Steering wheel inertia

Remembering the past of my experiences, on Volvo 244 GL, the steering stability was lost remarkably soon after replacing the original steering wheel into a smaller & lighter genuine leather covered GT model's one. So, the steering were replaced as they were. The reason for the unstable condition while straight running was due to the reduction of reduction of diameter from 400mm to 360mm so I thought, but, the factor of the weight of wheel itself might have been an important factor that could not be overlooked on earth? Physiologic standing point of view, Inertia phenomena factor should be focused when some dynamic movement is considered? Comparing the weights of two wheels set in BC7 SUBARU Legacy LSi US model, MOMO 3 spokes on a genuine boss and original 4 spokes, remarkable weight differences between them that should not be overlooked. Now, I determined to replace them into original condition. Recent experiment has revealed that BC7 has some innate bad habit, unstable steering action while straight running caused by lack of caster value in frontal axle construction, rising up to the hill is stable, on the other hand, downing is unstable, in addition, fulfilled fuel tank brings stable condition because of tail down and more caster angle is obtained and becoming unstable in proportion to the fuel reduction. In order to gain more frontal caster angle, frontal axle main bar moving forward is one of a choice to be considered, but before that, I would like to replace steering wheels into more heavier original one to rely on the Inertia phenomena for more whee stability.