Wobble Bolts

Wobble Bolts

Author
Discussion

mat777

Original Poster:

9,293 posts

129 months

Thursday 29th November 2012
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I had never heard of these before someone mentioned them to me this morning, but they are apparently the "in" thing for fitting different wheels to cars with a very-similar-but-not-quite-the-same wheelbolt pattern. They look like this:



From an engineering/structural perspective the idea horrifys me, but what does the PH collective make of them?

Disco You

3,460 posts

149 months

Thursday 29th November 2012
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Popular with chavs fitting the wrong wheels to cars...

kambites

62,176 posts

190 months

Thursday 29th November 2012
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It's rather have to tell, really.

By the look of it, it's essentially just a bolt going through a hole bigger than the outer thread diameter and plenty of structurally important bits of car use that mechanism for attachment. On the other hand, there can't be much of an overlap stopping the bolt head from pulling through the hole.

I suppose they're probably good enough to do the job.

C.A.R.

3,719 posts

157 months

Thursday 29th November 2012
quotequote all
It has come up in the past.

Generaly PH collective think that they're a potentially dangerous idea.

Then you'll always get 2-3 people who own Volkswagens who will defend the practice of using wobble bolts because there's no evidence of them having caused an accident yet (so it must be OK then).


Krikkit

22,113 posts

150 months

Thursday 29th November 2012
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It all hinges on how much overlap you have between the stud inside and the nut outside. If it's a decent amount then there's no problem. Don't forget the bolts aren't holding the weight of the car, just stopping them coming off the spigot.

Triumph Man

7,414 posts

137 months

Thursday 29th November 2012
quotequote all
C.A.R. said:
It has come up in the past.

Generaly PH collective think that they're a potentially dangerous idea.

Then you'll always get 2-3 people who own Volkswagens who will defend the practice of using wobble bolts because there's no evidence of them having caused an accident yet (so it must be OK then).

I own a Volkswagen and I think wobble bolts are a terrible idea. I see on UKP quite regularly people advocating their use, though.

kambites

62,176 posts

190 months

Thursday 29th November 2012
quotequote all
Krikkit said:
Don't forget the bolts aren't holding the weight of the car, just stopping them coming off the spigot.
No, but they are taking the drive and braking forces. Unless I'm missing something, the only thing stopping the wheel from rotating around the spigot as far as the potential play in the bolt will allow, is the friction between the back of the bolt-head and the washer section? If that interface does start to move, I can't see the bolt retaining its tightness for long.

aponting389

642 posts

147 months

Thursday 29th November 2012
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kambites said:
No, but they are taking the drive and braking forces. Unless I'm missing something, the only thing stopping the wheel from rotating around the spigot is the friction between the back of the bolt-head and the washer section?
plus the friction of the wheel on the hub... which is huge compared to that of the bolthead/'washer section'

never used them but cant see much wrong with them... as long as you have all 4/5 torqued equally

kambites

62,176 posts

190 months

Thursday 29th November 2012
quotequote all
aponting389 said:
kambites said:
No, but they are taking the drive and braking forces. Unless I'm missing something, the only thing stopping the wheel from rotating around the spigot is the friction between the back of the bolt-head and the washer section?
plus the friction of the wheel on the hub... which is huge compared to that of the bolthead/'washer section'
Ah of course, yes. Good point. smile

mat777

Original Poster:

9,293 posts

129 months

Thursday 29th November 2012
quotequote all
doogz said:
mat777 said:
From an engineering/structural perspective the idea horrifys me, but what does the PH collective make of them?
Actually, what's your take on it. Where do you think they'll fail/cause issues?
Because you are putting a huge amount of asymmetric force on the head of the bolt every time you go round a corner and the wheel is trying to come off the hub - a good way to potentially bend the bolt or even pull the head off by inducing a stress crack that gets larger over time

mrmr96

13,736 posts

173 months

Thursday 29th November 2012
quotequote all
kambites said:
Krikkit said:
Don't forget the bolts aren't holding the weight of the car, just stopping them coming off the spigot.
No, but they are taking the drive and braking forces. Unless I'm missing something, the only thing stopping the wheel from rotating around the spigot as far as the potential play in the bolt will allow, is the friction between the back of the bolt-head and the washer section? If that interface does start to move, I can't see the bolt retaining its tightness for long.
Don't let Captain Muppet hear you saying that!!

http://www.pistonheads.com/gassing/topic.asp?h=0&a...

kambites

62,176 posts

190 months

Thursday 29th November 2012
quotequote all
doogz said:
Not sure what you mean by 'back of the bolt-head and the washer section' though?
These things are basically a washer which is machined to fit the profile of the wheel and a separate (smaller) bolt that goes through it, right?

As aponting389 said above though, it shouldn't be an issue because of the massive friction area between wheel and hub.

aponting389

642 posts

147 months

Thursday 29th November 2012
quotequote all
mat777 said:
Because you are putting a huge amount of asymmetric force on the head of the bolt every time you go round a corner and the wheel is trying to come off the hub - a good way to potentially bend the bolt or even pull the head off by inducing a stress crack that gets larger over time
total rubbish

big_boz

1,684 posts

176 months

Thursday 29th November 2012
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This looks ludicrous, how can these be legal?

I can not fathom what would possess someone to want to put their life and the risk of others in the hands of something like this.

Captain Muppet

8,537 posts

234 months

Thursday 29th November 2012
quotequote all
kambites said:
Krikkit said:
Don't forget the bolts aren't holding the weight of the car, just stopping them coming off the spigot.
No, but they are taking the drive and braking forces. Unless I'm missing something, the only thing stopping the wheel from rotating around the spigot as far as the potential play in the bolt will allow, is the friction between the back of the bolt-head and the washer section? If that interface does start to move, I can't see the bolt retaining its tightness for long.
The friction is generated by the bolt preload. Until that friction is overcome the bolts (and the spigot if there is one) will see no shear load. It's the reason that greasing the hub face makes me shudder.

The whole "spigot takes load" thing is bunk. Spiggot rings are often plastic, and on some vehicles don't exist. They are a location aid for assembly. If there were meant to take load they wouldn't be relying on 3mm of engagement in to a soft aluminium casting.

kambites

62,176 posts

190 months

Thursday 29th November 2012
quotequote all
big_boz said:
This looks ludicrous, how can these be legal?

I can not fathom what would possess someone to want to put their life and the risk of others in the hands of something like this.
But that's the question - why do you think it's dangerous? What failure mechanism would cause it to fail where a normal bolt wouldn't?

kambites

62,176 posts

190 months

Thursday 29th November 2012
quotequote all
Captain Muppet said:
The whole "spigot takes load" thing is bunk. Spiggot rings are often plastic, and on some vehicles don't exist. They are a location aid for assembly. If there were meant to take load they wouldn't be relying on 3mm of engagement in to a soft aluminium casting.
True - it's a right bd to put a wheel on without one.

So what's you take on these bolts? From what's been said so far, I don't really see a problem with them as long as the head of the bolt is enough bigger than the washer hole that all sides of the head are always making good contract with the washer.

aponting389

642 posts

147 months

Thursday 29th November 2012
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the bolts are no different to some that are fitted OEM to various cars. they just have a bit more float on the seating washer

kambites

62,176 posts

190 months

Thursday 29th November 2012
quotequote all
doogz said:
I'm with Matt on this, I think cracking of the bolt, due to fatigue from bending more than any sort of failure of materials due to yield/shear/tensile failure is more likely.
Why would the bolt bend? The head is still set against a flat surface parallel to the hub.

Big Rod

5,915 posts

185 months

Thursday 29th November 2012
quotequote all
kambites said:
big_boz said:
This looks ludicrous, how can these be legal?

I can not fathom what would possess someone to want to put their life and the risk of others in the hands of something like this.
But that's the question - why do you think it's dangerous? What failure mechanism would cause it to fail where a normal bolt wouldn't?
Y'know what, these used to make me shudder but having thought about it, other than the chamfer/washer being a little offset, there's nothing different about these compared to normal bolts.

The way I see it, aslong as the hub is centred correctly they're no worse than any other wheel bolt.