It is based on the Z4 Concept unveiled a year earlier, and was developed alongside the fifth generation of the Toyota Supra due to BMW's partnership with Toyota.[5] It is based on the Cluster Architecture platform and has a 50:50 weight distribution with weight savings of up to 50 kg (110 lb) as compared to its predecessor.[6] The soft-top convertible roof returned on the Z4 (G29) instead of a retractable hardtop.