"WOBBLE" or "COLLAR" WHEEL BOLTS

[harrisj]

I have come across a wheel-retaining device in UK called a 'Wobble bolt' or 'Collar bolt'. It is a wheel bolt designed to accommodate a difference between a wheel PCD and a hub PCD. It is a bolt with a floating collar which can align itself eccentrically to the bolt axis by a millimetre or two. I haven't seen a drawing of the installation.

The context where I came across this device was fitting 100mm PCD rims to an Alfa Romeo 98mm PCD hub. It was allegedly 'approved' by the wheel distributor (but my guess is, probably not by Alfa).

What experience do eng-tipsters have of these?

Personally, I wouldn't touch them with a bargepole, especially on a high performance vehicle. But then, I'm a bit conservative when it comes to wheels falling off. I would also have a concern that my insurance company's eyes would light up if I have a claim.

 

[patprimmer]

I very much like my wheels to be retained and located by 5 conical faced nuts in matching cone shaped recesses in the wheel

Regards

eng-tips, by professional engineers for professional engineers
Please see FAQ731-376 for tips on how to make the best use of Eng-Tips Fora.

 

[GregLocock]

Yes, but I can see how to implement it. Once it is all clamped up and true (hmm) then I suppose there is not much in it, if done properly.

The potential for failing to fit it properly is of course immensely magnified compared with the standard design.


Cheers

Greg Locock

Please see FAQ731-376 for tips on how to make the best use of Eng-Tips.

 

[Fabrico]

Sounds about like the lug nuts used in the states on everything from 1 ton and up starting a few years ago when things got switched to hub-centric.

 

[Tmoose]

There was a time when US Mag wheels pretty much all used flat washers and flat faced nuts. As long as the wheel was centered by a bore piloting on a diameter on the hub it works just fine.

"Uni-lug" wheels had slots and offset inserts that presumably centered the wheels via the studs.

http://www.akhwheels.com/pages/images/akh063.jpg

http://www.themopardude.com/image/3911208.JPG

Un-Centered wheels are nothing but trouble

 

[izzmus]

To nitpick, Unilug centered the wheels via the shanks on the lug nuts, not the studs. They relied on a close tolerance between the lug slots and the lug nut shanks in order to keep the wheels centered. From what I have seen, no attempt was ever made to even remotely make the wheels hubcentric, meaning they need to be located by the lugs for balancing purposes.

Ford's F-series and "large" SUV truck line in the late 90's didn't even bother to center by the lugs *or* the hubs. (I do not know if they still use this design) Flat-faced lugs with serrated captivated washers, and rubber bands on the hub pilot as cushiony centering rings. That is, until they stopped bothering to put the rubber bands! After even a handful of thousand miles, the wheels will show evidence of walking around on the hub, but the fretting never seemed to get more severe than that, and I haven't heard of any problem with wheels falling off. Scary, yes, but millions on the road.

 

[Tmoose]

"To nitpick, Unilug centered the wheels via the shanks on the lug nuts, not the studs."

What, then, centered the lug nuts?

A near legendary vibration consultant told a story (one of many) that Ford asked him troubleshoot a persistent vibration problem in one of their car lines. Allegedly the consultant found that the bolt/stud circle was generated eccentrically on hubs or axles.
I never challenged his story, but always wondered how off center a bolt circle would have to be to force a typical hub centered wheel off center. This was certainly in the days of steel wheels and tapered lug nuts.

 

[GregLocock]

Meanwhile we machine our wheels off centre deliberately.

Enjoy.

Cheers

Greg Locock

Please see FAQ731-376 for tips on how to make the best use of Eng-Tips.

 

[CapriRacer]

izzmus,

I disagree about Ford wheels not being hub centric. I've been involved with them since the middle 1980's and they have always been hub piloted. I remember when they went to the clamp style lug nuts you described and my reaction at the time was that this was going to be an improvment because it eliminated the possibility that the tapered seat of the lug nut would pull the wheel off center.

 

[evelrod]

As to "what centers the uni-lug wheel"?
I have quite a few American Libre 13x7 wheels I use on my Lotus Cortina SCCA race car (now a vintage racer with VARA) that have the uni-lug slot pattern. It was a short cut so that the wheels could be used on both the Ford pattern and a Datsun 510 race car. The lug nuts, sleeve nuts, center the wheel by close fit at either end of the slot, depending which bolt pattern was being used. They work just fine and I have had no failures (of any kind, actually) in over 40 years!---They do look a bit odd to the uniniated and 'sleeve nuts' are very difficult to fit on occasion.

Rod

 

[Tmoose]

"Meanwhile we machine our wheels off centre deliberately"

Please, tell me more.


Thanks,

Dan T

 

[CapriRacer]

Perhaps I can help here!

If you were to measure the loaded runout of a tire, you would find that it varies around the circumference. This translates into an up and down motion of the axle - a vibration.

This variation is called "uniformity", but the terms "force variation" and "road force" are sometimes used as well.

You break this variation into sine waves of 1) one cycle per revolution, 2) Tw0 cycles per revolution, etc. These are labeled as "Harmonics" - 1st harmonic, 2nd harmonic, etc.

It turns out that the most influential harmonic for vibration is 1st harmonic.

Tire manufacturers can measure this non-uniformity and can mark the high point of the 1st harmonic.

If you were to measure the runout of a rim, you'd find the same sort of variation, but to a much lower degree - order of magnitude. My interpretation of this is that it is a whole lot easier to make something round out of metal than it is to do the same with a balloon.

But the important point is that you could measure the low point of the 1st harmonic of the rim and mark it as well. When you mounted the tire on the rim and matched those 2 points, the net effect is a "more round" assembly.

And since you can bore the centerhole of the rim off center with a reasonable degree of accuracy, you can then mark the low point by boring the valve hole there - which is the common practice.

BTW, we are talking pretty small values here. Off center boring is generally around 0.005", but it is enough to have a noticeable effect.

Not every rim is done this way and the amount is specified by the vehicle manufacturer, and the amount varies from vehicle to vehicle. Some vehicle manufacturers don't call for off center boring. Please note that for this to work, it absolutely requires hub piloting.

Needless to say, aftermarket rims are not done this way, particuarly considering that some rims fit a wide variety of vehicles, so the center bores are very large. Put another way, the rims are lug piloted.

So it is common (but not 100%) that OE tires and rims are measured and marked and matched mounted, but replacement tires and rims are not (but not 100%, either).

 

[GregLocock]

The giveaway is when you look at your new car - if the tires have two coloured spots on them then they are marked for tire force variaton AND balance, if only one then balance. Typically one of them will be lined up with the valve - that is TFV.



Cheers

Greg Locock

Please see FAQ731-376 for tips on how to make the best use of Eng-Tips.