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PostPosted: Sun Nov 12, 2017 8:58 am 
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Navy Lifer wrote:
kevink wrote:
Maxspeed96ct wrote:
Some call it 5x120, 5x120.65 or 5x4.75, depends on the manufacture. Its the same

I have heard this, too. The common argument is that they are all 4.750" (which is exactly the same as 120.65mm) and if a wheel or car is said to have a 120mm bolt pattern, the manufacturer is just stating the size as 120mm instead of 120.65mm. I don't think this has ever been proven. I never really cared or thought of a way to actually put this to the test... until now. I drilled two bolt patterns in a piece of 0.250" thick aluminum on my mill which does bolt circles. I made one pattern 5x4.750" and the other one 5x120mm. My studs measured 0.545", so bored all the holes to exactly 0.546" with a boring bar. The initial hole was made with a 0.500" end mill, so there was no chance of a twist drill walking. The bolt circles are perfect. Well... the 120mm bolt pattern fit over my studs perfectly and tightly. The 4.750" bolt pattern only fit over the portion of the studs that is not threaded and a smaller diameter than the threaded portion. It was clear that each stud was not centered in the 4.750" pattern's holes. You can sort of make this out in the photo. That being said, I still have yet to hear of a failure by using 5x4.750 wheels on a 120mm car. The difference is pretty small (about 0.013" per stud).

Nice demo - the pattern measures out to 4.75 vs 4.72, admittedly not very much, but clearly different enough to indicate that a wheel for one pattern does not center up as intended on the other pattern.

My issue is the act of torquing the wheel nuts (spec to 140 lb/ft) will result in very heavy contact on the most-inboard point (radially) on a Corvette wheel, effectively "pinching" the wheel and heavily loading a very small area, and leave the rest of the seat taper less loaded. It will also place a bending load on the wheel studs as the wheel nuts are drawn to full torque.

Try putting some Prussian Blue or Dykem on the tapered wheel seats of a Corvette wheel on 120mm pattern and just snug up the lug nuts, then check the contact on the seats. Then do the same with the correct 120mm wheel.



doing a dykem/prussian test would be good to see

kevink wrote:


bill did you see these ?


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PostPosted: Sun Nov 12, 2017 1:35 pm 
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Yes--I did look at these via the link - not much info about the design, and with the precaution about not using an impact tool, I would question their durability in regular use...and then there would be a concern about corrosion over time with a daily-driven vehicle situation, especially in northern-tier states. I can just see a potential for unanticipated and/or bad things happening.

I'd like to see just how these parts are made to understand more clearly how they work. before making any further assumptions. If they function as described, it would be better than just slapping on Corvette wheels to a 120mm hub and using the production lug nuts, but whether they will withstand shock loads of a drag racing launch, and whether loss of thread contact (below minimum of 7.5 turns for 14mm) is part of the "solution" to have a floating lug seat, which I believe is the only way this part could do what it claims, are my concerns, without knowing more about them.

To me, "wobble nuts" are no substitute for doing it right. The difference in the 120 & 120.65 bolt circle can be easily fixed by a competent machine shop that does pattern correction--essentially changing a Corvette wheel to 120mm bolt circle--and everything is just fine, as long as the hub centering is also addressed.

With no centering ring, a 120.65 wheel can easily be mounted off-center--put on the first lug nut and tighten it (so that lug contacts wheel seat evenly), and the remaining 4 fastener joints are all under even greater stress. It can and will create vibration, at the very least. Anyone doing this with a set of slicks may not notice it as readily, depending on what rear tire pressure is being used, as sidewall flex would tend to mask the off-center wheel mounting, even though there may be no detectable symptoms--but the wheel can still have up to a 0.03" "orbit" in this situation, certainly not right, and not good long-term.

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PostPosted: Sun Nov 12, 2017 4:19 pm 
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I wanted to add some background to the full discussion on wheel swaps using wheels with different stud patterns and hub center bore/register dimensions.

Some years back I discovered that there was a rotor that was common to 2 distinctly different GM platforms--one RWD and the other FWD. After understanding the how & why, it was easy to accept, but it was quite confusing initially.

Considering that brake rotors are not centered by the wheel studs, this then raises the question of how it could be OK to have wheels centered by the studs, when we look at the differences in OE wheel center bores between Corvette and Zeta cars (70.3 - 70.5 vs 67.4). Production "fit" is not as tight as is possible to achieve with aftermarket centering rings, and most OE tapered-seat wheels are considered to be a combination of hub-centric (to roughly center wheels with studs) and lug-centric (to bring the wheel into a concentric condition) on the hub.

Here's the rotor info:

Centric front rotor PN 12562055 - http://www.rockauto.com/en/moreinfo.php ... 76&jsn=490

Buyer's Guide info:
CHEVROLET CAMARO 1998-2002 - 120.65mm stud pattern (F-body)
CHEVROLET IMPALA 2000-2005 - 115mm stud pattern (W platform)

2.78" advertised rotor ID to center rotor on hub = 70.6mm, which is larger than the 4.75" wheel/hub size. This is common on both hubs:

Hub info for Camaro & Impala:
Camaro - http://www.rockauto.com/en/moreinfo.php ... 76&jsn=516
wheel pilot: 2.76 = 70.1mm

Impala - http://www.rockauto.com/en/moreinfo.php ... 95&jsn=632
wheel pilot: 70.1mm

Parts commonality (providing service parts inventory reduction) was the clear goal - so a common hub register dimension was essential. The accommodation of the different wheel stud patterns was achieved by over-sizing the 5 holes in the rotor to allow it to work with both stud patterns, both vehicles using M12x1.5 studs.

So, what does this have to do with wheel stud patterns? It's the reality that just as a rotor is centered on/by the hub, so that the rotor does not "orbit", causing an imbalance/vibration condition, the wheel relies on this same centering action, to minimize vibration. Mounting wheels that do not have the same bolt circle, let alone the same center bore, is not consistent with the efforts made by the OEM (GM in this case) to provide this centering feature.

Since the (2002) FWD Impala has a matching center bore to the (2002) RWD Camaro, would it be OK to use Impala wheels on the Camaro, considering the rotor is common? Well, with 115mm bolt circle (BC) on the FWD platform, and 120.65mm BC on the Camaro, the answer is no, even though they're hub-centric. The same logic applies with the mismatch of BC between Corvette wheels and Zeta platform--AND they are NOT hub-centric!

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PostPosted: Sun Nov 12, 2017 4:45 pm 
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s/c'd cav wrote:
doing a dykem/prussian test would be good to see

kevink wrote:


bill did you see these ?


I have the Dykem, but no 4.750 wheels! That link was just the first example I found. There seems to be a lot of different designs out there.


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PostPosted: Sun Nov 12, 2017 5:00 pm 
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so here's a link to a site where the design of the seat is more clearly shown--still curious how the moving seat can be held to a specific torque over time, and whether corrosion can become a problem. It does not appear to compromise the needed thread engagement as I had mentioned previously. These happen to be M12, but I'll assume there's a M14 version available of the same or similar configuration.

https://www.urotuning.com/PCD-Variation ... 12x1.5.htm

This appears to be a pretty good link that will take this topic through the experience of others to help everyone see - including some good illustrations - what I'm saying about the BC (PCD) mismatch of Corvette wheels on PPV/Zeta vehicles.

http://www.team-bhp.com/forum/tyre-allo ... ality.html

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PostPosted: Sun Nov 12, 2017 8:40 pm 
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Navy Lifer wrote:
This appears to be a pretty good link that will take this topic through the experience of others to help everyone see - including some good illustrations - what I'm saying about the BC (PCD) mismatch of Corvette wheels on PPV/Zeta vehicles.

http://www.team-bhp.com/forum/tyre-allo ... ality.html


A lot of what's in that post seems pretty obvious to me, but "Patchboy", whoever that is, seriously contradicted himself:

"Nearly all OEM Wheels are designed to be hub-centric. The auto maker designs an OEM wheel to fit on a certain car or range of cars. The center bore of the wheel is sized to fit perfectly onto the axle of that car. This is a hub-centric connection, as the wheel is centered by its connection to the axle hub. The lug nuts hold the wheel firmly to the mounting plate, but it is the wheel-to-axle connection that actually holds the weight of the car."

Then there's this:

"Even though we just spoke about hub-centric, in reality, it is the lug bolts that correctly centre the wheel. The hub and the centre bore of the wheel just takes us close to the centre quickly. If you have ever changed a wheel on a car, you would have noticed that the wheel fitting on the hub is mostly a clearance fit and is nowhere near to the precision levels required for accurately centring the wheel on the hub."

Someone called him out on it later, but he danced around it.


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PostPosted: Sun Nov 12, 2017 10:01 pm 
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Navy Lifer wrote:
Production "fit" is not as tight as is possible to achieve with aftermarket centering rings, and most OE tapered-seat wheels are considered to be a combination of hub-centric (to roughly center wheels with studs) and lug-centric (to bring the wheel into a concentric condition) on the hub.

Kevin, just as I stated earlier (quoted here), comments in the linked discussion make the similar point. Production hubs, rotors, and some wheels, typically being ferrous material, can develop rust and literally grow together, so there has to be "some" clearance to allow for that possibility. An enthusiast fitting wheels using hub-centric rings can make the clearance much tighter, with the recognition that doing so could potentially come with some downside, but the end result is that the wheel load is, in fact, shared and not carried totally by the 5 studs and lug nuts.

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PostPosted: Sun Nov 12, 2017 11:13 pm 
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Navy Lifer wrote:
Navy Lifer wrote:
Production "fit" is not as tight as is possible to achieve with aftermarket centering rings, and most OE tapered-seat wheels are considered to be a combination of hub-centric (to roughly center wheels with studs) and lug-centric (to bring the wheel into a concentric condition) on the hub.

Kevin, just as I stated earlier (quoted here), comments in the linked discussion make the similar point. Production hubs, rotors, and some wheels, typically being ferrous material, can develop rust and literally grow together, so there has to be "some" clearance to allow for that possibility. An enthusiast fitting wheels using hub-centric rings can make the clearance much tighter, with the recognition that doing so could potentially come with some downside, but the end result is that the wheel load is, in fact, shared and not carried totally by the 5 studs and lug nuts.


Okay, but the two statements are still contradictory. Either the hub centers the wheel or the studs and lugs do. It can't be both.


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PostPosted: Sun Nov 12, 2017 11:32 pm 
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I'm not looking to argue or disagree on your point--it may not be a matter of "both" actively centering the wheels, however, with a snug/press fit of a hub-centric ring or spacer, the wheel will be concentric before the lug nuts are ever installed. It requires the torque applied to the wheel fasteners to retain the wheel in dynamic conditions. Clearly, the tapered seat lugs, assuming the BC of the studs and wheel match, will also actively center the wheel. I do want to point out, once again, that Corvette wheels on a PPV are not being centered properly if wheel studs are the only means used.

The linked forum/board with that discussion is British, I think (actually it appears to be India)--the standards for hub-fit can be different among the many manufacturers around the world....we're only talking about one particular platform. If wheel fasteners are not tapered seat design, active wheel centering may be via the hub rather than studs/lugs.

In reality, it's more semantics than a matter of studs vs hub, if using close-fit centering rings. Otherwise, a production parts combination really does rely on the wheel tapers and fasteners for centering. How much actual contact exists between wheel center bore (ID) and the hub register (OD) is a variable that I haven't attempted to determine.

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PostPosted: Mon Nov 13, 2017 12:05 am 
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Navy Lifer wrote:
I'm not looking to argue or disagree on your point--it may not be a matter of "both" actively centering the wheels


How can you argue with it when it is most definitely not a matter of both actively centering the wheels? It's physically impossible. That's all I was trying to say. If you slide a wheel on a hub and it is a snug fit, it is centered by the hub. Installing the lugs is not going to somehow center the wheel even more. They are only providing clamping force at that point. If you slide a wheel on a hub and it is a sloppy fit, then the lugs are obviously going to be the only part centering the wheel. The hub is out of the picture. It just can't be both things centering the wheel.

Navy Lifer wrote:
a production parts combination really does rely on the wheel tapers and fasteners for centering.


I tend to agree with this, especially when you consider rusty hubs and wheel bores. I bet the wheels on 99% of the vehicles driving around, especially those with steel wheels in the northeast, are centered by the lugs alone.


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