There is something that bogs my mind lol
The question is how on earth a car that is about 1.9 tons wheel torque values are same as 1.3 tons car ?

Let me clear on this :

Cadillac Fleetwood Brougham 1.9 tons , 140 Nm wheel torque

Chevrolet Cruze 1.3 tons , 140 Nm

Jaguar XJ 1.8 tons , 160 Nm

Jaguar being slightly lighter than Cadillac gets more torque value to the owners manual

I haven't got any idea why it is like that
lol

 

Regent, the torque on a wheel stud is a combination of factors. First off, is the wheel "hub centric" or not, ie, does the rim rest on the hub or do the studs hold the rim still. If the studs have to hold the rim in place, then the studs see more loading and therefore can not be torqued as tight so that the stud does not exceed the maximum allowable stress. Also, there is some affect from the size and material that the stud is made up of. The larger the stud, the more torque it can handle safely. Like wise, if the stud is made out of better material, it can handle more torque. Obviously, the Jag is meant to do higher speed turns than the Caddy. Therefore the Jag will see higher stresses that need to be overcome.

Also, the torque is there to hold the wheel tightly against the hub. When you make a high speed turn, the forces attempt to rip the wheel away from the hub. So, the torque is needed to hold the rim tight against the hub. You don't get enough torque, the stud stretches and now the rim can become loose (you can imagine where that will lead). If you torque it too much, you can exceed the maximum allowable stress for the stud and then the studs sheer and that is really not good. Hence why there is a range that is acceptable for torquing things.

Please keep in mind that all metals stretch some and when they stretch, they become stronger (to a point). When you torque a bolt, you want to put a slight amount of stretch into the fasteners to improve their strength and reach a point where the loads are not going to cause the fasteners to stretch any more. Now, we are talking on the scale of thousandths of an inch, if not smaller. So, it is not like you are going to visually see it. There is a method of torquing where you actually measure the unstressed length of a bolt and then through a calculation, you can figure out the torque applied by finding the torqued length. But, that is way more difficult than is needed. This is normally used when you torque things into the millions of foot pounds (yes, I have to deal with things like this periodically). But then, we are torquing things using heat. So, it makes the whole thing very fun to do.

You want to know anything about torque and the related subject, let me know. I have received training in this and will teach you what you want/need to know.

 

Kudos to Thermo.

Another way to state it is that required torque is a function of lug nut/bolt size, number of bolts and the dynamic force (weight&speed) applied to each bolt.

KBO mate

 

Regent,

I'm curious about your source/application for the XJ? Is that X350? or later? Or maybe something pre-dating X300? Just shocked at the magnitude of the difference:

I've got 88-102 N-m for the X300 wheel torques from the CD that came with the car.

JTIS for the S-Types gives me 128 N-m. If a range, I didn't bother emailing the bottom of it to myself - reading off phone, currently...

 

Thanks Thermo , this is really very quenching and clinching answer , I am very satisfied
aholbro , it's 1993 Jaguar XJ6 but as Thermo said there were many things that affect wheel torque specs rather than car's weight itself

 

My Holden Sportwagon manual states 170Nm for the wheel nuts.
If I ever need to change a wheel on the road I'll need a 3ft extension bar.

 

I torque the bolts either my arm's power or torque wrench . Recently , I had to replace 3 rear wheel studs in my Jag due to stupid tyre shop staff's over tightening the bolts . They do use nothing but power tools to tighten the bolts and hence when you need to tighten them to the specs according to the manual results are dissatisfied . I tried my Dewalt to get them to loose and even that machine got very hot .
There is another thing I wanna ask, do we have to hear the clacking noise when tightening the bolts ?
Why I am asking is this because I was able to loose the bolts in Cruze w/o any effort or requiring power tools and I looked at it's manual it stated 140Nm value .So they gave quickly when the wheels fitted they do use this value 140Nm

This time I picked up front wheel in Cruze ,bear in mind factory torqued, I noticed that there were a few swings left to be tightened to hear the clacking noise .
I said that was enough then there is no need to use power tools to tighten the bolts but what I wanna know if there is a necessity to hear a cracking or clacking noise from bolts

 

120Nm or 90lb.ft in my S type handbook.

 

What's the torque setting for wheel lugs on an 08 XK?

Tom

 

page 282 of 2007 XK Owner's Handbook states 125Nm/92 Ib ft.........

Adrian, 2000 XK8 Conv. & 2007 XK Coupe

 

Thanks, guess I should have checked the Owners Manual first.

Cheers

Tom