Mech33

Unfortunately the 3/8" adapter still won't let you use a breaker bar to apply 443 ft*lbs without snapping it...

mqandil

You are very welcome. Have a safe trip.

I believe the wheel nut is made from forged Aluminum, which has 64,000 psi yield strength which was the basis for my calculations.
Yes I would run it up to the stop mark, to make sure you exceed the specified torque. It is safer to be slightly over than being under torqued.

Indeed yes you do still need a small torque wrench capable of achieving 75 ft.lbs. A typical emergency, you get a flat while away from home and need to get it repaired at the nearest tire shop. Most tire shops have small or medium size torque wenches that are rated up to 250 ft.lbs but usually they don't carry larger sizes, which forces you to seek a Porsche service to perform the repair. Once the wheel off the car, any reputable tire shop can repair, mount & balance your tire, but without the correct torque wrench they won't take the risk to reattach your wheel to the car. In my case I normally carry a small torque wrench which is only 11" long, and I tuck it under passenger seat, along a 3/4" to 1/2" & 3/8" & 1/4" adaptors which allows me to use the small torque wrench to achieve the initial threshold torque. I also carry a collapsible breaker bar & jack pad jacking point tool adaptor. This allows me to take my wheel off and on at any time, just in case it is a bad flat and I can't drive the car to the nearest tire shop and must remove my wheel off and take it to the tire shop. These tools are small enough to tuck under or behind the seat or in trunk without losing much space rather than carrying my big guns (tools) with me at all times. Mark

mqandil

You can use the 3/8" or 1/4" adopter to use with the small torque wrench to apply the initial 74 ft.lb torque, but you absloutly right you can't use to apply the full 443 ft.lb torque and must use a minimum of 1/2" & preferably 3/4" for the breaker bar to loosen or tighten the nut. Mark

Loess

Yes I'd use the small adaptor to apply the initial torque. I think you could find a small torque wrench and 1/2" or 3/4" breaker bar in an emergency however finding a 3/4" torque wrench may be more difficult.

Wouldn't the yield strength likely be based on tension? The conversion from torque to compression on the nut would be complex and the failure would more related to the compressive strength or shear strength and cross sectional area of the nut would it not?

gled

Thanks Mark for the double check, I know I'm not alone. I met you at Sunset when you had your MPSS tires mounted. I'm in Hillsboro. Gordon

mqandil

The yield strength is a purely physical property of the material. Most failures of bolted assemblies are a result of loosing of initial preload rather than tensile failure of bolt as a result of higher preload or sheer of thread or bolt as a result of an over torque providing the material is not defective or corroded.
The estimated stresses for a given preload are fairly easy to predict or calculate if no grease or anti-seize materials are used on the threads. All you need to know to calculate the tensile or compresive stresses, is type of the materials used, the physical diameter of the bolt & nut, and seating dimensions including the thread details such as pitch, etc which can be easily attained by physical measurement of the bolt & nut, and finally the coefficient of friction of the threads and seating area which is what really complicates the estimation due to the presence of grease or anti-seize compound plus few other factors, but an engineer can usually make some safe assumptions about the coefficient of friction based on experience and is able to get a rough estimate of the stresses for a given torque value, while understanding the results can vary by as much as (plus or minus) 15% error in the estimate as a result of his or her assumption of the coefficient of friction. So when an engineer estimates that you can torque the bolt safely to 1000 ft.lbs without causing permenant damage to the bolt, nut or wheel, you can safely attest that torquing the wheel to 600 ft.lbs which is so much lower than the estimate, should not cause any permanent damage to these component. That's all what I was trying to say, and that the additional 100 ft.lbs over-torquing or even 150 ft.lbs as a result of using the Porsche emergency procedure should not be of any concern to us, and There is no need to change anyone plans to find the correct size torque wrench to re torque the wheel to the correct lower specified value. Personally I feel safe to drive & track my car indefinitely with the higher torque value after performing the Porsche emergency procedure. Mark

mqandil

Hi Gordon. I remember you and you are very welcome. It was really nice meeting you.
Are you coming today or tomorrow to PIR. There are several events taking place this weekend. Mark

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