Simply from a qualitative point of view....

Rods in tension are very strong. Any lateral forces on the studs (in or out of the face of the wheel, parallel to the studs) for either configuration should be handled with ease. Even a twisting of the wheel (say in the camber like axis form rubbing an apex curb or the toe like axis from a hard turn in) would not be able to bring these studs out of tension.

However, any longitudinal or vertical forces will be attempting to shear the studs. This is not good for your long stud and spacer configuration. The problem can be modeled with a stud represented as a simple beam. Where the stud is attached to the hub, it has a solid connection. Beyond that is the beam part. In your case, a load is applied by the wheel, at approximately one inch for the spacer plus half the thickness of the face of the wheel (making the simplification of applying all of the wheel's forces at that point). This creates a long moment arm. Since the spacer is just a hole, it doesn't do a whole lot to oppose this bending moment.

With the bolt on spacer, however, the total bending moment is decreased. Transfering the load form the wheel to the spacer, the force from the wheel only acts over a moment arm of about half the thickness of the wheel face since the studs bolt directly into the spacer. On the other side, when the force is transmitted from the spacer to the hub, the moment arm only acts over half the distance of the spacer's bolt holes. The missing step is transfering the moment from one side of the spacer to the other. As you might imagine, a 1" long moment arm over a 4" diamter piece of metal doesn't see a whole lot of bending, so it might as well be ignored. This makes the effective moment arm for this configuration smaller. How much smaller? Judging by the pictures, about half an inch. You'd have to consider the thickness of your wheel face to convert that into a percentage, but it's not insignificant.

Mike brings up a valid point that a cracked spacer with extended studs could be less dangerous than a cracked bolt on spacer, but I'm not sure what would crack it to begin with.

Either way, I would imagine both products have been designed to endure. I wouldn't think one would be the obviously better choice from a safety stand point.

 

[QUOTE=FormulaRedline,Nov 3 2006, 12:08 PM] However, any longitudinal or vertical forces will be attempting to shear the studs.

 

Yes, this is certainly true.

 

Indeed it does.

But adding another pass through spacer plus an inch of stud is a completely different story. If you forget that part in your equations, you're missing the most important change.

 

Not really, as long as the stud remains under enough tension.

 

So which is the safer setup?
1. One inch spacer with extended wheel studs
2. One inch spacer bolted to hub, with separate spacer studs used to mount wheel

Since I'll be running a LOT of tire and those tires will be race slicks not DOT R ... I'd like the strongest, most reliable setup.

 

One might not be as risky than the other, but in your situation I not consider either one as being safe. The part I really don't like is you're trying to fit the maximum amount of tire and grip on your car and possibly compromising the mounting system to do so.

There are guys breaking rear hubs with wide slicks. I would not want to risk that kind of load while using wheel spacers on top.

Having said that, if it were my car and I were forced to use one or the other, number 2 would be my first choice. Just make damn sure you are getting a quality piece and keep a close eye on it.

 

The walkway failure was due to the nuts supporting the 4th floor having to also carry the load of the 2nd. The way it was originally designed the nut would only carry the load of the 4th floor but the change doubled the load on the nut.

With the spacers that's not the case. The nut holding the spacer to the hub carries the load of the wheel and the spacer. It would be the same if the hub connected to the wheel and the spacer connected a second wheel. In that case the studs of the spacer would carry the load of one wheel and the studs of the hub would carry the load of both wheels.

 

Sounds like too many Molson's.

 

Huh?

I think I need more to drink before I can understand that one.

I'm not sure what to believe on the wheel setup / spacer. John at CCW is adamant that their's no issue as he was when he recommended this approach.