Buying a new set of tires first means choosing the brand you want, getting the right size, then having them installed. But some drivers prefer to buy oversized tires, due to a vehicle modification, or just because they like the look. For drivers shopping at Costco, where there are perks for buying tires, they may be out of luck. That’s because Costco tire centers will only install tires that match manufacturer specifications.

Costco cites safety concerns as the reason for this policy, which recommends that customers know what they need beforehand. Not only must the tires be the right size, but they must also have the same or greater Original Equipment (OE) Speed Rating, if existing tires carry a rating. The speed rating of a tire refers to the top speed a tire can safely maintain under specific conditions. Tires also need the same or greater OE Load Index as existing tires as well, which is the maximum amount of weight a tire can support when it’s properly inflated.

Some customers may prefer to install tires themselves, but Costco’s ordering system must still be used. When selecting tires online , users enter the make, model, and trim of their vehicle. Matching sizes offered by available brands are displayed and the purchase price typically includes installation. When tires are shipped to a local Costco Tire Center, a representative will verify that the tires match the vehicle. If there is a mismatch, Costco may not move forward with installation.

Using oversized tires can be a stylistic choice that some drivers want, but there are a number of problems that can occur. It begins with perhaps the most important factor: driver safety. Running the wrong size tire can prevent a vehicle from performing as it’s designed to do, which can make for a dangerous situation. This includes braking distance, steering response, and the overall stability of the vehicle.

Then there’s the issue of reduced fuel efficiency, as bigger tires affect MPG. They usually add weight and increase rolling resistance, causing the engine to work harder to keep the vehicle moving. That means more trips to the gas pump, which can get very expensive. 

Using oversized tires can also cost drivers more money beyond the pump. That’s because some vehicles require a lift or leveling kit to create the necessary clearance. This can lead to alignment problems, which can cost even more money later on. Larger tires may also require new rims, along with adjustments to systems like the speedometer, or the existing tire pressure monitoring system. Insurance rates can be affected, and vehicle warranty coverage may be impacted if the tires contribute to any claims due to mechanical problems.