Buying Tires Online: Check the Fit, Then Plan Installation

Start with the tire placard, not the old tires

The tire placard is the most reliable fit information on your vehicle. On newer vehicles, federal rules put it on the driver’s door jamb, usually the pillar the door closes against, and in some cases on the edge of the driver’s door. Older vehicles may have it on the glove box door or inside the fuel door. According to the U.S. Tire Manufacturers Association (USTMA), the placard lists the size of the tires the vehicle came with, including the spare, and the recommended cold inflation pressures for the front, rear and spare tires.

Federal rules require the tire size on the placard but make the load index and speed rating optional, so check the owner’s manual for anything the placard leaves out. Then compare it all with the tires on the car now. A previous owner may have switched sizes, so the old tires can point you the wrong way.

Two setups need extra attention:

• Different sizes front and rear. Some vehicle makers specify one size for the front axle and another for the rear, often called a staggered fitment. The placard lists both, and you need the right number of each.
• Light truck tires. If the size includes “LT” (at the start, or at the end of flotation sizes such as 35×12.50R20LT), the vehicle maker called for light truck tires. USTMA says never to mix passenger and light truck tires on the same vehicle.

Read the size, load index and speed rating

A complete size looks like P225/65R17 100H. P marks a passenger tire, 225 is the width in millimeters, 65 is the aspect ratio (sidewall height as a percentage of width), R means radial construction, and 17 is the rim diameter in inches. The 100H at the end is the service description: 100 is the load index and H is the speed symbol, which stands for 130 mph.

Those last two codes are easy to skip, and they matter. USTMA’s replacement guidelines say:

• Never choose a replacement tire with less load-carrying capacity than the original size at the placard pressure.
• Choose a speed rating equal to or higher than the one the vehicle maker specifies. If the replacement is rated lower, the vehicle’s speed has to stay within that tire’s rating.

Many online listings include a list of vehicles a tire “fits.” Use it as a shortcut, not a guarantee. Trim levels, model years and option packages can change the original size, so when a listing and your placard disagree, go with the placard. Start in the right category, such as passenger car tires, SUV and crossover tires or light truck tires, and then match the exact size and service description.

Decide how many tires to buy

USTMA’s preference is to replace all four tires at once, and it recommends that all four have the same size, load index, speed rating and construction. When four isn’t practical:

• Buy in pairs. USTMA recommends matching tire size designations in pairs on an axle.
• Put the new pair on the rear axle, unless your vehicle uses different sizes front and rear. USTMA and major tire makers advise this. Deeper tread grips better and clears water more effectively, and having that grip at the rear helps keep the back end from sliding out on wet roads.
• Check the owner’s manual first on AWD and 4WD vehicles. A new tire has deeper tread, so it is slightly larger in diameter than a worn tire of the same size. USTMA warns that on these vehicles even small differences in outside diameter may cause drivetrain damage, and some vehicle makers advise against replacing fewer than four tires.

Run through this checklist before you add anything to your cart:

Line up a tire shop before you order

New tires have to be mounted on the wheels and balanced, and USTMA says only specially trained people should mount tires. If your vehicle has a tire pressure monitoring system (TPMS), the sensor may be attached to or built into the valve. That is all work for a tire shop, so call one near you before you order and ask:

• Do you mount tires that customers bring in? Shops set their own policies, so ask before you place the order.
• What do mounting and balancing cost per tire, and what does that include? Ask whether valve stems, TPMS parts and disposal of your old tires are part of the figure.
• Will you install new valve stems? USTMA says snap-in valves should be replaced whenever tires are replaced and never reused.
• What does TPMS service involve? When new tires go on, USTMA recommends replacing all the parts in the sensor’s valve replacement kit. It also warns that the system won’t work if a TPMS valve is swapped for a plain one.
• Can you check the alignment? USTMA explains that misaligned wheels stress tires as if the car were always cornering, which causes fast, abnormal wear. If your old tires wore unevenly, have the alignment checked before the new ones start wearing.
• Will you tighten the lug nuts with a torque wrench? USTMA recommends a torque wrench for final tightening, to the vehicle maker’s specification.

If your wheels have locking lug nuts, find the key and bring it to the appointment. The shop needs it to take the wheels off.

What happens after you order

Simolary processes orders in 1–2 business days, Monday through Friday, and offers free shipping to the contiguous US. Orders ship with UPS, FedEx or DHL, and the tracking number is emailed to you once your order ships. You can check its status on the Order Tracking page.

Delivery times are estimates, so the simplest plan is to book the mounting appointment once the tires are in hand, or to keep the booking flexible. Four tires also take up a lot of room, so plan how you’ll get them to the shop.

Check the tires before they’re mounted

As soon as the tires arrive, look over each one before it goes anywhere near a tire machine:

• Size and service description. Compare the sidewall with your notes: size, load index and speed symbol.
• Type. Passenger or LT, matching what your vehicle calls for.
• DOT date code. The last four digits of the DOT code show the week and year the tire was made. A code ending in 3825 means the 38th week of 2025.
• Condition and count. Look for any damage from shipping, and make sure the quantity matches your order.

Do these checks first because of how returns work. Simolary accepts returns within 30 days of receiving the order for items that are unused, undamaged and in the original packaging. Return shipping is paid by the customer unless the item is defective or not as described, and the details are on the Return and Refund Policy page.

If something doesn’t look right, get in touch before you take the tires to the shop. Customer service is available Monday through Friday, 9 AM to 5 PM Mountain Time, at +1 307-215-1213, at support@simolary.com, or through the Contact Us page.