Hopefully someone can clear this one up for me. A set of wheels arrived at work today for a customer's Fiat Bravo in 4x100 fitment complete with a set of wobbly bolts and 4 wobbly lockers. Problem was, the key for the lockers didn't match the bolts, leaving us 4 bolts short. We phoned every wheel supplier nearby, and the one place that didn't say "what's a wobbly bolt?" said not to bother with a 4th one and use a standard bolt instead. This was backed up by our own technical department, but this made no sense to me or the guy fitting the wheels. I know there's going to be hardly anything in it, especially when there's already 3 good bolts in there, but when it comes to the things that stop your wheels falling off, I'd rather be safe than sorry.
If anyone else has experience with this, professional or otherwise, I'd be interested to hear your thoughts.
The spigot ring makes sure that the wheel locates centrally, but the bolt wouldn't sit correctly in its seat, only one edge would get any kind of purchase. Not really ideal.
Personally I would not fit a 100mm PCD wheel to a 98Pmm CD hub.
I'm assuming that the wobbly bolts are designed to absorb the 2mm discrepancy. However I can't see how they do this without compromising the basic design strenght of 4 fixed bolts with solid centred tapered boss seats aligning exactly with the centres and seats of the wheels which in turn align exactly with the hub bolt hole centres.
You are right to be cautious about anything that stops wheels fallling off. I'd be very surpised is you will find in motorsport anybody using wobbly bolts and there is of course the insurance companies view!
I think the only 100% safe way of fitting 100mm PCD wheels to 98mm PCD hubs is to have the wheels offset drilled to 98mm and have the bolt and seat tapers changed to remove seat runout.
On a wobbly bolt, the seat moves independently of the head and the shaft, like a large washer. This lets the bolt seat correctly, whilst still lining up with the bolt hole. 4x98 wheels are rare, and the majority of Fiats and other Italian 4x98 cars you see around with aftermarket wheels will be using wobbly bolts. Doing this is completely safe, no corners are being cut, my issue is with saving a few coins by putting a standard bolt in with 3 wobbly bolts.
I fully understand what you say but I'm still puzzled.
On a 98mm PCD the center of the bolt is at 98mm. On a 100mm PCD it is at
100mm.
The bolts are 12mm in diameter and for 12mm the usual standard clearance hole would be 12.5mm.
On two diagonally opposed holes we would get 2 x 0.5mm, i.e. 1mm of play.
98mm + 1 = 99 and not 100mm.
So unless the wheel bolt holes are drilled out by +1mm over nominal bolt diameter the will be 1mm stress loading present.
The seats only start after the outer edges of the holes so yes floating bolt seats can align but the bolts can't, unless of course the wheel bolt holes are normally drilled to greater than +1.0mm nominal bolt diameter, and to my knowledge 0.5mm is the normal tolerance limit. This may mean that the majoriy of wheels will be greater than 0.5mm but it also means that some, even if a very low minority, will only be 0.5mm oversized and thus excess side loading and stress can be placed on the bolt shaft.
Not having purchased or analysed any 100mm PCD wheels with respect to fitting to 98mm PCD hubs I am of course theorising somewhat blind in the absence of absolute measurements. But at the moment logic suggests to me that this type of application is running very close to the limit of what would be sensible. However I do know for a fact that wheel bolts subject to any side load will fail without warning. With modern wheels lacking the old steel hub caps a sheared bolt head will not rattle around and thus raise the alarm. Instead the wheel will run with 3 bolts till the next fails. At
80mph the loss of one bolt with three remaining potentially side stressed bolts the whole system fails very quickly.
With respect to after market wheels Revolution, O.Z. and others have in that past readily supplied 98PCD wheels. Admittedly not all wheel mfgs. will supply 98mm PCD.
If they are designed to have 4 wobbly bolts I'd stick with it, even if you can fit a standard it may cause unessassry stress on the bolts and consequent failure. The consequences of any failure will at the very least be exensive, at worst fatal, not worth it for a few pounds per bolt.
MotorsForum website is not affiliated with any of the manufacturers or service providers discussed here.
All logos and trade names are the property of their respective owners.