Northwest GT

Well, let's look at the difference in rotational inertia between a lightweight aluminum driveshaft with a larger radius and an OEM Ford steel driveshaft. Remember the weight ratio between these two shafts is more than 2:1 (and the mass ratio is the same). The difference in diameters between the stock shaft and the Powerhouse shaft is about 3'' vs 4''. When you take the radius squared the ratio is less than a factor of two (2 squared vs 1.5 squared). So, the reason you gain in terms of reduced rotational inertia when you switch to the aluminum shaft is primarily because of the mass reduction. In other words, the aluminum shaft is lighter and easier to spin up (angular acceleration). Doesn't use up as much HP and Torque. And, most importantly, as the other guys have already said. You will go a little faster

metroplex

It'd be interesting to work with actual numbers just to see the difference. I believe you, but I'm not convinced enough to start messing with the stock driveshaft that is supposed to work vibration-free up to 145 mph. One thing I learned about driveshafts is that if it ain't broken, don't fix it.

Rebel73

well, I'm not sure about the ds yet, but I am looking into some lighter wheels, 20 or less lbs.
They are definately pricier, but I find the prospect of going a little faster by reducing weight very attractive.

What do you guys think of these?
http://www.tirerack.com/wheels/Displ...Silver+Painted

They are 20 lbs. for the 18s, and the 17s are about 18.5 lbs. I think.

metroplex

The moment of inertia for a hollow tube is

I = 0.5 * Mass (in kg) * (R1^2 + R2^2) where R1 is the radius from the axis to the inner wall (in m) and R2 is the radius from the axis to the outer wall.

Basically R2 is just the radius of the driveshaft and R1 = (R2 - thickness of wall).

Using these assumptions:
Alum shaft = 20 lb, 4" diameter, 1/4" thickness
Steel shaft = 40 lb, 3" diameter, 1/8" thickness

I got something like a 14.6% reduction in the moment of inertia going with the aluminum shaft.

07GT_BLACK

I love the SSR Comp wheels and they are so light....Does anyone know the price???? I found these images on tirerack.com, but no price is listed.

http://www.tirerack.com/wheels/Displ...e+w%2FMach+Lip

Poco

This a strange but real world topic.Would the initial question depend on your car as well?The rotative inertia on acceleration can depend on factors like the gearbox ratio,rear end ratio and total weight of the car.Less rotative inertia will perform and accelerate faster.Is the mass of the wheel in the center or towards the ring of the rim? And nots forget about tire weight.That can affect or in fact enhance the balance of the combined tire & wheel.Another factor would be the load on the bearings the wheel rides on.Is the wheel true?If the wheel were off by a few degrees on it axis that could lead to a load on the bearing and cause premature failure.
I like the new style larger rims but do the wheel manufacturers realize or even consider the applied application.I really hate seeing wheels fall off or axles come off on the hiway.
I saw 26" wheel the other day and couldn't beleive that any thing but maybe Hummer could roll these monsters.Sorry to rant.Pat

Rebel73

You sure know how to pick 'em!


SSR Comp-H
19x8 $249
19x10.5 R$459
19x8.5 $389
19x10.5 R$459
19x9.5$529
19x10.5 R$459
19x8$249
19x9.5 R$529
19x8.5 $389
19x9.5 R $529
19x9.5 $529
19x9.5 R $529