Nick is an engineer from Minneapolis-St. Paul. He came to me with a simple question this week. His buddy just bought a new Subaru. They’re famous for breaking wheel studs—an incredibly frustrating problem. Eager to avoid time-consuming repairs down the line, Nick asked what he could do to prevent the issue.
Around these parts, we love posing questions for Autopian Asks. When Nick reached out to me with his question, though, I realized we’ve never done Autopian Answers before. I figured I’d answer his query as best I could, and let you all chime in with your own knowledge, too.
So, what is to be done? Let’s explore how to best avoid wheel stud failure in a modern Subaru.
@rainbowdefault.bsky.social a buddy just bought a new Subaru and I’d like him to be able to service the wheels without the studs snapping. Is there anything you can do to prevent it? A certain grease or torquing to the right level?
— Nick S (@nottooserious.bsky.social) December 12, 2024 at 2:44 PM
Make It (Not) Snappy
Let’s start with a basic definition of the issue. The wheel stud is the threaded steel part on which you tighten the wheel nuts. On most cars, these are lifetime items that never need replacing. However, Subaru has gained a reputation in recent years for weak wheel studs that snap relatively easily. Our own Matt Hardigree had this experience with his not-too-old Forester and he wasn’t alone.
Head over to the forums and you’ll find all kinds of complaints. “Yeah, those stock Subaru studs are about as strong as pretzel sticks,” says one owner. There are plenty of others out there telling similar stories.
They can be a pain to replace, too. You need to remove the wheel, brake caliper, and rotor to get at the studs, then you need to deliver many good whacks from a sledgehammer to get the damaged part out. This can be easy or excruciating depending on how seized they are. Finally, you need to wiggle the new stud into place and use a stud installing tool (or stack of washers) to press fit it into the hub. This is easier said then done at times—I’ve had to do this job on a Honda Civic, and it wasn’t much fun..
Nick says his friend’s car is brand new, so you would normally expect the studs to last a good couple decades. However, Subaru’s wheel studs have a particularly poor reputation. Is there something especially bad about them?
As it turns out, the experts over at Art’s Automotive have looked into the problem. The Bay Area shop specializes in Japanese automobiles, and found a high number of Subaru studs were failing in the field.
It’s far from the worst job, but it can really put a crimp in your weekend if you’re regularly driving in the Snow Belt.
Their article covers what makes Subaru wheel studs different, and proposes a theory as to their common failure. Unlike other Japanese brands, Subaru’s wheel nuts use an M12 x 1.25 mm thread, rather than the more common M12 x 1.5 mm thread. The second number—1.25 mm—refers to the thread pitch. Basically, the threads are more closely packed on the Subaru studs. If you measure from the peak of one thread to the next, you’d get 1.25 mm (0.049 inch) on a Subaru wheel stud. Nissan uses the same pitch too, but for some reason, weak studs appear to be more of a Subaru issue.
All in all, for two studs of the same nominal diameter, the one with finer-pitch threads is usually stronger in terms of tensile strength. That’s because a larger thread pitch also creates a deeper cut, which reduces the amount of metal able to take load. You’d thus expect Subaru’s fine-pitch studs to be stronger, not weaker, and more resistant to overeager mechanics with impact guns, too. And yet!
The thing is, finer-pitch threads do come with drawbacks, too, as noted by Art’s Automotive. They’re more likely to suffer galling, where small bits of metal shear off the threads and create little balls that can jam everything up. They’re also easier to damage, easier to cross-thread, and more likely to seize due to excess friction during high-speed tightening. There’s the smoking gun—while the finer-pitch threads make for technically-stronger studs, they also make for studs that are more likely to fail when using impact guns or during careless assembly. Of course, it could also be that Subaru just uses cheap lug studs made out of crappy materials, but that’s harder to investigate without a university-spec laboratory on hand.
The Solution
So what is to be done? Well, Art’s Automotive has a simple solution. They suggest using anti-seize or a touch of grease on lug nuts, in order to reduce friction. This should prevent seizing or galling, which is often a precursor to snapping a lug nut. Lug nuts are supposed to be installed dry, but this should be perfectly safe as long as you keep torque to the right spec. Technically, lubricant on the threads increases the total tensile load felt by the stud when tightening to a given torque, but as long as you’re sticking to the proper torque spec, you’re unlikely to hit any issues. Avoiding mechanics or tire shops that don’t use their impact tools safely is key, too.
John Cadogan explains how to safely choose the right torque spec when using anti-seize on your lug nuts.Â
Installing the lug nuts more slowly is also a good habit to get into. Our grandmammies and grandpappies couldn’t be doing with all this electric nonsense. They used good old-fashioned tire irons and took their time doing so.
Beyond that, you can always go the upgrade path. ARP makes studs that are well-regarded for their extra strength. I wouldn’t bother pre-emptively ripping out all the studs and changing them, though. Don’t make work for yourself! If you’re doing a brake or wheel bearing service down the line though, that might be a good time to change over.
In any case, if you do snap a stud, you won’t be the first Subaru owner to do so. You’ll get knowing nods from others at the parts store when you go in to pick up replacements. I hope this puts you at ease and helps your buddy have many carefree years of motoring in their Subaru. Not everyone does, of course, but we should always hope for the best!
Images: Subaru, via Youtube Screenshot
Adding lubricant will reduce friction and thus make the lug nut see less resistance. So when you tighten to the torque specification you will increase the tensile preload. It is the same effect as overtorqing a dry nut
To avoid:
Turn the old milwaukeeni up to eleven, don’t even start the nut by hand, just feel it though the sloppy anvil to deep (chrome) socket to nut to stud connection, and give er all the way.
But in all seriousness, my wife and I have owned about 15 sacked out Subarus over the last 12 years or so. The newest has been a 3rd generation outback. And even with all the advancements and safety, I’d probably prefer to not own anything newer than a 2004. Anyway, I can count on one hand how many wheel studs I’ve had to replace on my personal vehicles over the years. The replacement was most often in short order after purchasing a brand used Subaru from whoever/wherever.
However, in the day to day at the local independent shop, I run into a handful a month. Pretty easy to discern when it’s going to happen. Just a little tight is a good sign of things to come. But… sometimes, they just ruin your day right off the rip and you struggle removing one stubborn, mopped out nut on a stripped out stud while not damaging some generic aluminum wheel that costs 500 bucks or more (new) for no apparent reason. To be fair though, I see all the brands have bunged up wheel studs. Although Subaru is definitely more frequent.
What I really despise though, is the GM, Chrysler, Ford swole lug nuts. Not sure what it’s like elsewhere, but in the rust belt, they are a real treat. 18.5, 19.5, 21.5, and 22.5 sockets are always at the ready. And sometimes, a full size up is required. Or SAE. Or BFH. Can’t recall when I last had to up size a socket just to fit a Subaru lug nut.
Why don’t you use studs with buil in nuts? Must be a US thing. Never had one shredded in 20+ years over a variety of cars
I find those 10x harder to install a wheel, as you have to get the wheel lined up before threading the stud in.
With lugs like this, you just slap the wheel on and thread the nuts on as slowly as you like.
My understanding is that the use of studs is a predominantly European thing, whilst most other countries use separate lugs/nuts.
The problem of snapping studs seems to be a Subaru-specific thing, and is not caused by the use of a separate lug/nut.
Anecdotally, I’ve never had an issue with the studs on any of my 5 cars that have this design.
First time I went to rotate the tires on my BRZ (bought 17k, probably around 22k when I rotated) it already had a cross threaded lug nut that snapped a stud off. I just do my lug nuts by hand off and on, hasn’t been an issue with that since. But I was real nervous when I took it in for new tires but I checked em all after and seems like ol discount tire didn’t damage any of em. The Nissans don’t have the same reported issues with snapping bolts cause Altima guy will happily swing through traffic at 90 with just two unbroken studs holding on the donut spare.
Or, before agreeing to buy one, make the dealer replace them. Bring four sets, make them put them on, watch them do it, THEN agree to purchase the car.
Just knowing this about the studs makes me not want to buy a Subaru, ever. Complete disregard for the simple things that should NEVER break. The solution exists and they ignore it.
By not being an idiot.
I’ve never snapped a wheel stud on 7 different Subarus: 02 WRX wagon, 04 STi, 05 STi, 2010 Outback, 2012 Impreza, 2020 Ascent, 2021 Ascent.
This.
Use an impact gun to remove lug nuts, not tighten them. That’s why we have torque wrenches. Broken studs usually indicate a desire to do a job easier instead of correctly.
Use an oxy-acetylene torch. Can’t snap if it’s liquid.
What was the question, again?
I’ve bagged on Subaru in a couple previous articles, especially commenting on the woeful tales of the Forester by Matt Hardigree. After more reading about the snapped studs I wonder how much of really is user/technician induced? I’ve done a little more reading and watching about the TR580 CVT in the current gen of Subarus. It seem like they have dialed that transmission into being a reliable unit. As long as you follow Subaru of Japan & Canada recommendation to change the trans fluid every 30k miles. I wonder why Subaru of America doesn’t make the same recommendation and instead call it ‘lifetime fluid’?
It’s worth reading this reddit thread. Sub Japan does not recommend CVT fluid changes every 30k. Just an inspection – just like in the USA. As the poster notes, the most common TR580 failure is an solenoid electronics failure which is unrelated to CVT fluid.
I have learned that the easiest way to get a flaming war going on an automotive forum is to promote anti-seize on wheel studs/bolts. I do this with no consequences and do all my own wheel off work except for tire installation. Even there I will just drop off the out-of-season wheels loose for new boots. The keyboard set insist that all four wheels will fall off simultaneously and that my family and I will die in a flaming wreck. I do not reduce the torque. With studs, you don’t want the exposed threads to rust. With bolts there are a couple of exposed threads behind the wheel flange, so same here. Whenever my cars go for a wheel off service I always loosen and re-tighten the bolts/nuts to proper torque. Sometimes I need to use a breaker bar to get them loose. This never happens if I have tightened them myself with a torque wrench. I once encountered a carful of young people headed for a wedding with a flat tire attempting to change it. Yep, the pitiful trunk wrench wouldn’t touch the lug nuts.
I do the labor on my wife’s 2018 Legacy and only recently have I had to snap 1 stud due to cross threading it apparently. That’s 1 total from 2018 till now. My secret is just using hand tools just torquing down to 90 ft/lbs. The only place I use anti-seize is around the hub so the wheel doesn’t stick to the lip. I rotate the tires every oil change which is every 5000 miles so they have been off plenty of times.
+1 for bluesky over the other thing
Thanks everyone, I was the one who posed the question on Bluesky. Lewin thanks for digging into the thread pitch, I think that’s indirectly the likely issue. I’m guessing with more threads per mm there’s significantly more surface area to gall. It’s also possible that the plating on the fasteners is just spec’ed poorly or cheaply or the manufacturer goes thinner on theirs. I also agree with the discussion that the smaller threads will likely be impacted by debris more easily. So what should my buddy do? Well he’s not mechanical, so he can’t carefully take the nuts off and clean studs and carefully re-torque each time, it’ll likely go to the corner mechanic. I’ll find a non-snowy, warm weekend in Minneapolis in December (lol) and help him put anti-seize on the studs. I agree with Lewin that the studs can absolutely take more tensile load.
Ya know its funny, my tracker (suzuki) uses the same goofy thread as subaru (1.25), and I’ve never actually broken one. However, the threads are constantly getting screwed up on them. I bought thread files and use a bit of anti-seize on my lugnuts to help mitigate the problem. And proper torquing of course.
Cross threading, filthy conditions, and gorillas with impact guns. I’ve put well over 600k miles over 4 Subarus driving in New England with lots of wheel removals and never broke a stud and we’re talking very abusive driving for 3 of those. I use a gun to get them off, check for debris, thread the nuts on until they’re seated in the wheel cup, give them a quick squeeze with the gun until it just starts to hammer, which usually gets me to around 60 ft/lbs, then torque by hand.
i’ve had nuts get stuck and I had to snap the studs to fix this all because some newb idiot at a tire shop decided to overtorque my lugnuts like crazy. i’ve personally never had that issue with shops that twist on by hand and then use a manual torque wrench the sobs when mounted. nowadays, if I see some idiot using just the air tool I tell them to stop and I bring out my own torque wrench.
I’m surprised that nobody has done a basic metallurgical composition and hardness comparison of these with the competition.
I mean, if you’re not working in an industry or university lab, you’re not gonna have the equipment.
As you say though, you’d think maybe there’s a Blackstone Labs of the fastener world that could touch on this for us. ARP, even?
At least, Torque Test channel on YT should do a comparison of tensile and shear strength of Suby vs. all other studs.
“you’d think maybe there’s a Blackstone Labs of the fastener world”
There is:
https://www.eag.com/about/locations/north-america/los-angeles-ca/
They should test the oil drain plugs too. My STI and BRZ had the softest metal on the drain plugs I’ve ever encountered.
I’m not stating Subaru did a good job, but a good bolted joint design will result in the male thread failing first (aka the drain plug). It’s easy to get a new bolt/drain plug, it’s a nightmare if you strip the female threads in the cast aluminum oil pan.
It surely is. Or even stripping the threaded insert in a cast iron oil pan, because then you can’t even remove the drain plug, so you have to swap the whole sump, while it’s still full of oil. Guess how I know.
Not a fun time.
The studs should be stamped with a grade #. Likely either 8.8 or 10.9 for metric. This tells you the minimum tensile strength, so no need for fancy lab testing. 8.8 = 800 MPa min and 10.9 = 1040 MPa.
Stronger isn’t always better. The torque is the “pre-load”, but many joints will see additional loads of varying magnitude and direction. Due to this, you want to reach ~70%-90% of yield strength through torque to avoid additional tensile elastic deformation under loads which would cause the joints clamp strength to reduce.
Bolted Joints theory is actually somewhat complicated and very fascinating. There are several other factors to consider beyond meeting target stress relative to yield strength through torque.
I have to wonder if it’s a sign of truth in owner stereotypes? Nissans are run on all-seasons until they’re good and used-up while Subarus get swapped between winter and summer tires on the regular?
Subaru also recommends a tire rotation every 5k miles which almost every Subaru owner does.