At full extension, the chain does pull the rear wheel down when you are on the throttle. If you draw a straight line thru the center of the axle and the countershaft, this line falls below the center of the swingarm pivot. The chain naturally wants to pull the rear wheel towards the countershaft, but it can't because the swingarm holds the wheel in place, so the force is directed in an arc around the pivot. Since the line of force is closer below the pivot than above it, the wheel is forced down. Granted, the wheel is only at full extension when there is no weight on it, like after a bump or jump, so this rarely comes into play. The opposite is true under most conditions. The rear wheel is up in the suspension travel, bringing our imaginary line above the center of the countershaft, causing the chain to pull up on the wheel. Suspension and chassis designers have to take these forces into consideration in the design. The influence of these forces on rear suspension are the reason your valving and spring rates result in the rear suspension working better under power, it is designed this way because you hit most obstacles under power. This is also why manufacturers try to locate the pivot as close to the countershaft as possible, to minimize this force. Eyvind Boyeson developed a rear suspension system that was supposed to eliminate all chain forces on the rear wheel and tried to interest the manufacturers in production, but got no takers for whatever reason, probably the cost, weight, and complexity of his design.
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1992 KDX 250-FMF porting,two-stage power reeds, Fatty pipe, Power Core silencer,titanium rod,Wiseco Ultra-lite, Pro-Action suspension...Why didn't I take the blue pill???