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Scored some 996 GT3cup centerlock E29 wheels. I have always liked the solid spoke wheels over the scalloped spoke BBS motorsport wheels so after a bit of research I caved and bought some. And seeing that from the backside the E29 wheels were identical to the other BBS motorsport 5-lug wheels except that the 5-lug holes were drilled all the way through and the frontside was milled for the lug and socket recesses, I had no issues with converting these to 5-lug. Especially seeing Porsche motorsport was offering this conversion.
So with my machining knowledge, some Porsche race engineer consulting and a drawing from BBS on the lug hole dimensions I went at it. To bore the recess for the socket is easy. But you have to start by locating the 5-lug holes and through drill. It is important to drill straight and center the through holes on the existing and correct drive pin holes. Once drilled through, you use 2 different piloted counterbores which ensure accurate boring of the socket recess. The lug seat is 14mm radius. So this was custom ground piloted counterbore. Here you can see the through drill and the socket counterbore. Following the BBS dimensions ensure you are not weakening the wheel and allow enough material for the lugs to adequately hold. Also that you don’t cut through into the other drive pin recesses near by. And with our wheels being hub centric you really have to hack up this process to ruin a wheel or modify and make a unsafe wheel. Anyways, once I have my special ground counterbore for the lug recess then that will be complete and the wheels will get painted BBS gold. Then clear coated.
I wouldn’t suggest this process to anyone unless you have the data, correct tools and machining experience. Also, the E88 wheels are available in the 5-lug configuration and are lighter than the E29 wheels. So unless you are like me and enjoy a good engineering and machining project, this isn’t for you. Also, I really dig the solid spokes over the scalloped spokes personally.
Looking good, but does the wheel lost stability cause of lost material? I do hope not...
No. As the post says, this conversion has been done for years and run in the Porsche Cup grand am cars with much more abuse and forces than street driving. And as I said I got schematics of the BBS 5 lug wheels with dimension to go off of. If this type of work scares people and they are not willing to do the research to mitigate issues, they don’t belong doing this type of work.
Whats the point doing this? Are they light and/or cheaper than E88s?
You really should read my post. It explains this. As far as price, for what I have into this, used E88s would be the same price. And as I mentioned I do not like the scalloped spokes on the E88s nor the rim halves mounting behind the center.
I have a set of Porsche motorsport converted CL wheels - but mine are the E88's = I imagine yours are easier to keep clean
I can only imagine the difficulties getting into the scalloped areas, but they are lighter wheels and anything in those spokes are probably more difficult to see.
Got it. Great work good job. I want a set too
