Jerry Feather

There is a lot of discussion here recently about the Carrera, Boxster, and Panamera wheels as they might apply to the 928. For the most part the fronts all have 50 or 52mm offsets and when they are 7.5 to 8.5 inches wide that tends to put them both well outside the 65mm offset most desirable for the front of the 928 and, with the 8s, it puts them a bit out side the front wheel arches.

I too have a few sets of the Panamera 8 inch front wheels and have just bought another set of Carrera light weight wheels with the 8 inch fronts and 50mm offset. I have been running Cup wheels on the 87 and they are 7.5 in front with 52mm offset and that is just about the limit of fit inside the non-rolled wheel arches and the limit of the appearance I am willing to go with, not to mention the geometry requirements for 65mm.

I know that negative offset is kind of like catching a fart and painting it green, but I think I have figured out how to do it. I'll be buying some extra parts to deal with and looking into some metal fabrication processes that I think will give rise to just that - - negative spacers for the front. More perhaps as that develops, if at all, and if I don't find myself overthinking it.

icsamerica

So we're going to add something to remove space. Whatever you're smoking... I don't want any.

FredR

All you have to do is work out the square root of minus 50 and you have cracked it!

Ed Scherer

icsamerica

Serously though...before I got my Panamera wheels with 59mm offsets, I considered turning 10mm of the hub face. I dont recall how much material was there but it might be worth looking into.

dr bob

Challenge then is finding negative-clamping lugnutz. Turning the mounting face always sounds like a good idea, but there needs to be enough metal left for the nutz to clamp to the rotor/hat. Further, there needs to be room for the calipers with the wheel mounted.

We need a new billet hub with the mounting face 15mm further in. Then shallower hats on the rotors to keep the brakes lined up correctly. There must be a shallower 911 rotor that would work. There may be the shallower 911 hub bolt-up too, for that matter.

Jerry Feather

Darn, you are pretty quick for a mere User. That is close to about exactly what it will take. However I think it is going to amount to replacing the hub face where the lugs are, at a slightly different location, and either finding a brake rotor with a shallower hat section or taking a section out the the 928 rotor hat.

Or maybe not. I am talking about the hub itself and not the hub face in the wheel.

And then the Doc pretty well nailed it. And there still needs to be enough space between the inside of the wheel and the caliper; and my 87 with cups shows about 5/8 of an inch, so moving the flange of the hub inward about half inch should work.

Good idea to look for another Porsche rotor with the more shallow hat and maybe even a different hub; but I think it might be easier to do the machine work and welding rather than spend the time and money searching through 911 hubs.

dr bob

The factory hubs are quite likely from forgings rather than cast pieces, or are at least pressure-cast with no chance of voids. I'd have to look more carefully at the front hub next time I have pieces off to see how much metal there is to hold the lug bolts if ~10mm is removed. Then still need to find a factory rotor/hat, or get with one of the better brake mfrs to get just the right hat height.

Shirley there's online guidance on the dimensions of the various Porsche hubs and rotors/hats. IIRC the bearings are the same as the other cars from what I remember, but that's a relatively easy fix if they aren't.

Jerry Feather

The Factory hubs look very much like castings. There is not enough material on the mounting flange to turn off much and still have enough left to hold the studs. They look about half inch to 5/8 inch thick.

What I plan to do is turn the entire flange off in such a way that the face, when replaced with half inch aluminum plate, will be a full half inch (about 13mm) inboard from the original face. Then I'll mill a new flange out of 6061 T651 plate and weld it back on. The process is a little complicated, and will involve both my mill and my lathe; and then I'll have the welding done professionally.

As to the rotors, I have in mind something similar. At this point I think I'll simply turn the hat so the the face is free and then turn the half inch out of it then have the face welded back on. I think that will be about as strong as a composite rotor or one with a bolted on aluminum hat.

I'm not sure where or how online to find the kind of dimensions for either the hubs or rotors. As to the rotors my original thought was to simply take one of the rotors to the parts store and see how close I could come to some other make that perhaps requires only re-drilling for the Porsche lug spacing.

hacker-pschorr

I've measured quite a few Porsche (and non Porsche) wheels, and most were around 12-13mm of material between the lug nut and hub.

dr bob

Jerry-- The hubs rotors and wheels are "hub-centric", sliding over the hub so the pieces stay concentric without depending on the bolts on their ball seats.

Look carefully at how you are proposing a welded-on plate. As interesting as it sounds, the lateral forces are tremendous, at the end of of a lever (wheel and tire diameter vs bolt circle) that will multiply the forces applied at you weld. Better IMHO to make a new hub if there isn't another Porsche model with what we need. Kibort had a thread open about his racing brakes supplier and all the hats they make for the various Porsche models. Bet a dime to a donut that the info we need is there.

Jerry Feather

I guess it depends on where on the ball socket for the lug nut you are measuring. From the bottom of the socket to the hub mounting face on all of mine they range from about a quarter inch to a max of about 3/8 inch.

hacker-pschorr

I measured from the widest possible point, since the end result was to determine how much material would be left after machining.

1/4" = 6.35mm
I just grabbed a lug nut, rough measurement of the seat area is 6mm which puts my measurement right in line with your minimum adding the two together.

Bottom line, if someone were to shave off 10mm there isn't a whole lot left.

davek9

My only comment after returning from the 22nd Frenzy and driving hard through the PA mountains and braking HARD at times, is who or how would this be tested and what are liabilities for the manufacture of such a part?
Jerry I love your products/ projects but please be careful with this one.

Dave K

ramcram

Jerry, maybe you can shorten the top wishbone which will bring the wheel in very marginally and move the wheel rotational axis out closer the tyre contact centre?