(from John Pierce on the Beeeg List)

find out your bikes full suspension travel (published in the specs at various sites, www.bmwsantacruz.com has them in their new motorcycle listings)...

you want the 'preload' with your weight on the bike to be about 25% of the full travel. measure this as follows... centerstand the bike, and have a friend measure from each axle to a point directly above it. then put the bike on the wheels, sit on it in your normal riding position with just tiptoes to balance and have the friend make the same measurements... the difference between the first and 2nd is the preload... adjust the spring tension to get this around 20-30% of your full suspension travel. If your shocks have hydraulic preload adjusters, I'd suggest backing those all the way out (softest setting, most sag), then set the spring preload with a "C wrench" to the softer side of the range, say 25-30%, so that the limited range of the external preload knob is most useful (for instance, you can crank down on it when you are carrying an extra heavy load or passenger)