ORIGINAL: bigbulls

Because a 70 pound limb has a specific spring rate. That is it's optimal rate of bend. That is where it was designed to have peak performance.

When a limb is shot at its max draw weight that limb is pre stressed, or pre bent, in a manner in which it was specifically designed to be stressed.

When you back out the limbs you are removing some of this pre bend in the limb so it can not perform in its optimal spring rate.

It's kind of likeleaf springsor truck. Limbs are basically large, flat springs made from fibers.
Those springs are designed to have a cerrtain ammount of weight and stress applied to them to get the best performance from thatspecific set of springs. If you have a spring that is designed to have 5000 pounds (70 pounds limbs)of compression to operate optimally and you are using them in a vehicle that only is able to apply 3000 (turned down to 60 pounds)on them then they are not going to give the driver a very smooth ride.

I hope i didn't just confuse everyone. [&:]