Thanks for taking the time; although you ended up writing almost the same thing I did! "...it is a fact that in every performance aspect, lighter is better, and a 19 inch wheel is better than 20..."
Besides power, higher unsprung weight affects negatively steering, braking, and the suspension/coilover system. If you dig enough on www.rennlist.com, I am sure it's posted there somewhere.

Please note my argument is not about anyone is wrong for getting 20, or if any particularly driver feels or does not feel the difference, or if a dealer is wrong for selling 20's. Just that when it comes to performance...

 

For sure I just could't swallow the the high HP increase. Reason I am so interested is because I am converting my Evo into a race car and want to get the most out of it. I agree with you but saw the numbers a little high.

I feel we are getting off topic and apologize to the person that started the thread, but it's not every day you get to go back and forth with people that have your knowledge cannga.

 

Apart from the fact that my HRE P40 wheel/tire combo adds about 1lb of unsprung weight per corner, the other thing I noticed the moment I put my 20s on was a difference in handling. I felt the turn in to be less sharp (more push or understeer). I feel that it has accentuated the already "soft" or somewhat "sloppy" stock handling (compared to previous 993C4S with eibachs).

My next step is to put coilovers, sways and links coupled with a proper alignment to dial in some more precision.

Oh yeah, and the unsprung weight disadvantage was handled by my Switzer mods.

 

We wrote the same thing, because mathematically it's true. Just like 1.001 is a larger number than 1.0.

The part that bugs me (as an engineer) is that the cited article is very misleading (I found the original on google by the way: http://www.tezta.com/feature.htm ) As I had guessed, It's written by the wheel manufacturer, and they pretty much pull off a smoke and mirrors act on the reader.

First they present all the equations, But then, when the reader's eyes are glazed over from all the math, they fail to actually plug in the numbers in the correct way; and present the results based on an "old tuning rule of thumb". Bul$h1T !!!

As an engineer it just rubs me the wrong way to see this.

Anyways... That's my rant. Carry on!

 

I agree with Can twice in the same day !!!!
I dislike 20's.

In just a few words
Buy a high performance car to change the driving dynamics in favor of bling ? That's 20's .

I don't even find them attractive bling because to me they look gawdy and ill fitted . More importantly they compromise performance and hinder driving .

They serve no purpose on a car of this caliber other than to be seen by those who would be atrracted to it .

 

^I agree...I'm not a big fan of the 20's dog (tongue in cheek). They started out on SUV's and have made their way onto everything.

J

 

Larry, I know if I keep talking, "it" is gonna happen one of these days!

Re. large wheel, one of the threads here has a car with Moton and 20 inch wheel. It's a free country, and I try not to be critical, but freakin' Moton with 20? Oh dear.

 

guys - many thanks for all your input. truly appreciated. I'm still mulling things over but leaning towards 19's as to not give up the ride quality. I just installed Bilstein Damptronic Coilovers this afternoon and lowered the car by 1.5 inches all the way around. Still rolling on stock 19's. I have to say that the difference is night and day! Wow! I am now able to use the PASM option without the car bouncing up and down wildly. It's just a much better ride overall(both in normal and sport mode). Will give it about a week to settle then will go back for the alignment.

I remember Can's write-up explaining how this is the best thing you can do initially to the car. I would have to agree. Also for some reason, getting rid of most of the wheel-well gap made the stock 19's look bigger. Wheel upgrade is the next step so I would like to make a decision within the next week or so. Will update again very soon. Again, many thanks for everyone's input and opinion.

 

Dave, I just got back from a business trip so I haven't had a chance to take pics, etc. Once I get a moment I'll start up a thread.

I put on a techart1 kit, short shifter and HRE 890Rs with Michelin Pilot Sports...the wheels are flat black with a gloss black lip, black lugs and center caps...all I can say is the car has transformed. I love it.

I took the car for a ride yesterday, in 2 plus years of ownership no one has ever looked twice at the car...well yesterday a guy followed me into a parking lot, waited for me to leave a store so he could ask all about it. He said he never saw one look so great.

I can't say this strongly enough...the 20s are awesome...the car actually feels faster and lighter. I was incredibly worried about it but damn...I would never go back to 19s. Hopefully I can snap some pics shortly...

 

Notwithstanding the physics discussion regarding the carbon/lightweight wheels, there's a lot more to this than rotational inertia. In general, the larger profile of the 18" or 19" versus a 20" allows the tire to absorb a lot of the smaller road inconsistencies that would otherwise have to be transmitted to the suspension. This is a very good thing (within limits - too large a profile and camber/toe/etc start varying too much under cornering to be helpful) because no matter how good the setup, moving all of that suspension unsprung weight compromises tire contact and handling.
Regarding the rotational mass, all things being equal (i.e. for a constant tire and wheel design) the smaller wheel/tire has less weight and rotational inertia. All good things.
So purely for performance, a 19" or preferably an 18" (a size many use for track work) is better. But smaller wheels with higher profiles are out of fashion at the moment (rumor has it that the techs wanted the 997 to ship with 18's) and fashion=marketing=sales. All said though, for street use, it's probably all in the margin.