My son has an F150 that has a history of breaking wheel studs. First, some background. It is a 2000 4WD we bought when it had 187000 miles in July of 2016. He is running 20" slightly aggressive mud tires with 1 1/2" spacers and a 6" rough country lift. When we got the truck it had stock wheels and tires and the front end was about wore out so we replaced all front end components, ball joints, tie rod ends, pitman arm, idler arm and wound up replacing both wheel hubs. This is one from 2000 that has 12mm studs, that year could be 12 or 14. We also rebuilt the 5.4 Triton which is irrelevent. During that time he had several studs to break. We didn't properly torque to begin with but we have since torqued all lug nuts to 100 ft/lb every time. The spacer nuts are at 150 ft/lb as determined by the machine shop that made the spacers. They are hub centric spacers so there should not be much more stress on the studs. We've never had a spacer stud to break, it's always the truck studs and it's usually been the front end moreso than the rear. Also, we did have studs to break prior to installing the aftermarket wheels and spacers and bigger tires. We thought we had it resolved by torqueing them til yesterday when he felt the front end begin to bounce. We wound up replacing 3 on one side then. We checked the other side tonight and one of them was broken. Tonight we took everything back off and applied some blue loctite to the truck studs and retorqued everything. We've tried 2 different torque wrenches and both seem to be the same. What else could be causing this? Everytime it happens the studs break right at the bottom of the wheel even with the inside end of the nut and the nuts screw right off by hand with no damage to the threads.

 

The stock stud torque is speced at 150 lb/ft. Reference page 219 of an Owner manual.
You fell prey to an unenginerred setup.
What is the metal and grade used for the spacers?
What is the stud Grade used for the spacer to the wheel?
What is the wheel offset in addition to the spacer thickness.
The total off set applies more leverage to the studs, the spacer and the front spindle rim.
The front spindle rim is really not very heavy.
Matter of fact if torqued too tight they will distort.
We can't engineer it for you but these are the things your dealing with.
I would be looking at a vendor product that is known to be strong enough for your application.
Good luck.

 

spacers are made for show cars with fancy wheels. They should NEVER be used on a 4 x 4 truck with a lift kit and off road use....... I think Bluegrass pointed out several BAD items that lead to this failure.. I don't think you can pinpoint ONE thing, you have several problems with this design.

 

It really depends on how much spacing is used. On my RX7, I've been running FD RX7 wheels and 225/50/R16 tires for years with 20mm hubcentric spacers. Given the offset difference between FC and FD, the center of the wheel is quite close to stock with this arrangement, minimizing lateral load on the hub's studs.

However, the setup in question has nearly double the spacer that I do. This exerts much more leverage on the truck's studs, and it is magnified by larger/heavier wheels/tires. It is also the same 5x114.3 pattern as a Mustang/RX7/etc

My advice would be to go down to 3/4"/20mm spacers in order to put the wheels' centerline closer to stock. If need be, change to a wheel with less backspacing too.