Torque value-HELP

[Junkman]

I have painted the rotor face where the alloy wheel meets it on every car since I had the problem of salt causing corrosion between the rotor and the wheel. I have never had any problem getting the wheels off ever since and I have never had a wheel come off or even loosen when I used never seize on the studs. Before never seize, people would use axle grease to keep the nuts from rusting to the studs. Some might not agree with this practice, but for me it works and that is what counts. Everyone is free to make their own decision as to how they will proceed for the future. There is always room for dissent and if anyone thinks that this method is not safe, then I would tell them not to do it. We are all responsible for our own decissions.... The Junkman

 

[JD4610]

</font><font color="blue" class="small">( why the reduction in torque????? dry or lubricate threads... 100 ft pounds is still the same..... Is the 20% what the book says????? Doesn't make any sense to me..... )</font>

Yes, 100 lb/ft is still the same, but what is happening to the fastener is not the same.

It is important to remember how a bolt or stud works. They work by stretching just slightly, like a rubber band. As you tighten the lug nut, you are actually stretching the stud toward the outside of the wheel, and it is the stud's wanting to spring back to it's original length that actually holds the rim to the hub.

What's important, as we all know, is that the stud can only stretch so far before it becomes damaged, and will no longer have the strength to spring back. So, we need a way to measure how far the bolt is stretching, so we don't go too far. That's what the torque specifications are for. As we tighten the nut, the stud is stretched and the farther it is stretched the more pressure is placed on the threads between the stud and nut, and also beween the nut and the rim. This pressure results in increasing friction as the nut is tightened, and thus an increasing amount of torque is required to continue turning the nut.

Somewhere, an engineer decided that a certain amount of torque was required to stretch the stud enough to sufficiently hold the wheel to the hub. When you put grease or other lube on the stud, you have now reduced the friction between the stud and nut, therefore, the stud will have to be stretched further before friction increases enough to meet the torque value, possibly exceeding the mechanical limits of the stud.

The 20% value is a generally recognized value for anti-seize. If you want to be technical, many engineering books will give exact figures based on the exact lubricant, type/style of fastener, and thread class, among others.

I'm sure there was a heck of a lot easier way of saying this, but I haven't gotten much sleep lately /forums/images/graemlins/blush.gif