speaking, they are a much more comfortable tire for regular commuting.
Can You Put SUV Tires On A Car?
Smaller to midsize SUVs use the same tires that are used on cars. Very large SUVs often need to use LT-metric tires that have stronger sidewalls due to the increased vehicle weight or need to carry heavy loads.
An LT tire will make for a very uncomfortable ride on a car and won’t perform nearly as well as when used on the appropriate type of vehicle. Light Truck (LT) tires shouldn’t be put on a car, but SUV tires that are P-metric are fine for use on cars.
Can You Put Passenger Tires On A Light Truck?
Passenger tires shouldn’t be used on light trucks due to the sidewall construction not being designed to properly handle the more extreme stresses of very heavy light trucks. Light trucks often haul heavy loads or tow significantly heavy trailers and contents. Passenger tires are not capable of supporting this excess weight properly.
Light truck tires are specifically designed for this job and should always be used on light trucks that require this type of tire to safely operate without worry of overheating the tire plies and having the tire fail under load.
What Are Light Truck (LT) Tires
Light truck tires, also referred to as LT metric, are intended for use on 3/4 ton and 1 ton pickup trucks and work vans. They are designed for carrying heavier loads that are often required with work trucks and vans.
Light truck tires have a harsher ride due to the stiffer sidewall construction required to increase the load index to allow them to support more weight.
LT tires are also capable of handling some off road terrain due to the increased structural reinforcement of the sidewalls required for the rougher surface.
Light Truck Vs Passenger Tires
The mail difference between LT-metric and P-metric tires is the stronger sidewall construction used in LT-metric tires which increase load carrying abilities, reduce ride comfort with less ability to absorb bumps, and they will make more road noise.
Most all-terrain and mud tires meet the light truck tire metric instead of the milder passenger tire metric due to the more rugged construction and design.
Light Truck Tires Vs Trailer Tires
Light truck (LT) tires are radial tires that have been constructed to handle heavier loads. Special Trailer (ST) tires are also designed to handle heavy loads but are usually a bias ply construction instead of radial ply.
Bias ply will have stiffer sidewalls and increased load carrying capabilities. They will also not have as much sidewall flex so they will feel more stable than LT tires.
ST tires shouldn’t be used at speeds above 65mph to limit heat buildup that can cause a premature failure or catastrophic blowout. LT tires are usually capable of handling speeds greater than 100mph without this issue. You can check the speed rating of LT tires to see exactly how fast they are capable of going before speed becomes a problem.
There are situations where a LT tire can be used on a trailer, but generally speaking, light truck tires should be used for light trucks and special trailer tires should be used on trailers.
Can You Put Light Truck Tires On A Trailer?
Light truck tires can be used on 5th wheel trailers but generally speaking, Special Trailer (ST) tires are best for use on trailers. ST-metric tires have better load carrying capabilities and will not sway as easily as LT-metric tires.
Can you put LT tires on a 1/2 ton truck?
1/2 ton trucks will get no benefits from light truck tires since they don’t need the extra load index capacity. They will simply make the ride harsh and less comfortable.
What Are Special Trailer (ST) Tires
Special trailer tires are tires that are specially designed for use on trailers, as you have probably guessed by now. They are constructed very differently from passenger and light truck tires. They are designed to handle extreme weight pressing down vertically and have very little sidewall flex.
They are usually bias ply construction, unlike passenger and light truck tires which are usually radial tire construction to allow for more sidewall flex.
ST tires can not handle speeds above 65mph but there are some that, if inflated properly, can handle speeds up to 75mph.
Trailer Tires Vs Truck Tires
ST tires and LT tires are both designed for strengthened sidewalls, but they are very different tires and shouldn’t be confused.
Trailer tires are great at handling vertical loads but not good at cornering. They also can’t deal with high speeds very well and can overheat easily above 65mph.
Truck tires have stronger sidewall construction than passenger tires but due to their radial design they still have some sidewall flex and are better at cornering making them better suited for use on a vehicle than being simply towed. Truck tires can also handle speeds above 100mph without worry of failure due to heat buildup.
Can You Use Trailer Tires On A Truck?
Trailer tires should never be used on a truck. They may have the load index necessary to meet or exceed the requirements for light trucks, but they have very little sidewall flexibility and have extremely poor handling characteristics. So much so that they would be dangerous in this use case. They also can not handle highway speeds and can overheat and lead to a blowout condition easily.
Can You Put Car Tires On A Trailer?
Passenger car tires do not have the load index and sidewall strength to be able to be used safely as a trailer tire. Trailers need tires capable of supporting much heavier loads. ST-metric tires are best for trailers although LT-metric tires are commonly used in some situations.
What Are Temporary (T) Tires
Temporary spare tires are available as full size, compact (aka donut), and collapsible (inflatable) versions.
Types Of Temporary Tires
Full-Size Temporary Spare Tire
Full-size temporary tires maintain the same rolling diameter as the regular tire it replaces. It is usually narrower and the wheel diameter may differ. Like all temporary tires, they are limited to 50 miles of range at no more than 50 miles per hour.
Compact Temporary Spare Tire (Donut)
Compact temporary tires, also known as donuts, save more space by not matching the rolling diameter. They are designed to meet the bare minimum required to allow you to drive away from the site of a flat and get your tire replaced as soon as possible.
Collapsible Temporary Spare Tire
Collapsible temporary tires are essentially donut tires that are deflated. They require that vehicle manufacturers include a method of inflating the tire. They are usually only included in vehicles that have very little extra room to carry a spare.
Spare Tire Vs Regular Tire
While some larger vehicles carry a full-size matching or non-matching spare tire that is identical to the regular tires they have mounted at all four corners of their car or truck, tires that are Temporary (T) are not designed to be used for more than 50 miles and not designed to cope with speeds greater than 50mph.
They’re designed solely to get you out of an emergency situation until you can get the failed regular tire replaced as soon as possible.
Full-Size Spare Tire Vs Donut
A full-size spare tire takes up more space but will ensure that systems such as antilock brakes and traction control systems will be able to function properly since the rolling diameter of the tire remains the same.
Most full-size spare tires are on larger vehicles that can mount them on a rear hatch or underneath the rear of the vehicle. These are usually just a regular passenger tire and not temporary tires since there isn’t much space savings to be had between a regular tire and a temporary full-size tire.
There are some situations where a full-size temporary spare can save enough space due to the reduced width that vehicle manufacturers decide to include them instead of a standard passenger tire.
Even though it’s full sized, full-size temporary spares are still limited to 50 miles of range at no more than 50 miles per hour.
Donut tires, compact temporary spares, are smaller to save as space. They can interfere with antilock braking and traction control systems since the rolling diameter is not the same.
Below are some links you may find helpful when learning about tires
- What’s so special about ST tires? – Priority Tire
- What’s the difference between p-metric/passenger tires and lt/light truck tires? – Tire Buyer
- Spare tires – Goodyear
- What is the difference between p-metric and metric tire sizing? – Consumer Reports
These broad classifications of tires are very different from each other and on the surface may seem obvious. But we often receive a surprising amount of questions about how they can be used and when they should be used.
Hopefully this article was able to answer all of your questions regarding the different classifications of tires and you feel comfortable knowing when they should be used and how to use them.