I was thinking of going 20's all around or just in the rear. If I stick with 30 series tires and get forged lightweight rims will the 20" circumference still hurt acceleration? And if so, would it just be negligible?

 

Weight is what hurts acceleration...and rotating weight hurts acceleration more than static weight. It's a general rule of thumb that if you take 100lbs (static weight) off your car you will go 1/10th quicker in a 1/4mi race. It's also a general rule that 10lbs of rotating weight is equal to 100lbs of static weight. So if your new wheels are 2.5lbs a piece more than stock, you will slow down 1/10th of a sec in a full 1/4mi run. If we ditched the stock 28lb wheels and went with some light weight 17" wheels that were around 10lbs lighter we would get about 40lbs weight reduction and at that point you could actually FEEL the difference. Most people can't feel the difference between a 15sec run and a 15.1sec run.

So, you will go slower, but it won't be perceptible to you.

 

The rims I'm looking at are 19x8 and 22lbs and 20x10 and 27lbs. So the rear wheels on the SRT6 are 28lbs? I guess I would be saving some weight in that case. So the slight gain in circumference won't hurt acceleration any then?

 

well physically, a larger diameter would mean faster because the farther you get from the hub the faster the movement of the outside would have to be..

make sense?

but i dont think thats holds true for cars because of weight issues. but since its lighter, i would assume there would be no loss at all. im no expert though

 

If you increase the tire height (larger circumference) it's basically like putting a "higher gear" in your car.
Your car will actually travel faster at a lower RPM.
Increasing the tire height by as little as 1" would make your car perform more like a car with a 2.90:1 rear end instead of a 3.07:1 that you currently have.
For acceleration, this is not good.
If you go to a 20" tire in back, and use the 30 series tire (like you mentioned), you will retain the approximate tire diameter you now have with the current 19" by 35 series. So all things considered, your performance should stay the same.

 

Don't forget the weight of the tire as well...with rotating mass, the radius at which the mass sits is very...what that also means is a larger diameter wheel can be worse than a smaller one even if it's the same overall weight...just because you've moved the mass further from the axis of rotation (think about a skater speeding up or slowing down a spin by pulling extremities in or pushing them out...overall mass doesn't change, but the speed of the rotation sure does)