Wheel Hub Threaded Stud Conversion - Safe?

[spoon]

I created this thread to promote an important discussion that was brought up. Some of you may be aware, but I converted my wheel hubs to 4x100, and did so in a manner not typical of other Fiesta ST owners.

My new hubs were drilled by Alex, as many of yours are. The difference lies where I had him drill two extra sets of holes, one @ 4x100 and another @ 4x108. I also had him thread these holes to M12x1.5 and am using threaded studs from Turner motosports, found here.

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Question:

What's the engagement on the threads there? Not sure what kind of load those threads would see, maybe it's not a big deal but for some reason the conversion makes me nervous. Have you seen this conversion on other hubs? Did some google-ing and didn't find much.

Very good question. Of course the studs won't break, right... but the threaded hubs we should think about? Hmm. I'm not an engineer, but I do have engineer friends and they assured me this conversion is more than fine, particularly that there are no real tensile loads that will be applied to the studs or threaded holes that will cause a catastrophic fail, other than maybe in a really bad wreck. And in really bad wrecks, we've all seen the wheels fall off. Another thing to consider is our use of hubcentric rings... which squarely put load on the vehicle hub and not the wheel studs, and also these parts being steel. I do not know what type of steel our hubs are constructed of, unfortunately. Maybe an engineer can chime in.


Experience:
That said, I have personally used threaded studs (Bimmec, Turner, ARP, and MSI) on various Volkswagens and Audis, albeit all of which makes and models came from factory with threaded hubs, meaning that the hubs were "engineered" with this for the purpose of using wheel bolts, just like your E36. I would guess it to be the case, but I cannot confirm the thickness of the VW and Audi hubs. I want to say that my VW hubs were no more thicker than my Fiesta hubs, used the same studs, and were likely made of the same exact material although I can't really confirm the last bit. The Audi hubs were hefty I do remember that, as my cars were AWD monsters that weighed over 2 tonnes. You bring up a good point that does spark some curiosity though, because our cars were not "engineered" purposely for this. Let's examination...


Data:
I could have used any thread pitch, but I kept our factory M12x1.5. According to the internets, that is 16.9 threads per inch (TPI).

I happen to have the original hubs sitting right here next to me. They measure at exactly 9mm thick. 1" = 25.4mm.

25.4 / 9 = 2.8

16.9 (TPI) / 2.8 = 6 threads of engagement.


Popular opinion:
My engineer friends tell me that 6 threads engaged is a safety factor of 2. So with all that, and I never really thought about how safe it would be other than they are steel studs threaded into a steel hub and should be plenty safe having 6 full threads of engagement, so still I know that I am kinda the guinea pig here. With the studs, I've already hit curbs all around Laguna Seca, and have a track day at Sonoma in two weeks, we'll see how they do.

I also found this chart on the internet too. Maybe there's an engineer or two on the forums that can chime in to confirm. [emoji481]

Let's chat!

 

[spoon]

Here is a photo of a finished hub, by Alex:

 

[OffTheWall503]

That looks like a very nice conversion, I would have no worries about doing this when done properly.

 

[RAAMaudio]

Very good idea even if I do not like bolts like BMW uses, I converted to studs from Turner and still have a set around here somewhere.

I did have an issue with threaded studs working loose on track so I spot welded mine in but likely that was not a real concern and not based on any real experience, just a thought and action following it.

That said, I like this a great deal and having both bolt patterns one could use both far more easily than pressed in studs.

Way F'in cool

 

[OffTheWall503]

If I do a conversion it will be this way so all I need to do is change the studs to give myself either pattern.

 

[M-Sport fan]

The ONLY way I would ever do a 4x100 conversion is if we could get BLANK hubs to fit our cars, and then have Alex drill ONE pattern of 4x100 PCD threaded holes in them.

I have heard ALL of the testimonials to how indestructible multi-drilled hubs are on our cars, yes, even over track curbing, and on 00-50 tread wear road race slicks, but I still do not trust them (it's just ME, so no need trying to convince me otherwise ).

 

[RAAMaudio]

I have hubs from another car that are less substantial than the flanges on these hubs and they have 4 large holes in them besides the factory stud location, they came that way, I used them on a race car with 265 wide slicks, as my style pounded over the curbs, etc....no problems. Drilling more holes is not going to make a difference I am sure but do as you wish of course

 

[spoon]

I don't need to take engineering classes to know that there is more metal between the lug holes than there is between the edge of a lug hole and the OD of the actual hub.You'll find that not all of that metal between the lug holes is necessary to prevent the part from destroying itself. By this logic, the part is not becoming any weaker by the addition of various holes.

Not only that, but my engineering team created a cad model for teh hub and ran an FEA on the thing. It's more than fine.

 

[RAAMaudio]

Spoon,
Thanks for the post, having substantiated what many of us know is a great help to those wanting to do mods that may not always be acceptable to others for whatever their personal reasons dictate.

Experience matters a great deal, one does not always need to be an engineer to figure things out, my favorite story is about somebody I know who is the head QA at huge rocket manf plant, everything goes through him for approval, decades of experience, no degree.

 

[M-Sport fan]

I am NOT trying to dissuade anyone from doing this, as yes, both the engineering AND practice has been found to be TOTALLY 'safe and sound' (as long as all of the drillings are chamfered properly to prevent stress risers).

It is just MY "personal reasons", as Rick says, which keep me from wanting to do this mod, this way.

 

[xvxax]

Hey thanks for the write up. I like talking about weird stuff like this. Are there any threads at the back of the hub surface? If not, probably safe enough.

I did have an issue with threaded studs working loose on track

Did you use loctite? I remember I used loctite red with some level of heat tolerance on my studs. One kinda funny thing I remember about different stud manufacturers was that different manufacturers used different torque values for the studs. I think the first vorshlag set I used I torqued to like 15lb/ft via the allen keys at the top of the studs, but other guys required like 75lb/ft and double nut method for their studs. It was all over the place. What did you torque the studs to, did you use loctite?

One kind of thought I had about this coversion is a bolt on rotor manufaturer, 10.9" rotors were popular with early japanese cars but I haven't been able to find specs for rotors. Not sure if it matters much, but a bolt on rotor solution would be pretty awesome.

 

[RAAMaudio]

It was quite a few years ago, many cars, hundreds of mods since then, pretty sure I used loctite but not absolutely sure.

I found a set of the studs in storage last fall, another set that were tact on but never used them, not going to use them myself so if I find them I will let it be known in case somebody wants a deal on some.

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By bolt on rotor are you meaning two piece rotor and hats?

It seems I at least heard of something being offered but not sure where I saw it, some time ago.

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I also saw a WW bbk with AP Racing rings I am searching for, I would love to have AP rings on my front BBK, WW GT race are more than fine on the rear and doing well up front so probably do not need them. I really like AP, had them for my last race car build.

 

[spoon]

Hey thanks for the write up. I like talking about weird stuff like this. Are there any threads at the back of the hub surface? If not, probably safe enough.

You're welcome!

There is probably half a thread hanging out of the back of the hub. I see where you are going with that question. If all the threads on the stud are engaged, it doesn't at that point matter how thick the hub flange is or how many threads deep it is.

I would still question how strong the actual hub itself is, being that I don't know what material it is constructed out of. I just know it's steel. And steel hurts when you hit your head on it.

For this, I know I am the guinea pig... I have track days lined up for months so the parts will go through some paces. Put a couple thousand miles on them so far. Hit a few potholes, ugh.

Ford dealership saw them too, didn't even mention it. :O

Did you use loctite? I remember I used loctite red with some level of heat tolerance on my studs. One kinda funny thing I remember about different stud manufacturers was that different manufacturers used different torque values for the studs. I think the first vorshlag set I used I torqued to like 15lb/ft via the allen keys at the top of the studs, but other guys required like 75lb/ft and double nut method for their studs. It was all over the place. What did you torque the studs to, did you use loctite?

I screwed the studs in by hand, and used an allen key to tighten, if I were to guess 10ftlb? When removing wheels, yes, I have had a stud loosen a bit, in which case I grab the Allen wrench and tighten again to 10ftlb. And I do not use Loctite. Everyone has their own preference but I found it to be a waste of time (for me) and I will give two reasons why I feel this way, of course keeping in mind that what works for me, may not work for everyone:


1: Even with Loctite red, the studs come loose on track days when swapping race wheels for your street wheels at the end of day. The brake/wheel temps incurred after the track sessions are plenty high enough to loosen grip of even the higher-temp versions of Loctite, in my experience. FWIW, I personally have yet to find any loose nuts between sessions. Of course, torque wheels between sessions as always, just like you were running stock studs.

and

B: If you're going to be swapping your studs back and forth between bolt patterns, say, just twice per year for seasons change, Loctite probably won't be the worst idea. But if you are swapping bolt patterns often, changing wheels often, or tracking, I would say that you would be better served keeping the threads as clean as possible and not using Loctite. Loctite can kinda gum up the threads a bit after multiple removals and reapply, so I personally use nothing.

YMMV, of course!