I posted this in another thread but thought the information might be more easily found in it's own thread. The text is a mixed compilation from me, SteveC and Dekots:


Showing how the center of the board moves outward the further down you go.
or conversely, inward as you go upward.
Quote:
Originally Posted by Dekots
I will try and make this easy--make a fist around a ruler at it's middle (or use a small stick) and hold it fingers down right on top of a table. Twist to the left without lifting your fist. The left end digs into the table, the right end wants to go skyward. Now, if this was a truck, it would also want to turn left and rotate with the left side coming towards you. With softer bushings, it would turn easier with less force of trying to turn your wrist to the left because they would flex allowing the turn. Less force to the left means less lift on the right which means more even distribution of force on the tires which means more traction. No matter what, a turn to the left would put more downforce on the left tires and wear the inside tire more. Softer bushings=Less upforce=more force on 4 tires=more grip for slower speeds. Why just for lower speeds? At higher speeds, gravitational forces in the turn play a bigger role. At higher speeds, you kind of have to look at your center of mass and what it's forces are in a turn.

What happens at a turn? Conservation of momentum makes your body want to go straight but you are turning and your tires want it to curve. The higher your center of mass, the more of a moment or turning force it creates at the trucks perpendicular to the axle. This force plays a more significant role at speed. Basically, when you go really fast and you want to turn, we have the bushing dilemma as described above, but we have an additional force wanting to throw us off the board at a right angle so we lean way over which moves our center of gravity to the inside of the turn. This also creates a moment at the trucks which wants to lift the outside tire. When we drop the board, we shift the center of force to the outside of the board countering this moment (see fantastic diagrams posted by SteveC above!). This is why dropped boards at speed turn nicer and slide more predictably--the shifting of the center of force on the trucks shifts towards the outside wheels.


Top mount: Most leanable, most grip (The reason being that at full lean your weight is going to be close to the center of the truck than with dropped boards, meaning that your weight is going to be more equally distributed over the four wheels), most control but this is at the sacrifice of stability for some. Really it just takes strong ankles. Some people don't like the straight deck aspect of these boards because there is no natural foot-stops on either end of the board, that is when your pushing your front foot may want to move forward if you aren't putting enough pressure on it and as your back foot has a tendency to slip back when tucking, you could have problems if your grip isn't grippy.

Drop through: Added stability but proportionally less grip/lean to the change in height of your center of gravity (say in comparison to a topmount). The reason for this is that because of the way a skateboard turns, as you lean you start applying less force down an more force to the side. You have less leverage with lowered platforms:
Quote:
Quote:
Originally Posted by SteveC

What happens when you drop a board is you're reducing the board's leverage over the truck's roll axis (this in turn effects how the bushings behave). It also effects the board's center-line under turn, and the angle from which the rider's inertia and other forces effect the board. (these two effect the weight ballance between the inside and outside wheels)


It also means that you have to put more weight on the edges of the deck to make the turn and that moved the center of gravity of the *rider* more off the center of the trucks than he'd have to move for a top-mount deck to make the same turn.
The drift on anything with a lowered platform is going to happen earlier and be easier to control. Usually this sort of straight deck drop though should have a ride height in between that of a topmount and drop deck. A disadvantage of this is that the nose and tail become noticeably weaker, a hit to a wall can shatter them. The board will still be usable (probably) but torsional flex will increase.

Drop deck: Everything about drop through is applicable here, except the part about fragility. There is the added benefit of front and rear foot-stops.