Do you have one of these sizes? If so, you must own a GM vehicle. It appears these sizes were made by GM for the Buick Enclave, Chevy Traverse, GMC Acadia and Saturn Outlook. That being said, there aren't many options available in this size, however there are more options now than a year ago.
Since these vehicles have been around a few years, it's probably time for many owners to think about changing tires.
Beginning with the 18" size, the O.E. Goodyear is not a bad tire, but I believe the Continental CrossContact LX20 with EcoPlus Technology (pictured) would be an upgrade over your current tire. This tire has good all-season traction, is relatively quiet and features Continental's low rolling resistance technology. This means that you should experience an increase in fuel economy. The other tire I would suggest is the Goodyear Assurance CS TripleTred All-Season. This tire has a more aggressive tread design and will perform better in the snow and rain versus the original Goodyear. Typically, these replacement tires are offered at a lower price compared to the Original Equipment tire.
As for those SUVs with the 19" size, the O.E. Michelin is also a good tire, but tends to be more expensive than some other options, while the Goodyear Eagle RS-A leaves much to be desired and suffers in many performance categories. The first tire I would suggest is the Bridgestone Dueler H/L Alenza. This tire is quite comparable to the Michelin, but at a lower price. It has good all-season traction and is also relatively quiet. Another exceptional value option would be the Firestone Destination ST. This tire features a unique and stylish tread design that performs quite well in wet and dry conditions.