This is an upgrade option to sand the tires provided with wheel sets. 3D printed hard resin tires that have not been sanded will have imperfections on the backside where the support structures were attached. The sanding process involve filing/sanding the backside to remove divots/nubs, sanding the outside diameter, and sanding the frontside, then buffing for an even finish. Please choose the correct option for your wheel set (either 4 or 6 tires) and if you have ordered multiple wheel sets that require sanding remember to set the quantity accordingly. If you order multiple wheel sets and only one sanding service, we will have to contact you to find out which set needs sanding. Please allow up to 3 business days for your order to ship when adding this service.