cruisemon

99C5Vert gets it.

Thank yuh vurry much.

Charlie

Allthrottleandsomebottle

This one has come many times over the years............on my 97'
I dynoed on the same dyno, different days but the DA was the same..........from a 345/35/18 on a 18 x 12 HRE 545 @64 lbs ea to a 345/30/18 bfg dr on the same wheel....@57lbs. HP was less than 5 difference. As for rotating..........
FWIW,
I lost 84 lbs of wheel/tire combo weight going to a CCW drag pack.............and went from a 10.97 to a 10.87. 60' & DA almost identical
I have done tests on that.........

My street setup:
HRE 18 x 9.5 545 w/ clear center +58mm w/ 275/35/18 BFG KDWs 52 lbs ea.
HRE 18 x 12 545 w/ clear center +74mm w/ 345/30/18 BFG DRs 57lbs ea.

10.97@122.45, 1.528 60', DA -760

My CCW drag pack:
CCW drag pack rear 16 x 10 classic full polished with well worn MT ET Street 26 x 11.50 x 16 (1/32” tread) with center caps 34 lbs ea.

CCW drag pack front 16 x 5 classic full polished with like new Firestone deluxe champion 5.00/5.25-16 (10/32” tread) with center caps 33 lbs ea.
10.87@125.42, 1.538 60', DA -790


And with 345s in the back and CCW skinnies in the front...

10.93@123.93, 1.498 60', DA +300


So loosing 84 lbs of rotating mass gets ya about 1/10th.
Results may vary

cruisemon

Back up the thread I mentioned that people will sometimes spend a lot of money to pick up a tenth. I had a '56 with the 2 X 4 245 hp engine that I used to campaign. I told my wife to get her fat @$$ out of my car and picked up FOUR tenths. It cost me a house, alimony and child support, but mommy did the car ride better.

Charlie

AU N EGL

Interesting.

Lots and lots of verables as other have mentioned.

I picked up about 5 hp going from a heavier 51 lbs each rear wheels to my race wheels at 39 lbs each

Wndotintman

[loosing 84 lbs of rotating mass gets ya about 1/10th.
Results may vary [/QUOTE]


Sorry, I really didnt mean for this thread to get that in depth....

So I really shouldnt worry about adding 16 lbs of rotating mass with a
CCW 19" set up.

Allthrottleandsomebottle

I wouldn't...enjoy it, thats all that matters.....just add some more ponies under the hood
Depth, no worries........all cut and paste from years ago

AU N EGL

Get the wheels and enjoy the factor.

Wndotintman

Now another thought. 18s or 19s. I can save around 6 lbs going 18s over the 19s. Street use only. Any thoughts?

blk_vet

Nice

AU N EGL

There are also greater tire selection by using 18" all around. Many ppl use 18" on all four corners.

My street wheels (CCW Classic Street) are 18x10f 18x275/35 and 18x12r 18x335/30 Mich PS

STLKillerC5

Get the 18/19 combo. Looks sweet and who cares about a couple of Hp or 1/10th of a second!! Send out pics when you get them installed. I'm looking at wheels and I think I'm gonna do the 19/20 combo. I've seen some pics with Iforged sets and they look sweet.

McQuickster

I know that this thread finally got back on track, but.......
Even if the car is not accelerating, the wheels are accelerating inward towards the wheel bearings whenever they spin. This is centrifugal acceleration, and it takes power to contniue to spin even at a constant speed. If you put a 5 lb weight on a 1 ft cord and the same weight on a 2 ft cord, you will see that it takes a lot more power to swing the 2 ft cord at the same RPM as the 1 ft cord. So the 2 main things to consider (probably leaving out 7 others) are the amount of rotating mass and the distance of the mass from the center. So the actual design of the wheel makes all of the difference. You could have a 17 inch, 20 lb wheel that has a center made of titanium, and a perimeter made of lead that contains most of the mass far away from the center. You could also have an 18 inch, 24 lb wheel that has a lead center, and a titanium perimeter that has most of the mass close to center. The larger, heavier wheel could possibly have less inertia in this extreme case, and require less power to keep spinning. But in most cases, a larger heavier wheel has similar mass distribution to a smaller lighter wheel, and therefore the larger one will require more power to get up to speed AND continue to spin. I hope this makes sense and that I am not missing key points. Oh yeah, I think most people would agree that a larger diameter wheel also reduces the torque ratio. Let me know if I am way off on this one.
Josh

99C5Vert

That's wrong... think about newton's first law... body in motion stays in motion. If you had a wheel on a frictionless bearing, in vacuum, and it was spinning at 200 rpm, it would stay spinning at that speed forever... no power required. The only thing that would slow it down is that there is really no such thing as a perfectly frictionless environment. It doesn't matter if that wheel weighs 2 lbs or 2 tons.

Half-Life

itchynackers

The only real way to measure the force it takes to rotate a wheel is this...

Mount the wheel & tire on some sort of free-spinning axle. Wrap a cord around the tire (a few times) with a weight (say 1 kg) on the end. Measure the time it takes the weight to fall from its height to the floor. The quicker time will be the quickest wheel & tire combo at the track (assuming no wheel spin).

Like this...

99C5Vert

That would measure how the wheel accelerates (picks up speed). if the car is running at exactly 6000 RPM in 4th gear, the wheels won't be changing speed.

AbsolutHank

Look...I didn't major in physics, but I can tell you there was a noticable SOTP loss in power when I went from my stock wagon wheels to 18/19 Z07 wheels. To the original poster...I don't care if physics doesn't prove it, it was definetely there and enough to convince me to get some lighter wheels

obxfunn

I was in this same spot a few days ago. I want new wheels on my Z06 but was worried about weight issues. I finally went with CCW 505A's 18x10 and 18x11.5.

What made me stop worrying is that I also ordered the parts to forge my motor and jump the boost from 8# to 14# plus add a new cam. Should take me from 580rwhp to 700ishrwhp. I figured the extra weight isn't going to matter much.

Wndotintman

I am sure you did notice a big difference in those wheels. I really like the looks of the Z07 wheels but they are heavy. I was interested in them until I found out how much they weigh.

99C5Vert

no argument that there is an acceleration difference. original question was if there was a dyno # difference.