single nut locking torque

[firstboaz]

As of this year we're using 10 inch wheels (Keizer CL10) with single locking nut.
We tried to calculate the needed locking torque that we need. We got approx. 160 Nm in the calculations.
We used 180 Nm for safety factor.
When we drive the car the single nut gets loose after around 20 minutes of driving.
We tried to calculate again and again, still we got the same results.
Is someone familiar with single lock nuts and willing to help us?
If you use single lock nuts what is your locking torque?

Thanks for the help,

Boaz Cohen
Head of power delivery team
BGRacing
Ben Gurion University
Israel

[BillCobb]

Maybe its not a nut problem but a hub, stud or bearing problem.

[Claude Rouelle]

You cannot look at the locking torque only. You need to "translate" that in pressure on the rim. What is the resulting axial force coming from the wheel torque To do that you need to take into account the pitch of the thread. A fine thread will have a different effect that a gross thread.

The other issue is that you may need left hand or right hand thread depending the side of the car you are looking at. I let you guess why. You also need to look at the driving or braking torques that are not necessarily the same.

[DougMilliken]

Is someone familiar with single lock nuts and willing to help us?
There is a long thread (sorry for pun) on this topic --
http://www.fsae.com/forums/showthread.php?9943-center-lock-hubs-and-wheels/page9
This link is in the middle of the discussion, where I think it gets interesting...but you may want to start at the beginning.

There are probably other threads too, but this is the first good one my searching turned up.

[maxhouck]

We had the same issue until we started using anti-seize on the threads. Use plenty of antiseize on the splines (if applicable), spindle, and the threads of the nut.

[Buckingham]

We had the same issue until we started using anti-seize on the threads. Use plenty of antiseize on the splines (if applicable), spindle, and the threads of the nut.

Wet Torque and Dry Torque are two different specifications. 180 NM WET will put substantially higher axial load on the threads than 180 DRY. If you aren't knowledgeable on this concept, you might one day wonder "why it broke".

[caantoun]

Lets start with this: What is the goal of this nut?
Is it to apply a torque? Or to apply a clamp load?
I would argue it is the latter, in which case, installation torque is not actually the most accurate measure. IF you get the nut to fully snugged down (no play in joint) and then turn it a specified angle, using the stiffness of your bolt, wheel and hub as springs in series, you can calculate the clamping force applied by the nut. If you can figure out the underhead friction coefficient as well, then you can use this clamp load to also determine your prevailing torque for locking.
I hope this is helpful. If you have further questions about bolted joint systems, feel free to ask.

[Drew Price]

Aren't center lock wheel nuts required to have a locking feature as well?

^^caantoun is on the right track. There are lookup tables in places like Machinery's Handbook and online that can help you figure out clamping load vs. tightening torque for various thread pitches as well, I wouldn't try to calculate it from first principles.

[JSR]

Aren't center lock wheel nuts required to have a locking feature as well?

T6.3.2 Any wheel mounting system that uses a single retaining nut must incorporate a device to retain the nut
and the wheel in the event that the nut loosens. A second nut (“jam nut”) does not meet these requirements.

[caantoun]

Drew,
I agree, a lookup table is likely a good place to start, although with the thread pitch and joint stiffness it actually isnt that tough a cookie to crack. For a first hack at it though, tables all the way!
If you really want to knock the judges socks off though, have some test data quantifying the nut factor of the joint and the joint tension vs. joint angle. These are tests OEM's run for every single joint on the car.
This is likely a bit much, but is something worth thinking about. Always good to know how much work you *could* put into something. But its even better to know how much work you *need* to put into it.
If you only need a +/-15% estimation, you'd be right to stop with a table estimation and some simple validation work.

[BillCobb]

O.E.M.s have specifications on fasteners such as this to be followed to the letter by the nut runner guns used on assembly lines (robotic as well as human operators. Specs are for flat counts and something called 'prevailing torque'. Even though the nut runner traveled so many flats, the last torque reading must be within an acceptable range. Likewise, a gun reaching a final torque level must have acumulated so many flats. This addresses misthreaded nuts and studs as well as missing parts (as in: you ran a wheel stud but the wheel is not in correct position). Don't laugh, it's happened. For example if the paint line throws down the wrong color or type of wheel, the build manifest will put a hold on the chassis line. But if that line had started, there will be no wheel. So, to make sure all 4 wheels are correct, you check the torque (wheel is there, and the flats, wheel is there and not misthreaded). Sure, none of you folks would ever build a FSAE car and forget to put a wheel on, but when you make a thousand per day, shit happens.

And, you seem to be having trouble KEEPING A WHEEL ON ???)