Wheel Gurus - need help 930 vs WB SC

[mikeatfhc]

I am contemplating purchasing these wheels from another Pelican for my 78 SC wide body.

FS: 17x9.5 and 17x7.5 ROH wheels and RA-1 tires

His car is a 930 - now it's my understanding that the only difference between the SC and the 930 for these years is that the 930 had a 2" wider track in the rear, therefore I am assuming that all's I'd need to do to bolt these up would be to purchase some 2" spacers for the rear to make these work.

Can someone confirm? I do not like the look of these turbo twists!

Thanks.

[KTL]

Those ROH front wheels will fill out a narrowbody car just about perfectly. Therefore you'll likely want to space them out a bit more to improve the look of your widebody. Bit they will fit no problem without any spacers. They'll look a bit tucked under the fenders like a stock 930 does with the 16x7 Fuchs. There's a LOT of room under 930 flares in the front for more wheel. Many people can run 9 inch wheels easily.

The ROH rears have the same offset and a width that is only 1/2 inch wider than the stock 16x9 Fuchs a 930 rides on. So what that means is you should only need the 930 spacers (28mm) and longer wheel studs to reproduce the look of the wheels onto your car. If your car was a SC/Carrera-flared car, you could actually mount the ROH wheels with no spacers and they'd fit very well with only some minor tweaks to the alignment and some ancillary items (trailing arm fasteners & oil line) to get acceptable clearance.

How are the turbo twists currently mounted on your car? Are they OEM Porsche wheels with bolt-on spacers or are they replica wheels with very sizeable hubs? Take a closeup picture of the wheel(s) mounted so we can see how the wheels are connected to the axles.

[mikeatfhc]

Thanks for the info Kevin.

I am pretty sure the wheels are Porsche and not fakes. The car has bolt on spacers all the way around to fit the late offset. I'll try to get out shortly and take a coule of photos for you to be sure. I am really interested in the wheels this gentlemen is selling and would love to make this work. Just as long as the wheels aren't too tucked under then fenders.

[KTL]

Based on what I can see from your picture, you've got stock brakes on the car. Which means the front axle hubs are the standard 911 pieces and not the 930 pieces. Therefore you'll probably have to space out the front a bit to fill out your turbo flares.

SC/Carrera flares are typically described as 9" flares. The 930 flares are called 11" flares. Those 17x9.5 would fit under a 9" flare quite tightly. So with your 11" flares, you should only need the 1 inch spacer to get the wheels spaced out nicely without going to the max. Again, i'd recommend you go with hubcentric spacers and not adapters like you've got now. In order to use slip-on factory 930 spacers, you'll need to drive out the short studs in the axle hub and pull in longer 65mm studs. That's the proper way to space the wheels out- especially if you track the car. Which I assume you will since you're buying wheels with RA-1 tires on them!

[mikeatfhc]

Very, very helpful. I do plan to eventually as I am very close to finalizing my suspension purchases. I recently sold a motorcycle and now the $ is burning a hole in my pocket to buy more pcar parts.

Here are photos of the front and rear hubs with the spacers I am using. Your help is appriciated as I want to do this right, I am going to re-build the entire suspension very, very soon and would like to get this right.

See if these help clarify... FRONT then REAR

[javadog]

For what it's worth, the front hubs of a 930 are wider. In the early 930 a spacer was used (21mm?) and this extra width was incorporated into the late style hubs. An SC is narrower.

In the rear, the control arms are also wider, in addition to the 28mm spacers used. I have calculated the difference and posted it in the past. I don't remember offhand what it was.

JR

[mikeatfhc]

Well I just ran outside and checked the spacers on the car now - I have 1.5" adapter in the front and a 2" in the rear. I thick they are hub-centric as they have the boss that sits in the hubs forcing them to center. Now the question is does that make the front 7+1.5 or 9.5" on a 11 in. flare in the frant and 9.5+2=11.5 in that back?

Or am I missing something terribly obvious?

[KTL]

Spacers set up like that are really not good for high-g cornering. They put so much load on the axle hub due to the long lever arm created by deep wheel hub + spacers. Really takes it's toll on wheel bearings from what I understand. That's one reason why the adaper spacers you have are not typically allowed by groups who organize track events. Usually only slip-on spacers are acceptable and the size is limited. The other downside to adapters is you've got more lug nuts to ensure are tight. You can't inspect/check for tightness the lugs behind the wheels!

The size of your adapters does change the apparent wheel width relative to the car. But the wheel is of course still the same width relative to the tires. If you use the adapters on your car with the ROH wheels, it will certainly push them out as much or more than the wheels you're currently running on.

Your replica (I can tell they're replicas by the deep wheel hubs) turbo twists have an offset of +23mm in the front and +15mm rear. The adapters make them have an effective offset of -15mm in the front and -35.8mm in the rear. Turbo cars do not typically run negative offset wheels. They maintain the offset and instead increase the width, because the big fenders allow for it. I believe the manufacturer stated width of the turbo twist fronts is 7.5 in and the rears are 9 in. The ROH wheels are 7.5 front, +30mm offset and 9.5 rear, +15mm offset.

A comparison of the wheels, assuming width numbers are actual (which they aren't but that's okay), tells me the front ROH wheels will be approximately 1/4 inch further inboard than your turbo twists- IF YOU LEAVE THE ADAPTERS IN PLACE. The rear ROH wheels will move outward an additional 1/4 in.- IF YOU LEAVE THE ADAPTERS IN PLACE.

Bottom line is you must leave the adapters on the car for the ROH wheels to fill the fenders and have the car look good like it does now with the twists. Downside is the adapters are not advisable for track use and you should instead install slip on spacers with longer studs. In front you might even consider getting some 81-89 930 axle hubs to space the wheels more effectively. I've not handled 930 front hubs myself, so I can't give you an exact number as to how much offset is changed with the 930 hubs. But you can see from this classified ad that the tall rear section of the 930 hubs pushes the wheel outboard MUCH further than the 911 axle hub

930 turbo hubs

The rears could get away with the 930 spacers with longer studs. But you'd want to be sure the rear track is wider than the front, depending on what you do up front.

[javadog]

Originally Posted by KTL

I've not handled 930 front hubs myself, so I can't give you an exact number as to how much offset is changed with the 930 hubs.

I'm pretty sure it's 21mm per side.

JR

[Jeff Alton]

21mm

[mikeatfhc]

KTL - your response has been very helpful and enlightening - thanks for schooling me.

I am not tracking the car as yet. My plan is to rebuild the suspension, semi-restore the car for appearance and safety, then do DE and maybe after I learn a bit take it to the track. I plan for this to take a while due to funds. Therefore I could use the adapters I have now for the street and appearance and later as the build progresses and my skills improve - upgrade the spacers. Would you consider the adapters I have now dangerous for the street - or spirited mountain driving?

The owner of the wheel replied that the wheels are set-up for use with lug bolts - my adapters are setup to use lug NUTS. Excuse my ignorance, but could I remove the studs on the adapters and screw-in the lug bolts in their place ala late model cars?

[KTL]

You can certainly use the adapters for street use. It's only when the car is really loaded hard for many cycles (like on the track) will you have problems with bearings and loose lug nuts. It seems that with some adapters or spacers that lug nuts or bolts tend to come loose. I've never had this happen with my car (I use varying size spacers on the rear of my car) but have seen it happen on my friends '95 M3 where we had to keep an eye on the front lug bolt tightness at track events. One time after an event, his wheels starting coming loose on the way home.

I don't think you can use the lug bolts on your adapters, since the studs in the adapters are likely pressed in, not threaded into the adapter. I'm actually surprised to hear the ROH wheels were used with lug bolts. I've yet to see a pre-89 911 with lug bolts and I don't know why one would do that. Lug bolts are typically a pain in the arse to install vs. lug nuts. The wheel is hard to hold in place because you don't have the studs there to hang the wheel on. So i'm not a fan of lug bolts.

Also keep in mind that those ROH wheels probably use a tapered-seat lug nut. The factory Porsche lug nuts are spherical seat lugs. I had a pair of the ROH ZR-6 wheels about three years ago and the shop that sold them to me included the right shape (spherical seat) lug nuts with them.

[mikeatfhc]

Turns out the seller was incorrect - he had to go out to his garage and double check - but the wheels do use lug nuts and he is supplying them with the wheels. We talked last night on the phone, nice guy - so I bit the bullet and agreed to buy them.

Kevin your help here is much appriciated, I've learned a lot. When I get the wheels and mount them I'll snap a photo or two and post the results. Maybe I can elicite your help in the selection of the proper spacers to fill the wheel wells right if everything is off.

Mike

[KTL]

Good news on the lugs issue. Lug bolts are the suck.

Glad to help. I'm betting you'll be pleased with the wheels. You got a very good deal IMO. I was tempted to buy them myself when I first saw the sale ad back in May!

When you get 'em mounted, do take a few pics and the folks around here should be able to point you in the right direction for fitment. Like I said, my approach would be longer studs and slip-on spacers.

Congrats!

[mikeatfhc]

Hey Kevin:

Forgot to follow up with photos of the car with its new choose....

I think the fitmit is great for now... after I finish the suspension, I'll then play with the ride ht and tire sizes. The offset help you gave was very helpful. Too bas she's on jack stands now!!!