yes, unsprung weight makes a big difference...
so if you have to go large, go forged

 

Right! Lower profile tire weigh less. period. Many tires weigh as much as a wheels do. Most people forget that small fact. Lower aspect ratio = less rotational mass in the tire. It should even out. And PS: I don't think factory wheels weigh 22 lbs. The 17's weigh about 25 to 27 not 22.

 

From Newton’s second law, if total mass of an 18” wheel/tire combo is the same as that of a 20” wheel/tire combo, the angular acceleration of the 20” combo will be less because the distribution of mass is farther away from the center (because of the higher moment of inertia which is a function of radius).

In short … it will take more torque to spin up the 20” combo at the same rate as the 18” combo simply because the mass moved outward.

To determine how much added torque is needed will require me to pull out my physics books which ain't happening.

 

^exactly. ROTATIONAL weight is huge compared to regular car weight. more power needed to turn the wheels before you even worry about the weight of the car.

oem 19s weigh ~22lbs.

 

You are forgetting about rotational inertia. Even if you have 2 wheels that weight the same, the larger diameter will slow you down a lot. Think of a yoyo. When the string is short, you can spin that f*cker really fast. But when the string is long, it takes a lot more effort to get that yoyo going.

 

Look at the big brain on Brad. Pulp fiction.

The point I see overlooked in this agrument is, the outside diameter of the wheel and tire combo is the same for an 18 inch wheel/tire as it is for a 20 inch wheel/tire combo. 26.7" + or - .1, it's not 18" vs. 20". If that were the debate you'd be right. The outside diameter does not change it's 26.7 inches, when a tire is mounted.

You'd have to do a test of two comparision wheel/tire combos to get a winner. A Goodyear Eagle F1 GS-D3 in 225/55 17 weighs 26 lbs. A 245/40 19 weighs 25 lbs. This tire is also wider, which is one of the reason the overall weight might go up, most people install wider tires when upgrading. If you could find a 225/55 17 and compare a identical brand/model in a 225/40 20 the 20 inch tire only would weigh 2.5 to 3 lbs less. This means less rotation weight farther away from center. If you buy a lighter wheel AND lighter tires you will put more power to the ground. I races BMX and Road bikes in my youth so I understand the benefits of having light weight wheels. Heavy a$$ wheels and tires put much more work on your legs. 20's can be lighter but they are not many times.

PS: There are no 19" OEM wheels for the sedan. They are 17" or 18" so those 22 lbs forged OEM coupe wheels do not factor into this debate.