Cloud968
Cloud968 New Reader
8/8/17 9:57 p.m.

Hello - this is my first post, other than my intro. I have a track-prepped 1992 Porsche 968 with 2.25" id coilovers all around (torsion bars deleted), and am looking to improve the car's grip by fitting wheels that are wider than my current 17 x 9's. An experienced racer on one of the Porsche forums told me he has fit wheels as wide as 10.5" on the front. I think this is possible, but it will be a tight fit. My major obstacle is that Porsche uses a unique-to-Porsche 5 x 130 mm bolt pattern, and the front hubs stick out far enough to require an offset that's larger than typical. So, off-the-shelf wheels are off the table. Several people have advised me to look into 3-piece wheels, which I should theoretically be able to assemble such that they clear my springs and fender. But after literally hours of searching, I'm not finding much in the way of guidance as to how to convert my fitment needs to the width of the inner barrel and outer lip, and the wheel center design, of a custom-assembled 3-piece wheel. I found a calculator that tells you the sizes of the new pieces that would be needed to convert from an existing 3-piece wheel to one that ends up at a different desired width, but so far nothing on how to put together a 3-piece wheel that will fit my particular application. Bob Woodman tires seems to have a good selection of 3-piece wheel components, but their site doesn't really explain how to go about selecting the sizes of the components. I've emailed them, but haven't heard back.

So, if someone has some direct experience with sizing and compiling the components of a set of 3-piece wheels to fit a particular, custom application, or knows of a good resource that could guide me through the process, I would really appreciate it. Thanks in advance, and I'm looking forward to being an active participant on this forum.

Andy N Austin, TX

chandlerGTi
chandlerGTi PowerDork
8/9/17 8:10 a.m.

There are a lot of variables, I built the wheels on my daily to fit the wheel wells perfectly and it was trial and error.

I think you should start with the centers you want to run, mount them and start taking measurements. You will need the measurement from the faces bolt ring in and out then convert it to however whomever you are buying the wheel halves from is measuring. Usually a 6" lip is really 6.5", but I've seen others include the full width.

z31maniac
z31maniac MegaDork
8/9/17 9:04 a.m.

Before bothering with the very large expense of building 3 piece race wheels (which tend to be heavy for their size unless you're spending huge $$$$$)

I'd call someone like Forgeline or Rotiform to see what they could make you.

What offset are you current wheels? How much brake clearance do you need? ETc.

dean1484
dean1484 MegaDork
8/9/17 1:30 p.m.

I have a set of dp's that are three piece. For my 924s. I found them to be HEAVY and actually liked the set of stock rims off a 928 better due to them being much lighter. The car felt soggy with the dp rims on turn in where as on the 928 rims it was crisp. Tire type was the same.

dean1484
dean1484 MegaDork
8/9/17 1:31 p.m.

Mine look like this.

GameboyRMH
GameboyRMH MegaDork
8/9/17 1:35 p.m.
z31maniac wrote: Before bothering with the very large expense of building 3 piece race wheels (which tend to be heavy for their size unless you're spending huge $$$$$) I'd call someone like Forgeline or Rotiform to see what they could make you. What offset are you current wheels? How much brake clearance do you need? ETc.

Or maybe even before that, consider a hub conversion to a more common bolt pattern? It'll save on wheels but the brake discs will have to be redrilled.

Stefan
Stefan MegaDork
8/9/17 2:17 p.m.

In reply to GameboyRMH:

Finding wheels for that pattern isn't that hard. Its affording them as they are just simply expensive.

Changing the pattern is a bit extreme, but not impossible. There was a person working on building new front hubs for his 924 to use 4x100 bolt pattern and it looked like a fairly simple CNC job. The 944 hub isn't much different. Better if you can design the hubs for the rotors instead of the other way around.

The rear is trickier due to the required splines for the stub axles, but since many are used on Super Beetles, you might find some parts from some of the disc brake conversion sets sold by companies like CIP1.com that have bolt patterns other than 5x130mm. Worst case, one might be able to redrill the rear hubs, but finding rotors to fit and leverage the parking brake might be a tall order.

I'd look at Diamond and Revolution for custom wheels before I went with a 3-piece wheel.

You can always add a small spacer to make slight adjustments, especially to compensate for manufacturing and adjustment tolerances.

One thing to note with the 924/944/968 is that Porsche paid a lot of attention to the scrub radius on the strut based front suspension used on those cars. Basically if you draw a line from the center of the strut down to the ground, it lands in the center of the contact patch.

With wheels larger than 16" in diameter, they recommend more static caster to compensate for the extra load generated.

chandlerGTi
chandlerGTi PowerDork
8/9/17 3:18 p.m.
dean1484 wrote: Mine look like this.

I have a set of DP Enduros as well, from an NSX. Great wheels made by Works.

Cloud968
Cloud968 New Reader
8/9/17 6:40 p.m.

Thanks for all the feedback. After thinking about it a little more, I think I have a general idea of how I would go about sizing the components for a 3-piece wheel, if I end up going that route. I also got a response back from Bob Woodman Tires, who stocks new and used BBS components. I don't yet know the price for a complete wheel, as I don't know whether used components are available in the sizes I need, but they have to be a lot less than Forgeline, which runs in the neighborhood of $1400/wheel! No can do. From what I've gathered, BBS 3-piece wheels are fairly light (my current 17 x 9" are 21.0 lbs), but I could be mistaken, as weight estimates can be wildly inaccurate, usually on the low side. As far as re-sizing the hubs, that sounds like a bit more of a project than I'm interesting in taking on at the moment.

chandlerGTi
chandlerGTi PowerDork
8/9/17 7:33 p.m.

For new custom stuff that $1400 a wheel isn't bad, my one piece forgelines were 950 each in the late 90's early 2000's. Did you try the forums on pelican? Wheels for sale all the time for decent prices.

z31maniac
z31maniac MegaDork
8/9/17 8:02 p.m.
Cloud968 wrote: Thanks for all the feedback. After thinking about it a little more, I think I have a general idea of how I would go about sizing the components for a 3-piece wheel, if I end up going that route. I also got a response back from Bob Woodman Tires, who stocks new and used BBS components. I don't yet know the price for a complete wheel, as I don't know whether used components are available in the sizes I need, but they have to be a lot less than Forgeline, which runs in the neighborhood of $1400/wheel! No can do. From what I've gathered, BBS 3-piece wheels are fairly light (my current 17 x 9" are 21.0 lbs), but I could be mistaken, as weight estimates can be wildly inaccurate, usually on the low side. As far as re-sizing the hubs, that sounds like a bit more of a project than I'm interesting in taking on at the moment.

18x9.5 RPF1s are 3.4lbs lighter. That's heavy.

TWS wheels are even lighter than RPF1s.

3 piece wheels are heavy.

codrus
codrus UltraDork
8/9/17 11:46 p.m.
z31maniac wrote:
Cloud968 wrote: (my current 17 x 9" are 21.0 lbs),
18x9.5 RPF1s are 3.4lbs lighter. That's heavy. TWS wheels are even lighter than RPF1s. 3 piece wheels are heavy.

Yeah, the 17x9s that I put on my FD are 17.4 pounds.

z31maniac
z31maniac MegaDork
8/9/17 11:53 p.m.

Crap, maybe I meant 2.4, still significant for the size difference.

Forgive me, I've been celebrating my offer being accepted to buy a house :)

pimpm3
pimpm3 SuperDork
8/10/17 6:43 a.m.

Check with CCW here in Florida. They can make you whatever size and offset you want.

Andrew
Andrew New Reader
8/10/17 8:10 p.m.

Sigh. I wish RPF1's were available in my bolt pattern. And offset. And width. No, the only way to get the size I want is to go the custom route, whether monoblock or 3-piece. I emailed CCW, but got no response. Same with Fikse - pretty disappointing, actually. I like what I see on Bob Woodman's site, since they deal in a lot of used components, so hopefully if I'm patient enough, I will be able to piece together something that isn't going to break the bank. This is just a car I take to track sessions - nothing competitive - so spending upwards of six grand on a set of wheels just doesn't make sense to me.

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