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-   -   PCD Variation Bolts (aka Wobble Bolts) - Myth versus Reality (https://www.team-bhp.com/forum/tyre-alloy-wheel-section/168043-pcd-variation-bolts-aka-wobble-bolts-myth-versus-reality-2.html)

Thank you

When installed on a vehicle, hub centric wheels are located directly off of the center flange of the brake drum or rotor. This means that the outer beads of the wheels are concentric with the wheel bearings which creates a much better balanced wheel and tire assembly. Aftermarket wheels usually have a standard center bore size to accommodate a wide variety of vehicles. Hub centric rings are rings that cover the spacing between the center bore of an aftermarket wheel to the hub of the vehicle. Hub rings are important because they secure the wheel in place and help prevent any type of vibration issue.

The recommended clearance hole for M14 is 15.5 mm. I find that the manufacturers usually use 5/8 inch drills which make a 15.87 mm hole, to be precise. Actually, the hole size is not really critical, as long as the bolt can comfortably pass through. All the clamping force is applied to the 60* taper in the alloy bolt hole by the 60* taper on the bolt.

Is there a similar solution ("Wobble Nuts"?) available for studs that most Japanese vehicles use? Bolts are more of a German/European thing, I gather.

In any case, I would concur with GTO in that the proper PCD wheel is the correct way to go.

Yes VCheng, there is.
The conical washer is the same like in the case of wobble bolt. And the final fastening happens with a regular flat nut against the conical nut that came along with the car.

I too have wobble bolts for a st of 100 PCD alloys in my 118NE.

Dear Patchyboy - this contraption has been around in the market for as long as I can remember. There were scores of Padmini taxies running around with these things when the wheel mounting holes used to enlarge due to rampant misuse / overload, mostly of taxies carrying fish! I would not use such things, wheel mounting is too critical a parameter to take chances with. If 98 pcd is a need, so be it, the wheel manufacturer must cater to this need. I am sure if he sees a market, he will cater.

On a similar topic, I also dread to see aftermarket alloy wheels having 8 and even 12 holes in them out of which only 4 are used. "Bhagwan Bachaye" (God save) the people who actually buy such stuff! I had the opportunity to visit an "alloy wheels shop" with one of my friends who desperately wants 7J/6.5J*15, 108pcd, +43mm offset wheels for his car. Before entering the shop, I had an understanding with my friend that I will not utter a single word. I kept quiet and thoroughly enjoyed the conversation, but after coming out, both of us had a hearty laugh! He is still searching, though! :D.

Best regards,

Behram Dhabhar

Do you have a link for a possible source? These would be very useful in certain cases.

www.ebay.com has got plenty of them. Might work easier for you. Double check the stud dia and pitch before you place the order. If you are upgrading steel rims to alloys, you might need longer studs as well. So measure the stud length as well, just in case.

I find a lot of people saying "I will not use this contraption" or "It is too dangerous", etc. I have tried to present my findings scientifically. I am on these bolts for the last 6000 kms, including a couple of high speed highway runs and have not noticed any vibrations or unusual behaviour. As a matter of fact, since I also upsized to 205 section from 195, the car is a lot more stable than before.

Can someone please care to explain scientifically as to why these bolts are unsafe, so the less knowledgeable folks like me can benefit?

Dear Patchyboy - I understand your comment above and I empathize with it. I have to say only one thing. Nobody (and that means nobody) must deviate from sound engineering principles. Just because a thingy works for 6000 kms does not mean that it becomes engineered. The best case is that of dilapidated Premier Padmini taxies in Mumbai. Some of them still work. Its a wonder that they still go from point A to point B! Wheels and tires are the most important part of any car. Nobody must take any chances.

Best regards,

Behram Dhabhar

Thank you for the kind response. People upsize tyres, use wheel spacers, stiffer struts & springs, etc. All of them alter the wheel geometry. But none face as much criticism as these bolts do. I would be quite happy to see some counter arguments explaining why these are unsafe with scientific explanations. All that I have come across so far, here and elsewhere, is that people refuse to use it, as they *think* it is unsafe. I have not seen even one single post where people have reported these bolts to have failed, including on the racetrack. If a company as reputed as OZ Racing manufactures these, then I feel it is sound engineering and no chances have been taken.

I have used them for 6000 kms, but a few of my friends elsewhere, based of whose advice I went for these bolts, have been using them for several years for more than a few tens of thousands of kilometers and they are doing just fine. Trust me when I say this - if I could find a 98 PCD alloy wheel with a design that appealed to me, quality that made me feel good and at a cost that I could afford, that would have been my first choice. Why would I want to spend close to 1 lakh rupees of my hard earned money on this upgrade and still make do? It is the lack of a suitable option, added with the scientific reasons presented in the OP, that made me choose this option.

Coming from a person of your stature, I expected a more scientific explanation and not empathy. There is nothing emotional about this. Thanks anyway.

Dear Patchyboy - I reiterate my statement, word-by-word, line-by-line. By doing so, I might unknowingly save somebody's life. As a professional, I do not have any emotional connect about this. With your kind permission, I would like to end this series of conversation here.

Best regards,

Behram dhabhar

Sir, It's great to have you weighing in on this. I know you've mentioned you'd like to end this conversation, but if you could indulge me this one time: this particular case is about a PCD increase from 98 to 100, i.e. a diameter increase of 2mm. More precisely, it means just a 1mm deviation of each lug, from original (since the radius increase would be just 1mm, for each lug). I wanted to understand if the 1mm deviation is material enough, in the case of a tyre, where some play is already built in, by design, for ease of being able to replace tires, for example.

I completely agree with you on the general engineering principle, but if you could look at this specific instance 1) this is a specific case of a 2mm increase in PCD 2) a non-performance car for general use, not a performance car to be used in strenuous environments such as on track or for rallying.

I don't have a Linea nor do I even need to consider this, but from the POV of understanding cars and given your engineering experience, it would be great if you could weigh in on this please:

Dear Bosporus - hello to you. I understand your query. Let me explain:

This thread started on 10 September this year. For every 1000 people who have read this thread so far (8587 people have read it to-date), only 3 people have replied to this thread so far (25 people have replied to-date), which works out to only 0.3% of the population. I am writing for that 8587 or 99.7% of the population who read, because they have genuine auto-passion in them and they look forward to receiving the correct direction. I shall never write anything which deviates from this primary need. I very well know the "madhouse" in which we live. In "our" way of working (:)), comments can be construed in many different ways, which is not correct. I hope I have answered your query.

I was casually discussing this with one of my friends over lunch and he gave me a very simple analogy. He asked me to ask on the forum "if I give 98 rupees to a TeamBHPian, will he give me 100 rupees immediately"? We had a hearty laugh! Then I told him, "let's make it 98 lakhs and 1 crore"! I'll get my Harley Davidson for the price of a Bullet (that I just don't have 98 lakh rupees is a different matter altogether). Hahaha!

lol:.

Best regards,

Behram Dhabhar

Summarizing findings -

For -

• Manufactured by a reputed company & TUV Certified
• Am using for past 6000 kms without issues
• Friends who recommended have been using for more than 100K + kms without issues
• All the reasons described in the OP

Against -

• Sounds dangerous, will not use
• I don't think these are safe
• Irrelevant analogies
• It is a critical component. So should not experiment

Can we all please be objective and provide some engineering principles as to why these are a bad idea?

So I get from this thread that one should never try to fit an alloy where the PCD does not match the original wheel spec from the manufacturer, it is unsafe.
I guess this is what DHABHAR.BEHRAM is maintaining.

What PatchyBoy is interested in is knowing that if one goes in for a PCD mismatch (which is inherently dangerous), do these wobble bolts offer higher safety than using the straight bolts. (I am inclined to think that indeed they offer higher safety than using the OEM ones).

Now I have one issue with the wobbly bolts, the center line of the seat (the wobbly bit) and the center line of the bolt will never coincide.
Won't this lead to vibrations? Won't the vibrations, over a period of time, lead to loosening of the bolt or the stresses lead to cracks?

No. I want to know why people consider these bolts to be unsafe. I beg to disagree with the bold part. I am convinced that done right, this setup is only as dangerous as the OE setup, unless someone provides me with scientific evidence proving otherwise. After all TUV certification does not happen that easily.

Stress cracks and bolt loosening will happen if the bolts are not tightened to manufacturer specified torque, both with these bolts as well as with OE bolts. The bolts can only fail if the shear forces overcome the clamping forces and that is impossible, if the bolts are torque correctly.