We use stainless steel wheels to prevent problems. The wheels have sealed bearings for maintenance-free use, they operate quietly, smoothly and, contrary to what our competitors say, they do not wear the track. We have bifold doors that have been in our showroom for over 3 years and the doors still run as smoothly as the day they were installed (bearing in mind that our showroom bifold doors have been opened and closed approximately 20 times every day for those years).