In 1976, the Japanese firm Tamiya, which was renowned for their intricately detailed plastic model kits, released a series of elegant and highly detailed, but mechanically simple electric on-road car models that were sold as "suitable for radio control". Although rather expensive to purchase, the kits and radio systems sold rapidly. Tamiya soon began to produce more purpose-built remote-controlled model cars, and were the first to release off-road buggies featuring real suspension systems. It was this progression toward the off-road class that brought about much of the hobby's popularity, as it meant radio-controlled cars were no longer restricted to bitumen and smooth surfaces, but could be driven virtually anywhere. The first true Tamiya off-road vehicles were the Sand Scorcher and the Rough Rider, both released in 1979, and both based on realistic dune buggy designs. Tamiya continued to produce off-road vehicles in increasing numbers, featuring working suspensions, more powerful motors, textured off-road rubber tires and various stylized "dune buggy" bodies. They also produced trucks, such as the Toyota HiLux Pickup, that featured realistic 3 speed gearboxes and leaf-spring suspension systems. All of these models were realistic, durable, easy to assemble, capable of being modified, and simple to repair. They were so popular that they could be credited with launching a boom in radio-controlled model cars in the early to mid 1980s, and provided the basis for today's radio-controlled car market. Popular Tamiya models included the Grasshopper and the Hornet dune buggies as well as the Blackfoot and Clodbuster monster truck models. The earliest Tamiya models, particularly the early off roaders, are now highly sought after by vintage R/C collectors and can fetch prices of up to US$3000 on internet auction sites if still in mint, unbuilt form. Acknowledging their continued popularity, several of the early kits have even been re-released by Tamiya during 2005–2007, with a few alterations. A British firm, Schumacher Racing, was the first to develop an adjustable ball differential in 1980, which allowed nearly infinite tuning for various track conditions. At the time the majority of on-road cars had a solid axle, while off-road cars generally had a gear-type differential. Team Associated followed suit with the introduction of the RC100 1/8 scale gas on-road car, RC12 1/12 scale on-road electric car, and RC10 in 1984 (see below).