Think one is just one of the newer alloy wheels, the rest are original mag.
Well, the metallurgist/friend got the analysis, and it is not what we expected... The analysis of the chunk of metal from Brian's original, broken, Campagnolo rim that weighs 20.8lbs is... "Aluminum silicon casting". The analysis found "No magnesium in any appreciable level". So, it seems Brian's Bora was delivered or somehow equipped with 5 aluminum Campagnolos without markings or stampings to distinguish them from magnesium rims. - Art
Would Cozza possibly be able to shed any light on a transition away from a magnesium alloy? If true then that would mean that my car probably has the Aluminum rims. One of my wheels developed a porosity or so I was told by Mark Morris Tires in SF. They told me to stop using the rim. Sometimes even respected shops get things wrong. Perhaps it was just a bead sealing issue? The reproduction Miura style rims are aluminum. On a relatively lightweight car you can actually feel the difference in acceleration if you have lightweight rims. I know I did on my GOC. When I had the 3pc rims made so that if I damaged a wheel I could repair it I opted for the more rugged street rims whereas their racing client wanted the performance and were always replacing the rim portions anyway. GD racing is expensive!
Strange that none of us really put under question the aluminium nature of the three "heavy" rims (even if the relative 33% difference in weight was outlined by Art in his #2 post) but actually questioned the origin of the light wheel... 21 lbs for a 7.5 x 15" ally rim is not unusual, and 14 lbs would indeed correspond to the normal weight of a mag wheel of that size. There were reproduction cast aluminium wheels made by Compomotive/Heinbrand, at least for the Campy model of Ghibli/Indy/Khamsin's. Maybe these Bora alloy wheels are not original and were part of a small series made by Compomotive?
Brian has owned that car for quite some time probably at least 20 years maybe longer. I'm sure Walter remembers him from the old Yahoo Maserati discussion group. Were the reproduction wheels around in the late 90's early 2000's?
Here is the analysis.. If it's hard to read, the yellow spikes indicate the elements detected - The tallest spike is Aluminum. - The next tallest is Silica. - There is a tiny bump of Magnesium. - The rest are trace amounts of other elements. - The scanning electron image is of the fracture surface, which our metallurgist says "shows the typical features of an aluminum-silica alloy; ductile areas bounded by plate-like brittle areas indicative of the silica-rich phase". Image Unavailable, Please Login
Probably an eutectic aluminium-silicon alloy, very easy to cast. Not a very strong material such as the forged aviation-grade aluminium alloys. And heavy because you cannot cut corners wrt thicknesses and shapes, contrarily to forged alluminium alloys. Not surprised of the broken wheel, cast aluminium wheels are often used for cheap casting of wheels.
If you've ever seen a naked Miura style wheel the only thing you'd be impressed by is the artistic design. Up close the quality is quite ugly with bent malformed fins and Bondo to repair casting imperfections that weren't structural. Gary Bobileff once told me that for his Miura restorations they used the reproduction aluminum wheels and them had to beat them up a bit to make them appear authentic! LOL. I wonder how those are made? My Bora wheels still look great so I've never stripped them and I hit a pretty tal new paving edge once at 120 mph that made an enormous racket but did absolutely nothing at all to the car. Having more modern and compliant 60 series tires probably helped. That was like hitting four pot holes simultaneously @ 120. The Bora is a strong, tank like car and after that I assumed the wheels were as well.
It is unknown whether we can figure out why this Bora had a complete set of 5 Campagnolos cast in aluminum alloy, with absolutely no markings or indicators that the rims are not magnesium alloy. - Art