A tire's primary job is to safely carry the weight of the vehicle and passengers. It does many other great things, but this is its most important and most basic role.
Recently, a customer asked for a specific load capacity for the tires on his 2007 Audi S4. He was changing the wheels and rightly noticed that his Original Equipment (O.E.) Continental ContiSportContact 2 tires were XL rated tires. Generally, we recommend staying with a tire that has the same load capacity. This is especially important on 3/4-ton and 1-ton pic up trucks.
However, for certain car applications it may be acceptable to use a standard load tire when an XL tire was O.E. The tire must carry at least half of the gross axle weight rating for the vehicle's heaviest axle. On the Audi mentioned above, the tire needed to carry 1,356 lbs. per tire, because the heaviest axle was 2,712. For his Winter Wheels and Tires, we found that all winter tires in the 17-inch winter size carried more then 1,356 lbs., so the standard load tires were just fine.
I am glad we got a chance to talk though, because it is very important that tires carry enough weight to support the vehicle correctly. Inflation pressure also plays an important role so if there is any question at all it is best to call and make sure your application is safe to use.