If we had the perfect springs for the person on a bike
both front and rear what would be the static sag front and
rear?just the weight of the bike with no rider on it.
overbore
The perfect sag is the sag that works best for the rider. I'm sorry if that's a cop-out answer, but it is the truth.
As a rule of thumb, you want about 100mm of static sag at the rear and about 35mm at the front. Every rider is different, so try different settings and remember to write down what happens at certian settings.
25mm static in the front is the best preset. You can use more or less to fit your taste, but you cant go wrong with 25mm.
25mm on the rear (set race sag at 100mm just for this test) is the best starting point. Although anywere from 20 to 30mm will do alright, but they will provide a slightly different feel . After taking the static sag reading be sure to set your race sag back to desired setting.
Because of stiction it can be hard to measure static sags. Its best to lift the bike then let it drop easy on its own weight, take the measurement... then push down on the bike and let it lift on its own then take the measurement.... the middle of them two readings is the acurate static sag reading.