Having had a set of new tyres the other week. I've finally got around to looking at the paperwork.

The handbook for the car says the wheel nuts should be tightened to 105Nm. I notice they've written that they've set them to 120Nm.

Should I care? Is this significant?

Hi
It just means that they are slightly over tightened. I wouldnt worry about it, personally I dont think it makes a difference.

Glenn

Ah, thanks for the fast reply.

Being an ignoramus I didn't know whether the scale was linear, in which case as you say, no great thing, or logarithmic, in which case abandon hope as the car is about to shatter into a million pieces.

Mind is officially at rest.

N = Newton, which is the SI unit of force
m = metre, which is the SI unit of length

If you apply a force of 1 Newton at a distance of 1 metre then the torque applied is 1 Newton metre or 1Nm

You can increase the torque applied by increasing the force applied, or by increasing the distance at which the force is applied i.e. using a longer lever.

The difference that you describe is significant and since they have written down the value it clearly wasn't accidental. (Modern torque spanners claim accuracies around plus or minus one percent). So I would at least ask why they did it - there may be new guidance from the manufacturer, but if it is some individual saying 105 is good so 120 must be better then some education is required.

Torque loading is calculated carefully to give enough material distortion to lock the thread without going past the elastic limit. At the very least, an increase over spec. will make it more difficult for you to undo the wheelnuts if you need to remove a wheel at the roadside.

Dipstick, I have just worked out that the torque of 120 newton meters on the offside lower front wheel nut is in fact the exact amount of longitudinal force required to break the woopy camflange which you will find on the king lead which connects to the phopho valve, to recitify this problem you have to drive backwards, heading east arond the world to unwind the transitional forces applied to the said cylindrical retaining device....

I hope this is not too technical for you...

And by the way talking about Lin's ear and fire place articles is just showing off.....

Pete LOL

Is this connected to the torque convertor in that I put fuel in the petrol tank and get many newton metres at the road wheels?

...or the 'Talk' convertor , aka Lexus car club posting site?

Would have an ebay 'Fuel Saver@ magnet thing in the fuel tank effect the wheel nuts
Tightened Torque as the wheels rotate making the nuts closer and then further away ?

Oh nuts.

Ok, as I'm going to get them to swap my tyres about anyway I'll get it sorted, or indeed enpurchasulate a torque wrench myself so I can be sure it's right everywhere forever.

Pete, you described my usual way of getting anywhere after Mrs Dipstick has been at the satnav, so looks like I'm ok there.

Thank you boys. Oh, and I'll tell you what - wasabi covered peanuts are a joy to savour. I like to bring you new experiences.

...but, like Olives tasting better somehow in Andalucia, wasabi peanuts taste at their best looking at moonlit bamboo grove in Kyoto? (I was there this time last year!)

I like a Cashew or a Pecan myself

Well that's as maybe, but I've also discovered that wasabi coating makes terrible white stains on your cashmere.

Which isn't a phrase you type every day, and how I'm going to explain THIS in my meeting later I have no idea.

It's not a tool that most owners would use very often. I wouldn't bother personally. It is difficult for the average person to overtighten a wheelnut by hand, using the tool provided with the car. If you have to change a wheel then you are likely to be going to a garage shortly after and they can check the torque for you.

Unfortunately there are still tyre-fitters around who don't understand the importance of the correct torque and it makes me cringe when I see wheelnuts being tightened with a powered impact wrench, but a good fitter should get it right and should set the final torque with a hand tool.

If you are determined to buy one, you can get a decent "pre-set" mechanical device for about £25. Don't buy a cheap one that cannot be calibrated, they are worse than useless.

Few people have a good feel for Newton Metres. Funnily enough, one Newton is about the force exerted by a medium sized apple under normal gravity. Personally, I am old enough to prefer ft-lb and if I translate your original figures, you would have to apply a force of about 78 lb on the end of a 12 inch spanner to get a torque of 105 Nm. To get that up to 120 Nm the force on the end of the same spanner would have to be about 89 lb.

Undoing the nut always requires more force than was used to tighten it, as many have discovered to their cost when faced with roadside wheel removal. The wheel-nut spanner supplied with my car is only about 10 inches long, so I always carry a length of steel tube that fits over it snugly and makes it easier for me to undo the nuts if I need to.

I would be interested to know what reason you are given for them setting the torque so far above the manufacturer's recommendation?

Good luck.

Thanks for that useful advice Sagitar - noted and appreciated.

As to their reason - "it says that in our book so that's what we've done". Whatever that means.

I'm not over worried about it and will get it sorted by them next week. As to the torque wrench, for £25 or so it's worth it I think - I'm a real hypochondriac when it comes to cars! Every tiny noise and I think it's going to be twins.

I'll still be obsessing about it in three cars time I expect, so might as well. I'll look on the 'bay for summat.