Kwik-fit and a puncture.
in [Car Maintenance]
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From: Chris Whelan on 10 Nov 2009 14:06 On Tue, 10 Nov 2009 18:54:42 +0000, Conor wrote: > In article <ZsiKm.17$uh1.10(a)newsfe20.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.
From: prb on 10 Nov 2009 14:26 In article <hdccgi$5er$1(a)news.albasani.net>, roger20nospam(a)ntlworld.com says... > > "Chris Whelan" <cawhelan(a)prejudicentlworld.com> wrote in message > news:ZsiKm.17$uh1.10(a)newsfe20.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?
From: Paul on 10 Nov 2009 14:29 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....
From: Mrcheerful on 10 Nov 2009 14:35 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.
From: Paul on 10 Nov 2009 14:42
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. ;-) |