"Around 1930, Sloan considered the problem of ride quality as one of the most pressing and most complex in , and the problem was getting worse as car speeds increased. The early solid rubber tyres had been replaced by vented thick rubber, and then by inflated tyres. In the 1920s, tyres became even softer, which introduced increased problems of handling stability and axle vibrations. On a trip to Europe, Sloan met French engineer who had patented a successful independent suspension, and had him visit the US to make contact with GM engineers. Also, by 1933 already had an independent front suspension, which was on cars imported to the USA. , who had previously worked for Rolls-Royce, was employed by GM, and worked on the introduction of independent suspensions there. In Sloan's autobiography, a letter from Olley describes an early ride meter, which was simply an open-topped container of water, which was weighed after a measured mile at various speeds. Rolls-Royce had been looking carefully at ride dynamics, including measuring body inertia, trying to get a sound scientific understanding of the problem, and Olley introduced this approach at GM."