19" Z8 'Replica' wheel.

[macfly]

This came up in another thread, and it seems that there is enough interest that we should try to see who would want a 19" lightweight forged version of the Z8 wheel.

The essential criteria for the new rims will be they must look stock, but be much lighter than the stock with a wheel/tire, with a combined weight reduction target of around 60lbs, and also clear the larger Brembo brakes that several of us have.

This wheel may be done as a single or two piece depending on who is our manufacturer, and what makes the most sense to them. I made up this sketch sometime ago as a way to discuss the project with a member who has since dropped out of sight, and it gives everyone something to look at.

[Norcal]

One more category? "on the fence" "perhaps later" "Undecided"

That's how I feel. Since I don't have the big brakes, my immediate need is lessened. And while the lighter weight would be an improvement, for Touring (not track), it may not be that big an issue. The end result would be attractive, but not much visually different from stock. If I am going to invest in custom wheels, I may want something more personalized/unique?
Thus, "on the fence"

[macfly]

Good point, added as requested.

[Z8Mania]

whoa- I wrote a reply and it never took- I just got a blank screen when I hit "post quick reply".. Anyway my thoughts are that I would like to also get sizing that gives us the most choice for tires and also unless someone can convince me otherwise, I prefer single piece wheels vs multi since multi are more prone to losing air.

[2112]

I would be interested if the widths were increased 9-9.5 in front, 10.5-11 in the rear with the backspacing narrower than stock to bring the wheel out to fill the fender to the fullest extent.

BTW aren't many of the top of the line wheels 2 and 3 piece wheels?

[macfly]

If there is enough interest we'll certainly do the widest rim we can, I was thinking of my current widths of 9" & 10", but if 9.5" & 10.5 will fit in the wheel arch then we can do them. We want to make sure the size we pick is one that is widely used so we get the best selection of rubber.

[Z8Mania]

Here is what tire rack says:

http://www.tirerack.com/wheels/tech/techpage.jsp?techid=90

It seems to me that from the standpoint of building a strong, light, and as air leak resistant as possible wheel the desired method is forged monoblock wheel. I believe the OEM Z8 wheels are cast.

[macfly]

I know this may sound like a really dumb thing to ask, but I don't actually know what the difference between forged and cast is!

That point aside there should be no difference between a one and two piece rim so long as the actual rim is a single unit. If the rim is two pieces bolted in the middle (and the spokes make it a three piece set) then I could see the potential for some leakage in the seam.

[jdillane]

Since I use my Z8 exclusively for touring, I like the notion of a lighter wheel that has a stock appearance. Mine is completely stock still as well. I still have the orig run flats and realize that it is time for them to go!

[thegunguy]

Andrew, without going into exhaustive detail, casting is a process where molten material is poured into a mold either using no or low pressure. Forging is a process that forces the material into a die under high pressure in an elastic state, not molten.

The trade offs in the processes is that casting is generally cheaper, but requires more material to be used to equal the strength of a forged process. However, casting can generally produce more complex shapes than forging.

Since I have a "true" performance car, I'm much less concerned about maximizing the capabilities of Z8, befitting to its GT application for me. So, even cast wheels would be acceptable. Certainly, a goal of lessening weight would be nice, but I'd settle for maintaining the weight.

[Grease Monkey]

2 piece wheel designs are no more prone to air leakage than 1 piece designs. Both utilize a solid 1 piece rim. Some 3 piece designs which use an o-ring to seal the 2 rim halves may have a tendency to leak air, but many are welded thereby eliminating this potential leakage point. Forging's biggest benefit is to allow new designs to be created that require less material to achieve the required strength, thereby yielding a lighter weight wheel. A 1 piece forged reproduction of the OE Z8 wheel probably won't weigh a whole lot less because the design has already been established. Some weight could be saved by increasing the hollowing out of the spokes and thinning the rim thickness, so perhaps a 19" version could be manufactured that was similar in weight to the 18" OE cast aluminum wheels, but it remains to be seen whether the Z8 wheel design can be forged or if it must be cast due to the shapes involved. A 2 piece approach would allow the rim to be made from a magnesium alloy, which would make the wheel significantly lighter in the critical outer circumference area, and then the center section could be cast from aluminum. Or the whole wheel could be made from a magnesium alloy which would produce the lightest wheel possible (carbon-fiber not included) but raise the expense considerably. While it is tempting to try to fit larger wheels and tires in the rear to fill up the wheel wells, this approach will alter the car's performance in ways that may not be beneficial. It will increase the spread of tire widths front to rear which will increase the car's tendency towards understeer and increase unsprung weight, particularly in the critical outer perimeter area, which will require more horsepower to accelerate and more braking power to slow the car. I think all of the aesthetic concerns in the rear can be addressed by judicious offset choice. Up front, the Z8's suspension design severely limits what can be used unless you are willing to increase negative camber substantially, so going much wider may not be prudent. I would suggest 9" front and 10" rear since that modest increase will allow a wider choice of tires for the car without complicating their fitment.

[Z8Mania]

Good points GM.

[macfly]

I spoke to a manufacturer here in the US (Alcoa in Detroit) and in the EU (BBS) and the end result of my learning was making the wheels is simple, but getting them DoT approved and tested is not - it is a very expensive and difficult process. If I commissioned the wheels without doing it, and one of you became involved in a subsequent accident with the wheels on the car, and they could be in anyway found to be faulty, at fault, in question etc, legally the buck would stop here, so I pulled the plug on this one for good and always.

Anyone else wants to take the ball and run with it please do!! :thumbsup:

[thegunguy]

Makes sense. I'm so pleased with my new wheels, my interest on these has plummeted.

[macfly]

I'm so pleased with my new wheels, my interest on these has plummeted.
Me too, despite the flack mine seem to be attracting!!!

[Norcal]

Andrew, have you figured out why you were having clearance issues with your new wheels?

[macfly]

Yes, the wider footprint of the tire, it was rubbing on a bit of inner fender plastic. My solution is try about 1/4 - 1/2º more negative all round, and I'll also follow GM's advice and put a little spacer on the front to widen the track. When all that is done I plan to take it to WSIR (with the Jack pack) for a final proof of set up, and also a solo photo day since my poor car has been completely neglected by my camera all year, and there are no great shots of it with it's lovely new rims!

[thegunguy]

What's the date at WSIR?

[macfly]

No date as yet, gotta find the right shop to do my new alignment down here first, and then see what day the Jack pack will be at WSIR. I'll email Jack today and see if he has a day in mind.

[Z8doc]

Me too, despite the flack mine seem to be attracting!!!

Not sure about that? Just comparing old vs new?

[macfly]

I am currently in talks with HRE who say they might be able to make replica rims for us in wider, lighter 19" monoblocs, and get the TUV approved for Europe.

Let me know your thoughts.

[Z8Mania]

Andrew, depending on the specs etc, I could be very interested. I'd love to know details as they are available.

[Z8doc]

Ditto .... Interested too as we have discussed this before. Keep me posted!

[thegunguy]

I noticed the poll is from the original post from "way back when". I think this is a great project, but I'm no longer interested. Other than weight, I love the M166 wheel that I'm running. Visually, it's perfect to me.

[jwgerritsen]

I am interested in the 19inch, pls let me know if you make progress

Thank you