Gymkata

I just found my new favorite website for now. I don't think it has been posted to the ISF forum before. It does the best job I have seen on a website in explaining and helping you to calculate how different wheels and tires will affect rotational inertia and what that means to the way your car drives. I thought it was a great read and had useful tools, even though I only understand about half the math on the site...ENJOY.

http://hpwizard.com/rotational-inertia.html

ERDoc74

interesting! good find..... maybe this will quite some of the debate about heavier/lighter wheels..... (difference is likely negligible....)

MisterSkiz

iTrader: (2)

This is why i fill my tires with Helium.

ERDoc74

LOL... Too funny!

lobuxracer

iTrader: (2)

http://www.caranddriver.com/features...d-tires-tested

This is a lot more practical and includes actual test results on a real car.

Gymkata

That is a good one. I remember reading this article when it came out. I had forgotten about it.

Just F Me

I'm sure it's good stuff...once I saw the formulas and equations, I closed it.

Dawa

iTrader: (5)

i think the more important thing here isnt that bigger wheels reduce acceleration speeds/time, but that they REDUCE the time/distance it takes to come to a complete stop.

VtotheJ

iTrader: (2)

Articles like this make me glad that I didn't upsize tire widths when I got my tires. I've said this before, but I really want to see timed results and comparisons between stock sizes and upsized tires on the same track.

Gymkata

I have a quick question for anybody that knows the answer:

Does lowering unsprung weight make the car ride feel firmer/stiffer overall, or does the lightened weight just help the springs rebound after compression more easily/faster (& thereby making handling on rough surfaces better)?

My guess is that it does not make the ride firmer because the sprung weight did not change and so spring compression should feel the same, but spring rebound will be better and the car will better handle uneven surfaces. Of course I imagine the change would be very subtle unless there was a drastic change in unsprung weight.

(I know that this stuff doesn't make a drastic change in performance, but I figure that there are a few experts here who can correct any flaws in my logic. I just like making sure I understand exactly why something does or does not work, even if understanding the concept doesn't greatly affect how I drive my car.)

lobuxracer

iTrader: (2)

Lighter wheels have better compliance with the road surface which tends to improve traction over rough surfaces. They do not make ride feel stiffer.

zmw

I'd be more interested in seeing a reduced weight upsize versus stock - my 20" TE37s with tires weigh less than the 19s with 245/275 combo.... but frankly, the ISF isn't a race car, and it gets pretty bad gas mileage even in stock trim so I'm not sure it'd sway me one way or the other.

lobuxracer

iTrader: (2)

Bad gas mileage compared to what?

zmw

well, that's a fair question, for a 416hp sport sedan, I suppose it's not bad... and on the freeway during road trip mode it averages about 23, so that's not terrible - then again i've had tanks where the average is like 13 ;P

lobuxracer

iTrader: (2)

My worst is 5.3. Best is 28.7. I usually get 26 - 28 highway on long trips as long as I don't have the bicycles on the back. I've never thought it was bad gas mileage, even the 5.3 is easily explained - track weekend mileage.

23 sounds a bit low compared to what many of us have posted for highway mileage.

Besides, I wouldn't really care if lighter wheels brought better mileage - I'd like better acceleration in low gears and better suspension compliance so I don't have to lift going around corners with bumps.