Just like Edgar said, grab the left rear wheel in your left hand and the right rear wheel in your right hand. Take you right thumb and while holding the tires to prevent them from turning, try and move the spur gear. The goal is to get the diff spinning as loose and free as possible while not being able to move that spur gear with your thumb. Now for asphalt, you may want to loosen the diff just a little to help prevent breaking the rear tires loose as asphalt, most of the time, will not have the same grip as carpet.

As for settings and not knowing how much grip your asphalt track has, I would start off with the following set up. This would be for a very low bite, asphalt track:

• soft T bar (1.75),
• the softest center spring on the center shock,
• 20 weight oil in both shocks,
• medium to hard front springs,
• wide front track and
• the narrowest rear track you can get.
• Use the 5 degree reactive caster blocks (the 0 degree blocks smooth out the car more but can be difficult to mount some of these new bodies.)
• Make sure the body fits loose on the body posts. This frees up the chassis.
• I like the long upper arm position on the front end as it reduces camber gain
• Depending on how bumpy your track is, start off with about 4mm ride height in the rear and 3.5mm in the front. More if the track is extremely bumpy.
• Pink rears
• Purple fronts (as the rear bite comes up or if car pushes, use magenta fronts or double pink fronts)
• True the rear tires down to about 48 or 46mm and the fronts with a 2mm split from the rears.
• 1mm negative camber
• Lots of caster
• .5mm rear pod droop.
• Batteries in the forward position

If it pushes then you can narrow the front track, put softer front springs or harder center, shock spring, and widen the rear track. If the car pushes, then it's easy to get more steering but not always easy to get rear grip. Make sure the car is not tweaked and go have some fun. The S120 is a very good car.