Bearings similar to our trailer bearings were a stock item in automobiles up until the 70's-80's when a sealed bearing unit replaced them. Those cars would run out until 100K miles or better, if serviced. If you are replacing with good quality USA or Japan bearings, the service life should be close to 100K mi., if serviced and a majority of miles are on asphalt. Your service schedule is more than adequate (yearly) but a good idea since it allows for an inspection of hub, brake hardware, and bearings. It will also include an adjustment of brakes, which should lengthen brake and drum life.
