The topic is weight of wheels and how it relates to performance. I own a 04Z and I've tried really hard to keep the weight down on the Z with the performance up grades. The question is unsprung weight and the rolling mass/inertia/momentum which robs HP. Here's what I'm contemplating, switching my C5Z OEMs for C6Z OEMs. The research that I have done has revealed some flaws in my quest for more rubber under the rear(on a budget).
The facts:
C5Z Alcoas 17x9.5=19lbs
18x10.5=21lbs
C5Z tires Bridgestone Potenza RE760 265/40R17=26lbs(front tires)
Bridgestone Potenza RE760 295/30R18=29lbs(reartires)
Totals=C5Z fronts W&T=45lbs and rears W&T=50lbs per side

Now for the what I was considering
C6Z Speedlines 18x9.5=22lbs
19x12=26lbs
C6Z tires Kumho XS 275/35R18=28lbs(front tires)
Kumho XS 345/30R19=41lbs(rear tires)
Totals=C6Z fronts W&T=50lbs and rear W&T=67lbs per side

So the difference being; Going to C6Zs is an added 5lbs (x2)per side in the front and an added 17lbs in the rear (2x)per side. For a grand total of 44lbs to convert to C6Z OEM Speedlines. That seem ridiculous !!

So 44lbs of rotating mass is equal to 4-6lbs of static weight. We will take the average of 5lbs x the 44lbs gained = 220lbs. WOW. Thats not acceptable.
My car makes about 430 N/A and 600 on spray at the tire, and only weights 2975lbs.
So my question is will I feel this in the seat of my pants ?? The power loss to turn those big lugs is what I'm referring to. And does anyone have experiance with what I'm talking about or input to help ? I take it to the drag strip about once a month and road coure it about twice a year. But I'm not into hopping up the car just to turn around and slow it down with a bad choice of wheels. Not to mention taking a country mile to bring it to a stop.
I'm really looking for hard facts or peronal experiances. For example; if my car runs consistant 10.99's (N/A) could it potentially drop to 11.30's or something like that ?? By just changing the wheel and tire combo. The change is mainly for lack of traction on the street and the 19x12's look sick with the L5 fenders.
Again any input is much appreciated. Thanks..

 

44 lbs of added unsprung weight...you should lose about 3-4 tenths. the rule that i've heard is 10 lbs of unsprung = 1/10 in the quarter 100 lbs of sprung weight = 1/10 in the quarter

 

Use light wheels/tires for racing ... flashy wheels/tires for posing.

 

just so you know...this is easily offset by running a street set of your choice and a set of magnesium wheels or some type of light racing wheels/tires for your track days...even just rears will have you only losing a tenth if you said 5 lbs x 2 on the fronts?

10 lbs = about 1/10 in the quarter. you could probably offset this EASILY with some slicks or something real sticky on your light "race" rear wheels

 

yep, better keep an extra set of wheels for when you want to perform, not pose.

 

Totals=C5Z fronts W&T=45lbs and rears W&T=50lbs per side

95 lbs x2 = 190 lbs x 6.5 lbs rotating wt / 1 lb static wt = 1,235 lbs

Totals=C6Z fronts W&T=50lbs and rear W&T=67lbs per side

117 lbs x 2 = 234 lbs x 6.5 lbs rotating wt / 1 lb static wt 1,527 lbs

1,527 lbs New set
- 1,235 lbs current set

286 lbs difference or 2.86/10s slower in the quarter

just about the same as removing 28 to 29 hp from your engine.

ruff approximations. but close enough

 

This is why I stick with my OEM wheels (front polished 17s are 16 lbs each). In addition, each non-runflat reduced unsprung weight by 6 lbs or so.

 

Performance is always smaller rims and better tires.

 

There are a lot of great points made here. Just to clarify, I have track wheels and tires. This set up is stricly for my street adventures . I'm just not wanting to slow the car down for the street. But needing more traction for the spray !! Hints the 345 with a sticky street tire. And please don't mention DR's because I enjoy the topend handling as well. But thanks again ..

 

Well, a heavier wheel that actually allows you to get traction could still be faster.

But, in general, you are talking first about larger diameter wheels which puts the radius of the mass further out and then adding more mass at the same time which then means more mass at a larger radius.

I put new front rubber on my car and they were something like 4lbs heavier each and I didn't notice any difference with 8lbs more on the wheels. So, I doubt you'd notice that 10lbs added to the front. But the 34lbs on the rear? I'm sure you'd notice that. However, as I first mentioned, if you can't get traction with the rear wheels you have now but you could with the new ones, then the new ones should be better even if they are heavier.

Maybe you really just need to yank those RE760's off and get something that is sticky on the car. I'm not sure what to suggest offhand though. Another option is to not make such an extreme change in wheel size but go enough that you have a better choice of rubber (the Z06 sizes seem so limited) and can find something sticky, like maybe a Nitto or Bridgestone RE050 (not RE050A), however I will say but definately not PS2's.

Peter

 

just wondering?? will the c6 z06 with a 345 rear fit your car???

 

L5's or T2's. Speaking of rear fenders.

 

you will have to run a spacer with the 345 i have 335 on c6 z06 on mine and they rub the wheel tubs. also i think the c6z rims are a little narrow for a 345 tire.

 

Yes, it will require a 3/4 spacer and longer ARP wheel studs. But thats no big deal.