Kwik-fit and a puncture.

#11

On Tue, 10 Nov 2009 18:54:42 +0000, Conor wrote:

Quote:

In article <ZsiKm.17$uh1.10 (AT) newsfe20 (DOT) ams2>, Chris Whelan says...

By what process would a wheel bolt, tightened to the correct torque,
become significantly less tight?

When the wheel heats up during the journey. Or do you drive a magical
car where the brakes don't get hot?

I've never experienced the wheel nuts on any car I've owned becoming
loose by a process of the brakes becoming hot, no. And that includes some
experience of motor sport where the discs would glow bright red!

The manufacturer would have taken into account thermal and other effects
when deciding a suitable tightening torque, otherwise we would be seeing
the country brought to a halt by unintentional three-wheeled cars
stranded at the roadside.

I'm aware of vehicles in regular use that have not had the wheel nut
torque checked for perhaps three or more years.

From experience, I think it far more likely that the problem would be one
of removing the wheel nuts of those cars, rather than them becoming
significantly loose!

Chris

--
Remove prejudice to reply.

#12

In article <hdccgi$5er$1 (AT) news (DOT) albasani.net>, roger20nospam (AT) ntlworld (DOT) com
says...

Quote:

"Chris Whelan" <cawhelan (AT) prejudicentlworld (DOT) com> wrote in message
news:ZsiKm.17$uh1.10 (AT) newsfe20 (DOT) ams2...
On Tue, 10 Nov 2009 18:06:00 +0000, Harry Bloomfield wrote:

Dave Plowman (News) used his keyboard to write :
BTW, congrats to Audi for giving the wheel bolt torque in the driver's
handbook. 120 Nm If only they took their own advice - it was nowhere
that tight when I took it off.

They can settle in a little, especially so on a new car. The advice is
to recheck them after a period.

By what process would a wheel bolt, tightened to the correct torque,
become significantly less tight?

Chris

--

Every garage and manufacturer and main dealership must be wrong. If you
don't know the answer then you might as well give up !
Still, it's given us all a laugh.
On this odd occasion, Kwik Fit was correct. Did you get a receipt from the
garage that did the puncture repair as you might need it for a legal claim
against them in the future.

By what process do you divine that Kwik fit were correct?

#13

Harry Bloomfield wrote:

Quote:

Dave Plowman (News) used his keyboard to write :
BTW, congrats to Audi for giving the wheel bolt torque in the driver's
handbook. 120 Nm If only they took their own advice - it was nowhere that
tight when I took it off.

They can settle in a little, especially so on a new car. The advice is
to recheck them after a period.

Am I being daft - or does it not take less force to UNDO a nut than to

tighten it? If it takes 120 Nm to get as tight as you like, does it take
120Nm to get it undone again? Not something I've ever tried, but its
never occurred to me to use a torque wrench to undo a nut....

#14

Chris Whelan wrote:

Quote:

On Tue, 10 Nov 2009 18:06:00 +0000, Harry Bloomfield wrote:

Dave Plowman (News) used his keyboard to write :
BTW, congrats to Audi for giving the wheel bolt torque in the
driver's >> handbook. 120 Nm If only they took their own advice -
it was nowhere >> that tight when I took it off.

They can settle in a little, especially so on a new car. The
advice is to recheck them after a period.

By what process would a wheel bolt, tightened to the correct
torque, become significantly less tight?

Chris

New studs and can stretch , wheel rims bed when put under load ,
subject to heat , cold etc for the first time .

#15

Paul wrote:

Quote:

Harry Bloomfield wrote:
Dave Plowman (News) used his keyboard to write :
BTW, congrats to Audi for giving the wheel bolt torque in the
driver's handbook. 120 Nm If only they took their own advice - it
was nowhere that tight when I took it off.

They can settle in a little, especially so on a new car. The advice
is to recheck them after a period.

Am I being daft - or does it not take less force to UNDO a nut than to
tighten it? If it takes 120 Nm to get as tight as you like, does it
take 120Nm to get it undone again? Not something I've ever tried, but
its never occurred to me to use a torque wrench to undo a nut....

you need far more force to undo, mainly because of friction and corrosion,
using a torque wrench to undo would not give a meaningful result and might
overload and damage the accuracy of the torque wrench. in addition most
people do not understand how to use a torque wrench to re-check the
tightness of a bolt.

#16

Mrcheerful wrote:

Quote:

Paul wrote:
Harry Bloomfield wrote:
Dave Plowman (News) used his keyboard to write :
BTW, congrats to Audi for giving the wheel bolt torque in the
driver's handbook. 120 Nm If only they took their own advice - it
was nowhere that tight when I took it off.
They can settle in a little, especially so on a new car. The advice
is to recheck them after a period.

Am I being daft - or does it not take less force to UNDO a nut than to
tighten it? If it takes 120 Nm to get as tight as you like, does it
take 120Nm to get it undone again? Not something I've ever tried, but
its never occurred to me to use a torque wrench to undo a nut....

you need far more force to undo, mainly because of friction and corrosion,
using a torque wrench to undo would not give a meaningful result and might
overload and damage the accuracy of the torque wrench. in addition most
people do not understand how to use a torque wrench to re-check the
tightness of a bolt.

Corrosion aside, that just seems to be 'anti' common sense..

Tightening, you are overcoming (increasing) friction and trying to make
a piece of steel longer than it wants to be - so two components to the
force in Nm required to get the nut to where you want it.

Loosening, you need to overcome the same friction (decreasing) but do
not have the stretching element of the material..

So in principle, if you tighten up new, greased nuts on a thread and
then immediately take them off using a torque wrench - it should take
less effort?
This just seems so obvious, i can see I'm going to have to have a go to
test the theory. ;-)

#17

Paul wrote:

Quote:

Mrcheerful wrote:
Paul wrote:
Harry Bloomfield wrote:
Dave Plowman (News) used his keyboard to write :
BTW, congrats to Audi for giving the wheel bolt torque in the
driver's handbook. 120 Nm If only they took their own advice - it
was nowhere that tight when I took it off.
They can settle in a little, especially so on a new car. The advice
is to recheck them after a period.

Am I being daft - or does it not take less force to UNDO a nut than
to tighten it? If it takes 120 Nm to get as tight as you like, does
it take 120Nm to get it undone again? Not something I've ever
tried, but its never occurred to me to use a torque wrench to undo
a nut....

you need far more force to undo, mainly because of friction and
corrosion, using a torque wrench to undo would not give a meaningful
result and might overload and damage the accuracy of the torque
wrench. in addition most people do not understand how to use a
torque wrench to re-check the tightness of a bolt.

Corrosion aside, that just seems to be 'anti' common sense..

Tightening, you are overcoming (increasing) friction and trying to
make a piece of steel longer than it wants to be - so two components
to the force in Nm required to get the nut to where you want it.

Loosening, you need to overcome the same friction (decreasing) but do
not have the stretching element of the material..

So in principle, if you tighten up new, greased nuts on a thread and
then immediately take them off using a torque wrench - it should take
less effort?
This just seems so obvious, i can see I'm going to have to have a go
to test the theory. ;-)

the friction is the problem, when tightening you have the mating surfaces
already sliding and it easier to keep them sliding than it is to re-start
them sliding, especially in the opposite direction, the metal itself acts a
bit like a one-way clutch.
How about this for an analogy: Imagine two pieces of spiky carpet (giant
size version of the faces of the nut and wheel) if you were to rotate and
compress the carpet then the fibres would all get squashed and interlock, to
undo in the opposite direction you have to overcome the bent fibres and get
them going the other way.

#18

Mrcheerful wrote:

Quote:

Paul wrote:
Mrcheerful wrote:
Paul wrote:
Harry Bloomfield wrote:
Dave Plowman (News) used his keyboard to write :
BTW, congrats to Audi for giving the wheel bolt torque in the
driver's handbook. 120 Nm If only they took their own advice - it
was nowhere that tight when I took it off.
They can settle in a little, especially so on a new car. The advice
is to recheck them after a period.

Am I being daft - or does it not take less force to UNDO a nut than
to tighten it? If it takes 120 Nm to get as tight as you like, does
it take 120Nm to get it undone again? Not something I've ever
tried, but its never occurred to me to use a torque wrench to undo
a nut....
you need far more force to undo, mainly because of friction and
corrosion, using a torque wrench to undo would not give a meaningful
result and might overload and damage the accuracy of the torque
wrench. in addition most people do not understand how to use a
torque wrench to re-check the tightness of a bolt.

Corrosion aside, that just seems to be 'anti' common sense..

Tightening, you are overcoming (increasing) friction and trying to
make a piece of steel longer than it wants to be - so two components
to the force in Nm required to get the nut to where you want it.

Loosening, you need to overcome the same friction (decreasing) but do
not have the stretching element of the material..

So in principle, if you tighten up new, greased nuts on a thread and
then immediately take them off using a torque wrench - it should take
less effort?
This just seems so obvious, i can see I'm going to have to have a go
to test the theory. ;-)

the friction is the problem, when tightening you have the mating surfaces
already sliding and it easier to keep them sliding than it is to re-start
them sliding, especially in the opposite direction, the metal itself acts a
bit like a one-way clutch.
How about this for an analogy: Imagine two pieces of spiky carpet (giant
size version of the faces of the nut and wheel) if you were to rotate and
compress the carpet then the fibres would all get squashed and interlock, to
undo in the opposite direction you have to overcome the bent fibres and get
them going the other way.

Ah ok, I was considering the fact that some low torque is used to get

the carpets closer togther , then bigger torque to lock. Sensibly the
same torque would then be needed to break the bond, and then a much
lower than low torque to continue as you are then just spinning the nut
rather than parting the objects.

This I found intersting:
http://www.hexagon.de/tasignat.htm

"In one release angle study, a part had a tightening angle of 120
degrees. Once the part sat overnight, the release angle was 20 degrees.
The vendor was already aware there was a major problem because the parts
were falling apart.
The study showed that relaxation in the threads was causing an
approximately 80% loss in clamp force over a 12 hour period. The release
angle method provided a quantitative answer as to how much clamp force
was being lost and clearly showed that there had to be a redesign of the
parts."

which must have a bearing on the original question.

#19

Chris Whelan expressed precisely :

Quote:

On Tue, 10 Nov 2009 18:06:00 +0000, Harry Bloomfield wrote:

Dave Plowman (News) used his keyboard to write :
BTW, congrats to Audi for giving the wheel bolt torque in the driver's
handbook. 120 Nm If only they took their own advice - it was nowhere
that tight when I took it off.

They can settle in a little, especially so on a new car. The advice is
to recheck them after a period.

By what process would a wheel bolt, tightened to the correct torque,
become significantly less tight?

Did I say significantly?

Check your cars handbook, most do recommend that the torque is
rechecked after a few miles. All/most car manuals also recommended that
cylinder head bolts are retorqued after 500/1000 miles it's all the
same process of settling in. The slightly high spots between the faces
settle in and the tightness declines.

--
Regards,
Harry (M1BYT) (L)
http://www.ukradioamateur.co.uk