Will there be any problems if I forgot to do a tire rotation on my mazda 3? I seem to have gone past 19000 km without ever rotating the tires. If I rotate it over the weekend, will there be any problems whatsoever?
19000 km is nothing. I got rid of my 2011 Toyota Yaris at about 80000 km on the odometer, 40000 km on the summer tires and 40000 km on the winter tires. Both tires had plenty of tread left, although an alignment problem caused an unlucky tire that was on the front right two times in a row to wear unevenly. If you drive carefully, I would say that top-quality tires can easily last 80000 km, if there's no alignment problem.
I would however after 19000 km recommend you to rotate the tires for the first time. I live in an area where winter tires are mandatory and thus tire rotation happens naturally twice during a year. If I lived in an area where winter tires are not needed, I would probably choose about 10000-20000 km as the rotation interval. Of course, rotation at 5000 km would in theory allow slightly better tire life due to more even wear, but I don't think it's worth the trouble. After all, your time has value as well.
No problems, as long as the tires still look pretty evenly worn. If the fronts or back look oddly worn, it may be time for an alignment, and you may need replacement tires.