GP503, powered by racingreifen. de and operated by Reifen Walter, is a specialist retailer for motorcycle tires, backed by more than 30 years of racing experience. Based in Hilpoltstein, Germany, the business serves riders through an online shop and a local workshop.

Its tire selection includes products from Bridgestone, Continental, Dunlop, Metzeler, Michelin, and Pirelli, with options for road riding and racing. Customers can browse racing slicks, rain tires, profiled racing tires, and road tires, as well as find tire information, technical data, and approvals. The shop also offers tire search tools, motorcycle tire guidance, fitting accessories, gift vouchers, sale items, and information about current manufacturer promotions.

Beyond retail, Reifen Walter provides motorcycle maintenance and inspection services, and customers can arrange a workshop appointment. The company lists its contact details and opening hours online and offers customer accounts, a wish list, and a newsletter. GP503 brings together specialist tire expertise, racing-focused products, and practical services for motorcycle riders