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The magical snapping wheel fixings conundrum

4K views 26 replies 8 participants last post by  Cyruz 
#1 ·
Hopefully that sweet title grabbed your attention...

Right down to business. A couple of years ago I fitted some cheap (but not too cheap) Bola wheels to my 135i.



F: Bola B1 18x8.5 ET40
R: Bola B1 18x9.5 ET45

Not "hellaflush" (is that still a thing?!) but fairly wide for the car, it does have some light rubbing on the rears over large compressions. I ran around on them for around 4/5 months then on a long-trip out noticed a nasty rear vibration at speed, it got worse fairly quickly so I pulled over and found this.



At first I thought someone had tried to nick my wheels and got scared off halfway through and left them loose and they'd shaken to this point causing terrible stress on the bolts.



Also this was super fun to drill out :(



So I bought some replacement bolts, torqued them all to spec and went back to not worrying about it, thinking I was actually lucky to have caught this before it killed me. Skip forward another 4/5 months, same vibration, same sheared/shearing bolts. At this point I'm thinking that either the torque wrench is crap and is massively over/under tightening them (doesn't feel like it on the old bicep torque gauge though). Also I thought it's possible there isn't enough thread engagement so next step. Studs.

So I've converted all four corners to studs with bits from CA Automotive (lovely company btw with amazing staff). Now another 4/5 months go past and this time I'm checking the torque once a month because massive paranoia! Low and behold...



Thankfully snapped studs are a lot easier to extract than snapped bolts so at least they're easier to replace.

So that leads me to here... I'm lost for ideas. They're not too loose (stud spec is 85 ft/lb), comparing the wheel PCD to a spare brake disk, everything looks centered, center bore is correct and snug. I'm at a total loss for why the fixings just keep giving way over and over again. I've spoken to my mechanic (he's utterly confused), the wheel supplier (they've never seen anything like it 25 years of selling bits) and pretty much anyone else who will listen to me ***** about it. No-one has any answers.

I'm open to any and all theories at the moment, but preferably something I can test at home. I'm pretty much at the point of buying a new set of wheels at this stage and just writing off the money lost...

Important notes:
Only ever the rears, never had an issue on the fronts (both sides not just one!)
There is plenty of stud engagement
The studs aren't cheap eBay ones (and neither were either of the bolt sets)
The current nuts are steel (not crap Ebay Alloy ones!)

Final, final (seriously) point:
These should be under very little load, I'm not an engineer by trade but the studs/nuts/bolts locate the wheel, all the forces are on the centre bore, how am I even getting the forces required to snap steel studs is beyond me!

So please, anyone, save my sanity (and wallet!)
 
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#3 ·
marco_polo said:
Are the wheel bolt holes definitely 60° taper? Or radiused?
I will do a double check tomorrow on the wheels but I'm 99% sure they're 60 degree taper and the nuts are 100% 60 degree tapered (GT50 Steel wheel nuts from Driftworks, not sure if I'm allowed to link specific products from companies websites).
 
#10 ·
marco_polo said:
Rarebit said:
Those black lug nuts look like they have only been contacting the wheel a tiny bit..suggesting the taper isnt right
My thoughts exactly, a really weird banded witness.
Interesting... I've always gone with the idea that the supplied fixings with the wheels were correct (60 degree taper on them).

I think tomorrow I'll pull a front wheel off (as they never have any issues) and a rear wheel off. Check that the taper is the same and the factory haven't ****ed up when producing them and sent a mixed set of tapered and radiused wheels.

I'll also check the wear marks on the fronts vs rears.

Thanks for all the help so far guys!
 
#15 ·
If you have a vernier measure the part of the thread that the nut contacts and measure where they have snapped if they have thinned where they have snapped it's from over tightening but unlikely witch it being only the rears
The way that first one has snapped looks like fatigue to me so something is moving
The centre bore holds very little load while in use it's all done by the friction between the wheel face and disk face with the bolts clamping them together
 
#16 ·
Agreed, the centre bore's only job is to get the wheel running concentrically, shouldn't be load bearing.

I've run wheels before now without spigot rings fitted, takes a few minutes to clock them in with a DTI, but they don't move/wobble/vibrate once torqued up correctly.
 
#19 ·
The bolt in the first picture actually looks to have a shoulder worn in to it halfway down the taper.
The centre bore may be the right size, but is it making good contact with the spigot? I'm thinking either that the mounting face on the wheel might be not flat and bare (straight edge across to confirm) or the spigot hole in the wheel isn't mating right; it might be too far in the wheel if that makes sense?

The extra width of the wheel might be compounding the issue with the extra leverage. Once the wheel starts to shift you might be getting precession on the bolt threads and that may give them enough slack for the wheel to cockle over and cause the breakage.

The tapers might be the right angle, but not concentric with the threads in the hub, meaning you're not getting a good seat when tightening and side load is being applied to the bolts.
 
#21 ·
Thanks to help on here I've gotten to the bottom of it.

It's quite hard to see but the wheel nuts are hanging up on the shoulder and not making full contact with the taper. You can just about see their is a 2mm gap between the end of the nut and the bottom of the taper in the wheel face, so it's just not making full contact...



Unfortunately with how close the holes were drilled to the spokes in the wheel face there simple isn't room for the nut to locate properly down. I've got an idea on how to remedy this for a slightly longer temporary measure but in reality a proper set of wheels with good clearences probably shouldn't have this issue!
 
#22 ·
Have you tried going back to genuine wheel bolts?
Only reason I ask is I've had a set of Bola B1's on my e91 for the last 2 summers and never had an issue, done track days, autobahn, some daft abusive driving on some Scottish country roads n never had anything like this
 
#23 ·
Ginge said:
Have you tried going back to genuine wheel bolts?
Only reason I ask is I've had a set of Bola B1's on my e91 for the last 2 summers and never had an issue, done track days, autobahn, some daft abusive driving on some Scottish country roads n never had anything like this
Genuine bolts don't fit the wheels, the heads of the bolts are too large to fit a tool on to torque them up. I guess this is why Bola supplies inline drive nuts with them.

Since I'm converted to studs, it's not an option anymore either!
 
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