Read this thread: http://www.subaruoutback.org/forums/66-problems-maintenance/25711-breaking-wheel-studs.html

Turns out in his case it was a warped rotor

 

wheel stud keep breaking

I'm having the same problem on my 2005 subaru outback limited sedan. I've changed rotors, many wheel studs, the only thing I haven't done is change the rims but had them checked and are not worped or bent. I tourqe them to 70ft lbs by hand every time i rotate or change tires, i think there is a defect or subaru needs to call for a recall:28:

 

:. . . I tourqe them to 70ft lbs by hand every time i rotate or change tires, . . .

This appeared in the November 2007 Subaru TechTips:

When was the last time you checked to see how tight you are making your customer’s lug nuts when servicing their Subaru? Wheel lug torque specifications have significantly changed over time. Here are some examples:
2000MY Outback: 65 +/-7 ft-lb
2001~04MY Outback: 65 ft-lb (with no tolerance)
2005~06MY Outback: 81.1 ft-lb
2007MY Outback: 88.5 ft-lb
2007MY Tribeca (Non-Chrome): 88.5 ft-lb
2007MY Tribeca (Chrome): 110.6 ft-lb
2007MY Impreza: 73.8 ft-lb
2007MY Forester: 73.8 ft-lb
This list is in no way a comprehensive one, however, it clearly illustrates how much things have and will continue to change. So, the next time you are putting the wheels on a customer’s car, don’t assume you know the proper torque for the lug nuts if you haven’t checked the applicable Service Manual.

Incidentally, in my 2007 Owners Manual, the wheel lug nut torque spec is found in the "In case of emergency" chapter, in the section on replacing a flat tire. It isn't highlighted in any way, but it reads: "The torque for tightening the nuts is 74 to 89 lbf·ft (100 to 120 N·m, 10 to 12 kgf·m)." I would imagine that the spec is also provided in Owners Manuals for other years.

 

I haven't run into broken studs except in the case where someone cross threaded the nuts or they were left loose too long and the stress snapped them.

I have come across a lot of Subaru lug nuts that after several times off/on, the threads in the nuts themselves have stretched making it difficult to torque them to stay torqued. My 99 never broke any bolts, but the first time I noticed it, over a 2 week period, I would feel the looseness and check the lug nuts, having to torque them again. I got a new set for all the wheels and problem solved.

So, I rotate my tires every 10k, and brakes are done every 60k or so with exception of the flush, and every 2 years a new set of lug nuts goes on the cars. New lug nuts is one of the new year chores I do. Cost is about $3 each, but when you factor in the added cost of replacing bolts or repairing damage caused by a loose wheel or one that comes off, its worth it.

 

subarus break wheel studs much more frequently than any other cars in my experience. buy new studs and put anti-seize compound on the threads.

 

I've never had any problems with my lug nuts on both of my subarus, I rotate my rims every 10,000 miles and torque the lug nuts to 90ft/pounds with a torque wrench in the star pattern for 5 bolt hubs. Maybe its uneven torque on the lug nuts or lack of torque that causes these failures?

 

My '05 hasn't been an issue.
I do have a set of winter wheels that have their own lug nuts, so, even though twice a year I change tires (summer, winter), I never have a lug nut or stud problem.

I rotate the tires only when I change from summer to winter and back again (which would average about 15,000 miles between changes).

More importantly, though, ever since I began driving, I always keep an eye on how the tire tread is wearing and adjust the pressures accordingly. Right now I am running 27 psi in the front and 24 in the rear, as the centers of the tires were wearing faster than the outer edges. I find the lower pressure gives for a better ride, handling is still the same as if I have 33/30 psi.

My truck which has 10 ply truck radials on it can take up to 80 psi. I typically run between 45 and 50 psi all around which makes the tires wear nearly perfectly! I don't carry a heavy load very often. If I do, I will add air if I have to go more than about 10 miles. Once the load is delivered, the pressures will be brought back down to 45-50.

The only times I get any abnormal tire wear is if I have lost wheel weights and/or if the vehicle needs an alignment.