Originally Posted by 1killer1liter
Hmmm. When mine was 2 1/2" lowered in the rear and stock up front, it turned extremely fast. There is another thread on raising the front and leaving the stock height out back to get faster turn in. Same thing.
Well, lowering the rear will add trail, thus adding stability at the expense of steering quickness. Lowering the front will reduce trail, decreasing stability (but lowering CG, which is why drag racers do it). For maximum straight line stability, you'd theoretically want as much trail as you could get. I say theoretically because there's a lot of variables to balance.
As for tire swaps, some tires have a taller profile or aspect ratio than others, and some have rounder profiles than others. It all makes a difference. Taller in front gives you more trail (because it raises the front). Taller in back gets you less trail.
Racers typically decrease trail over stock by lowering the front end (raising the fork tubes in the clamps), raising the back end (less common), using a rear tire with a taller aspect ratio than stock, or some combination thereof. Of course, then you need a steering damper to stabilize the bike. Fancy rigs will have adjustable swingarm pivots (for changing anti-squat, etc.) and adjustable steering offset.
Another factor that affects front-end stability is the wear pattern on the front tire. A squared profile will have a natural oscillation frequency much lower than a round tire. The engineers will typically set up the bike so that the natural oscillation frequencies are high enough to be damped out naturally.
Sidewall stiffness also makes a big difference, just as underinflating the tires will destabilize the bike.
Sooooooo many variables. It's no wonder the top racers always bring their crew with them.
This is a quote from Captain Jack, a member here.