Redrilling wheels - has this guy found the limit?

Yes, the reason spigot rings are needed for aftermarket wheels. But then with these posibilities maybe you can bolt on your wheel badly with a compressible plastic spigot ring and also have a non concentric fitment? So maybe a method of tightening which ensures concentricty is still needed?

People follow head torquing procedures set out by a manual, does the vw workshop manual give wheel torquing procedures?

Seat owners manual saying, hand tight with plastic screwdriver, then firmly with wheel brace in a diaganol pattern and then to get the wheel torque checked as soon as possible when using the spare in an emergency.

Maybe i've gone a bit over the top on the subject of wheel fitting now. I should go hide in a cave and stop reading this thread.

 

I'd like to question How strong is the spigot on the average car hub?

I try not to be a textbook engineer, I much prefer to be hands on and doing things. It's hard to quote experience within these things when you are 21, so to prove a point other sources have to be used, textbook/theory is a good starting place. I also do not aim or want to be an engineer who uses only textbook cases in design, unfortunately apprenticeship oppurtunities were extremely rare when I was 16 or 18, so A levels and a degree was what I settled for. Hopefully when I graduate I can find a job which will allow me to have hands on experience but also use the knowledge gained within textbooks.

 

Some aftermarket wheels...
Personally I'll not use any wheel that's not machined with the correct centre bore...but that's just me.

I want the wheel to be a snug fit on the hub, metal to metal, so the faces sit as square as possible before torquing the bolts up.

Not sure...
But anyone who makes up industrial flanges will know the procedure - nip them by hand equally, diagonally torque then chase them round in a circle to equalise the torque.

 

Your the engineer? Go work it out.

example for you too work out on paper if you wish.

Pug 205 rally car with alloy bell type discs fitted and wheel stud conversion. This means the drive flange spigot does not have enough protrusion through the thicker alloy bell to offer any support / centring of the wheel. Like this it would always loosen wheels the wheel nuts. When a new hubcentric spacer was installed it solved the problem. Lots of potential things going on there. You can of course jump on the easy option of the wheel not being tightened up concentrically if you wish.

 

I can appreciate you asking the questions as it shows a desire to learn and absorb information.
Your age means that I have been tightening bolts for double your life on this planet though. [:^(]

 

My paper said go with the easy option and say it wasn't concentric without the spacer. The hubcentric spacer fixed the problem, hands on approach sorted it out, no need for paper on a proven case. I was taught and most design books say, to design bolted joints which would not slip in normal conditions, transferring shear forces into the bolts. Therefore these should also not go onto the spigot.

My paper also said don't start working out how strong a spigot is in shear till you have stopped drinking beer.

 

No...the original point of the thread (which you asked to be revisited earlier, and I obliged) was as to the amount (or lack of) material left between the boltholes, and the centrebore.

It was never a question of concentricity or the need for spigot rings...

I gave my opinion on the that point, but you didn`t...care to now?

 

Regarding the machining of holes and bores in components:
It is impossible to machine two sets of diameters and bores, on two separately manufactured components, that are exactly concentric. There must always be clearance tolerances to permit them to fit together. The relationship between the centre bore of a wheel and the bolt holes is a good example of this. At any point during the assembly of components such as these, only two points in the system will align. ie. If you assemble a wheel on to a hub the wheel will touch the spigot at some point. When you introduce the first wheel bolt, the wheel will sit on the spigot and the bolt at that hole. Now, depending on the relative clearances between wheel/spigot and wheel bolt, when you introduce a second bolt, the wheel will either sit on the edge of the two bolts, or the edge of one bolt and the spigot. This continues until all the bolts are in, only two diameters are locating. When you tighten the bolts, the conical or hemispherical seating between wheel bolt holes and bolts takes over. Again, only two bolts will contact, but as you tighten, some seating occurs between wheel and bolt head due to the malleable material of the wheel (alloy), distortion in the wheel (thin steel) or bending in the bolt. At best, you will get a reasonable interface at all bolt head to wheel joints. Unless you mark up the wheel and hub, and only use the one wheel on the one hub, this will always happen.

I am pretty sure that the OZ wheels on ebay are what they appear to be.

Centre-lock wheels and not re-drilled.

Good examples of hubs to suit this very 'tight' arrangement can be seen on the following homologation sheets:

G2 Rallye Grp A - A5398 Page 38/Photo 8

G2 G60 Grp A - A5425 Page 24/Photo 8

G2 Rallye Grp A - A5295 Page 24/Photo 17

The photo and drawing above are a good example of how centre-locks go together.

In the photo, you will note the following:

I - Five studs which locate the disc bell.

II - A machined diameter close to the hub face.

III - A machined diameter close to the thread.

When you introduce the 917 wheel to the hub, three things happen:

The wheel locates on the spigoting diameter at II. This will be a relatively closer fit than that used in production wheels, as the tightening mechanism is in the centre and very concentric with diameter II.
It flops on to one of the five studs at I.
It is then supported by the diameter at III, to keep it square to the hub.

On the ebay OZ wheels, the second diamater is not required as the wheel is quite narrow and does not have the massive outset of this Porsche wheel.

When the centre-lock nut is introduced, the nut will tend to rotate the wheel, on the spigot, until one of the studs touches the sleeve inside the wheel at I. The sleeve will probably be steel.

As you continue to tighten the centre nut, the wheel will be stopped from rotating on the spigot by the stud, until the frictional resistance, between the inside face of the wheel and the disc bell, is great enough to carry the rotational load from the nut. At that point friction will take over until the nut is at the correct torque.

All forces imposed on the wheel by the road will be taken by this friction joint, up to the point where the loads imposed into the spigot thread exceed those induced by tightening the centre nut. If the frictional force is not overcome, then:

The maximum force seen by any one of the studs at I, is that induced during initial tightening. ie before friction takes over.

The maximum load seen by the spigoting diameter at II, is that induced during initial tightening. ie before friction takes over.

 

I have said on multiple occasions in the thread that I thought them safe to use. But with this new evidence from Dave maybe those holes aren't even wheel bolt holes and it is confusion borught about from a bad advert. Looking closer at the pictures it also seems that maybe they are not taper or radius seat bolt seats like I had assumed.

 

I have already pointed that out to you...

On the Porsche application explained by Dave, we see the studs used to locate/mount the brake disc. These have the dual function of preventing the wheel spinning when tightening the centre-nut. Therefore, it is assumed there are holes in the wheel(s) with a corresponding PCD.

My, question would be, though; why would such `locating holes` be straight through the wheel, where blind holes would suffice.

Also with the OZs in question, if the holes were intended merely for locating/prevention of spinning; Why would they appear to have a seating face like a bolt hole does?

So as interesting and informative as Dave`s info is, I would repudiate, that it`s not the case with the OZs in question.

 

StuMc,
compared with the very thick Porche wheel centres, the ones on the ebay OZ are relatively thin. Note how deeply over bored the Porsche stud holes are. It is much simpler to just drill through, then ream through, and fit the sleeve, in a thin section! Shallow blind holes mean that you have to set your drill and reamer extremely accurately. You would drill the hole deeper than you intend to ream, then ream out deeper than the sleeve you intend to fit.

Take a look at the VW Hubs, in the homologation sheets, on vwmotorsport.com. Chris has locked these documents, to stop German thefts, so I can't post the pictures. The studs are bullet headed and appear to extend beyond the edge of the centre nut taper?

 

Chiming back in to see where this thread has got to - and I'm not disappointed! Glad to see the heavy hitters have arrived with buckets of info

Firstly, I don't recall it being stated whether wheels sat on spigots, rather than them being an allignment tool. Plastic/metal irrelevant.

Post 128 above - cheers Dave for articulating how wheels can sit off centre & the tolerances which allow this.

Lastly, the point about the motorsport wheels and lugs sitting out. Centreblock wheels engage with what are effectively cut off studs, as locating / ? drive ? lugs. The OZ, pre- redrilling (I believe they're drilled Dave - the chamfer...) will have drillings on the back, like this:

 

I see your point, but the pics of those Dymags lend some credence to what I was thinking; Blind holes used purely to stop the wheel spinning as the centre-nut is done up. No apparent need for them to be sleeved (it would seem) since I guess the studs wouldn`t be impinging on them sufficiently long enough, nor with enough force to be a concern. That and being Mg motorsport wheels, they`ll be lifed, and termed `scrap` long before any impingement would be a problem.

 

Having done a little more research, I now offer the following.

The wheels, as Chris said in post #1, have been re-bored and chamfered, in the centre, to make centre locks from bolted wheels. I have some brake discs still from the four stud Audi 90 original assembly, these are 4 x 108. I have measured the centres as a comparison with the ebay photos. That centre bore in the ebay OZ wheels, must be at least 85mm.

These are present-day OZ Mg 'Rally' wheels. With insert sleeves, as the Compomotives on a prevoius post.



http://www.ozracing.com/at-team/wheels/rally-only/rally-neve/en

I take your points, regarding the need, or not, for sleeves in centre lock wheels. And, you are, of course, quite right. I was lead from the use of sleeves by Porsche, who for me, are the best car designers in the world, since Saab stopped making 96s!

This old dog appreciates the new tricks!

 

I`m sure he was of the opinion that they were centre-locks re-drilled for bolts...

If they were bolted, re-drilled for centre-locks, I`d be equally (possibly more) wary of the lack of material there, since this would now be taking a significant amount of the clamping force directly.

It`s just a shame it only seems to be `old dogs` who have the humility to concede to others` opinions/viewpoints...

 

I find these interesting.

It is not the correct torque that is determined by the lubricant, but the correct pre-load in the joint generated by a specific torque.

I have posted on other threads regarding lubricants used when torquing bolted joints.

The load induced in a threaded fastener, by a given torque, will depend on the lubricant, or lack of it, used. If you tighten an un-lubricated bolt, into an unlubricated threaded part, the load induced, in the bolt, could be as little as 40% of the load induced in a pair of threads treated with MoS2 grease.

Thus, wherever a torque figure is quoted, it should give reference to the lubricant to be used, or the torque figure is misleading!

The preload induced will also depend on the stiffness and relative thickness of the materials in the joint. If you are clamping an aluminum wheel, you will get less pre-load than if you are clamping a solid steel wheel, with the same torque. But, steel wheels are not solid, but pressed from thin sheet. They will flex. So, I assume that the pre-load is the same for both, as manufacturers don't quote different torque figures for aluminium versus steel. Or do they?

At the same time, if you have aluminium disc bells, the torque figure should be higher than for cast discs of identical thickness.

Porsches instruction to use copper grease is still not 100% informative, unless Porsche quote a specific manufacturer and specific part number for the grease. I presume Porsche give a Porsche part number for the grease, as VW do for specific lubricants in ETKA?

I have two copper greases:

Molyslip 'Coppaslip'. This has a very high copper content, it looks almost solid copper.

MoS2/Copper. This grease is very dark grey, with just a small pecentage of copper. I have had the tin so long, that the paper label has come off, and I dont know the brand or trade name.

I always use the 'Coppaslip', as I am sure the other grease was for a special application back in the day!

It is interesting that the brake disc hub still has the blue protective coating on it. To get maximum friction, in the joint faces, they should all be cleaned to bare metal, and have a surface finish of reasonably high value. I can't remember the figure at the moment, but 125 micron rings a bell.

So, I always clean the mating faces between disc/hub and between wheel/disc with 120 grade emery cloth. Note: Disc to hub should be cleaned and abraded or friction will be reduced.

The use of a lubricant on the spigot is sensible even for steel wheels. I have known steel wheels stuck on with rust.


Finally. I always used Mk1 GTI 9 spoke alloy wheels on every Mk1 we owned. These were of such a maleable alloy that after a time, the centre hole areas, adjacent to the bolt holes, would become deformed enough for the wheel to jam on the spigot. This is especially true when the wheels had been tightened, at a tyre depot, using an impact air wrench! I quickly learned a lesson, and now, I always take my torque wrench with me, and coppaslip, when I go anywhere near a tyre dealer!

Mind you, I guess that the four deformation bulges would take the loads into the spigot better for those who's spigots carry the wheel loads?

 

I have little personal experience of fitting centre lock car wheels, but from what I've seen, they use the same principle as centre lock motorbike wheels that are used on single sided swing arms.
I bought a pair od PVM Magnesium wheels for my 'bike years ago, including a centre lock fixing rear.

The hub provided the centre lock threaded part, tapered to seat the wheel centrally, it sat over 4 locating/drive 'pegs' and a large conical nut was used under the nut when tightening.



The inside of the rear wheel looked like the Dymag above, with it's multi-drilled blind holes.

 

They do indeed list a Porsche part number for a specific grease.
I just don't happen to have it. But, it is a copper based lubricant, and as you say, should be used with the torquing figures listed.

I have Coppaslip too, in addition to Castrol's Optimol.

 

If you can find the part number, I would be interested in purchasing some, to compare with what I have now!

 

The hub spigot looks very much like the 917 unit, with the two supporting diameters, as the wheel hub is obviously quite wide.

The four pegs can only locate, not drive. The friction face at the hub/wheel interface drives.

I doubt that the 'seats' were tapered. They would have been circular. Agreed that there is a tapered section between, the two locating diameters on the spigot, but this is only so the outer support diameter can be smaller than the inner centralising diameter. The outer one could be tapered as long as the wheel hub tapered bore was machined with enough clearance that nut would lift it away from the taper as it was tightened. Otherwise, the wheel would stick, and never reach the hub face.

If they are tapered, it really is going to be 'old dog - new trick'!