Hi Dodo;
the reason why the spring rate is higher at the front compared to the rear is the different motion ratio that both ends suspensions have. At the rear the ratio is about 1:1 which means that the wheel movement as it moves upwards or downwards is the same as the amount of movement of the spring, so for each inch of wheel travel you have the same amount in inches of spring deflection. This means that the effective spring rate (wheel rate)at the tyre contact patch is the same as the spring´s one.
However, at the front, the motion ratio will be around 1:0,5 which means that the wheel travel is almost the double of the spring deflection and this means that you will be having around 25% of the spring rate as wheel rate.
The actual suspension stiffness is the wheel rate so this means you have a softer suspension at the front than at the rear, even with stiffer springs at the front than at the rear (just a matter of leverage). This also is in connection with the weight suspended on the front axle and on the rear axle, which is different, being around 40% at the front and 60% at the rear, hence the highest resistance needed for the rear axle compared to the front.
hope this helps.
cheers.
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