Hi,

Weight (or more appropriately Mass) is a Factor in Momentum - P=MV... Objects in motion are said to have a Momentum. This Momentum is a Vector. It has a size and a direction. The size of the Momentum is equal to the mass of the object multiplied by the size of the object's Velocity (Speed). The direction of the Momentum is the same as the direction of the object's Velocity. So the more Mass (weight) an object has, the more Momentum it will have for a given Speed...

The Principle does not apply in this case, nor does Unsprung Weight, so far as Acceleration is concerned, Weight is Weight... period.

Acceleration is a Vector quantity which is defined as "the rate at which an object changes its velocity." An object is Accelerating if it is changing its Velocity. It increases it's Velocity by adding more Force from the Engine. By reducing the Overall, not just Unsprung, Weight, resistance is overcome more easily leaving additional Power to make the Car go even Faster.

Unsprung Weight is the Mass of the Suspension, Wheels and other components directly connected to them, rather than supported by the Suspension. (The Mass of the Body and other components supported by the Suspension is the Sprung Weight.)

Unsprung Weight includes the Weight of components such as the Wheels, Spindles, Wheel Bearings, Tires, and a portion of the weight of Driveshafts, Springs, Shock Absorbers, and Suspension Links. If the vehicle's brakes are mounted outboard (i.e., within the Wheel as is the Boxster), their weight is also part of the Unsprung Weight.

The Reaction Forces of the Wheels to bumps and surface imperfections are transmitted by the Suspension to the Body. The greater the Unsprung Weight, the larger the forces exerted on the Body. Therefore, the smoothness and stability of the Ride and the Mechanical Loads are closely related to the ratio of Unsprung Weight to Sprung Weight.

The Inertia of the Unsprung Weight affects the Suspension's ability to follow the shape of the Road, or Track. As a result, high Unsprung Weight has a negative effect on overall Handling and Braking ability, especially on imperfect surfaces. This results in having to traverse this Road at Lower Speed to keep control of the Car, you cannot allow the car to go as Fast as if the ratio of Unsprung to Sprung Weight were more favorable.

Sorry, I did take a lot of Physics, it was my minor...

Happy Motoring!... Jim'99

I agree with denverpete and don't really care to see the facts, the comparisons or the history thereof. Rather I think it's nice to see the opinions resulting from the release of adrenaline/epinephrine (or dihydroxyphenylmethylaminoethanol for those historically minded souls who want to avoid using "propriatary" names). Liked the pics. Good luck getting enough $$

I think what 99-Boxster-MK is thinking of is that the diameter of a wheel can affect the acceleration of the car. People that plus-size their wheels can see a small effect on their 1/4 mile times for instance.

This is because of the bigger wheel usually being heavier than the smaller wheel, and the weight being distributed further out along the axis of rotation.

However, if you're really seeing a decrease in performance because of a slight increase in wheel weight and diameter, the problem is likely that your car is severely underpowered. It's more of a 100-150 HP car problem than a 240 HP problem.