Wheel nut engagement

[milliemarlin]

I have just read Scott’s “Berlinetta build and restoration” thread in which he mentions wisely changing his wheel studs to get a better thread engagement. This is a subject that is of interest to me as I work on my new car.

Stud length was one of the things checked on my cars SVA. The testers said that fitting alloy wheels quite often results in too little engagement. They used a Vernier calliper to measure the depth but I don’t know the minimum they expected. This web site has lots of thread info

http://roymechx.co.uk/Useful_Tables/Screws/Thread_tol.html

I have used this web site for other reasons but due to some kind of problem the site has moved so google can’t seem to find it. I am pleased to see that it is still available.

If I have a board moment I might do the calculations.

Meantime, I have read in quite a few places that 1.5 x diameter is a good estimate with a healthy safety factor. So for Millie’s Ford studs – 12mm 1.5 pitch a 1.5*12 = 18 mm nut length or 18/1.5pitch=12 turns.

That sounded a bit too long. So checked the original Ford Sierra wheel nuts and they are 15mm long. The Sierra has 4 studs. Surprisingly, the wheel nuts for the 5 stud Granada wheels are a massive 22mm long. So I would be interested to know if there is a definitive guide to the thread engagement.

I think Scott’s nuts are an imperial size. I believe his stud penetration is more than adequate (no tacky comments please).
Paul

[Alan c]

Re: Wheel nut engagement

Typical guideline is to have 1.5 threads above the top of a nut whatever application (as the first 1.5 threads are usually not fully formed due to how a thread is made - rolled or cut). If you have the right wheel nuts and studs this 1.5 should happen. More threads does not matter other than more threads to corrode, just wasted length or stick out and get in way. To get my wheel offsets I had to fit concentric spacers which made mine too short so I replaced them. No such luck as just a medium tap of the hammer - was more several heavy blows for me to get them out.

[stevejgreen]

Re: Wheel nut engagement

Standard mechanical engineering is to look for thread engagement that is indeed 1 1/2 times the tread diameter. This is usual when installing studs or threading a component part.
Standard mechanical engineering nuts however are only the diameter thick.
Somewhere between the two would be fine taking into account of the materials being used. Wheel nuts made of alloy will probably be of a softer material so greater thread engagement would be preferable.
Somewhere I have an engineering guide that compares different materials and torques that can be applied for a given thread engagement. I will try and look it out, but it's probably in the last box of books I will look in.

[Alan c]

Re: Wheel nut engagement

On the subject of bolt tips - if you have a bolt and nut in a vertical position have the bolt point downwards. If the nut drops off the bolt has a chance of staying in place and doing its job if its in shear. If you have it the other way nut off bolt drop out - no chance left. This assume no bolt access issues of course. I still see the odd photos of this not opportunity not taken.

[fouter]

Re: Wheel nut engagement

Hi folks,
Just incase anyone is still interested and not wanting to start arguments this is what I learned on a bolt torquing course(yes there are such things, where you have to be certified) that I did a few years ago.
Steve is quite correct 1.5 times the thread diameter for the minimum thread depth in at tapped hole.
Standard engineering nuts are only O.8 of the thickness.
The correct torque figures can get a bit technical dependent on the grade of the nuts and the coefficient of friction of any lubricant being used
( there are usually readily available for copper based and zinc based products) or if they are dry fitted so you have to be careful where you get torque figures.
The theory is that the threads on the stud are stretched elastically to apply a load on the nut that prevent it working loose. For normal nuts there should also be at least 2 full threads protruding from the nut.
Hope this is helpful.
Regards
Graham