Rennlist - Porsche Discussion Forums - BBS E29 5-lug conversion

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BBS E29 5-lug conversion

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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. https://cimg2.ibsrv.net/gimg/rennlis...7031bc029.jpeg
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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.

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.

And I'd just talked myself out of a Bridgeport. Nice work.

More picture updates

Good work! They look outstanding. I also like them without the scallops. I wish I had a set of those. Keep the pics coming. Best Josh

Quote:

Originally Posted by gt2-josh

Good work! They look outstanding. I also like them without the scallops. I wish I had a set of those. Keep the pics coming. Best Josh

Thanks Josh! They pop up from time to time. Just look for Porsche 996 cup wheels. The are the aluminum E29s, not the magnesium E28s.

Thanks Kraut. I would LOVE to build a set around these centers. Unfortunately I lack the wrenching skill. You are building my dream wheels. Best Josh

Nice work!

I think a lot of us feel the same way about the scallops. What is the easiest way to tell which wheels are alloy versus magnesium? I've tried to do some research but haven't had much luck.
Any help with that question would be much appreciated!! Thanks!

Regards,

.

Kraut, If you have an extra set I'm a ready buyer!! Please keep us updated with pics. Thanks again. Josh

Quote:

Originally Posted by Cemoto

For the 996cup magnesium wheels most were easy to tell because they were factory 5-lug and also the centers mount outside of the the wheel halves. Like these:

Amazing work!! - How do you know which blind holes to drill? Are there 5 specific? Or as the PCD is 130 can you start with any hole and go from there?

How did you know how far to count bore the front face?

I have a set of 996 cup magnesium BBS wheels - they don't have any provisions for the 5 lug pattern - not saying that they couldn't be drilled...

Quote:

Originally Posted by Evil Bunny

I based this on the E88 wheel lug depths, which are deeper than the lug depths on the E28 magnesium wheels. I then bored so that had more material for safety margin. As for the drive pin holes, they are 130mm same as lugs. You can pick from 3 sets of possible 5x130 holes. I chose the ones that line up with the spokes.

Your rims turned out very nice! I actually have a set of these AL centers AND 1.5 sets of the Magnesium centers - none look very much like these :-)

Ray

Thanks again for the info, its the depth of the counter bore I am trying to figure out.- It looks to me like the counter bore runs down flush to the face of the wheel, and from the face down the R14 seat is machined - Would you say this is correct?

Also, I can see the depth of the counter bore being critical if your using wheel bolts, as you need to ensure enough of the bolts thread passes through the wheel and into the hub, however if your running wheel studs, could the depth of the counter bore be calculated by ensuring that there is enough depth that when the stud to pass through your able to fully thread the nut on before it makes contact with the wheel? - With this in mind you may also be able to count bore less and leave more material on the wheel.

I welcome your thoughts, I am currently looking at drilling a set of E28's but there is not much information available. - All help appreciated!!

Quote:

Originally Posted by Evil Bunny

For the E28s, contact BBS and ask for a drawing that shows lug depth of wheel center PN 0228291. This is a 5-lug E28 factory 996 cup center. If you you have lug depth, you can measure and come up with what the counterbore depth is by measuring the entire wheel center hub depth. Keep in mind the face of the E29 wheel center steps thinner from in the lug area than the CL washer mating face, so measure that. The E28 should be flush with the CL washer mating face. Lug depth is what determines how much you counterbore. You will need to take into account conical seat depth. So ideally you would take lug depth from the bottom of the conical/spherical bottom and add the lug seat depth. That would tell you how far to counterbore. You want enough lug seat cup to seat the entire lug seat face. Does this help?

Might I add that if you talk to BBS and tell them you are altering wheels, they are likely to not help. So, make sure you ask wisely.