This week we've been attending the Airstream Club's "International Rally" in Sedalia, Missouri—and it has been a great experience. One of the highlights for me was attending a seminar by Bill Snider of Dexter Axle Group, because Bill did an excellent job of explaining how trailer brakes, bearings, and other components do their job.
Perhaps the most interesting topic for me was the explanation of why trailer wheels come flying off Airstreams much more often than other vehicles.
I'm often asked by people "Why do I need a torque wrench for my Airstream, when I don't need one for the wheels on my car?" That's a really good question. Let's dig into that.
The answer starts with the fact that most late-model Airstream trailers have aluminum wheels. Aluminum wheels aren't as flexible as steel wheels, so in order to get them to fit properly to the brake hub, you need to apply just the right amount of pressure. That pressure is determined by how much you tighten the lug nuts.
A steel wheel doesn't need as much tightening of the lug nuts. Typically you'll see a manufacturer recommendation of about 70 to 95 ft-lbs, as measured by a torque wrench. Because steel bends more readily, the steel wheel will fit snugly to the hub with that amount of pressure.
With aluminum, which is stiffer, you need higher torque. Typically that's 110 ft-lbs for an Airstream, and it needs to be pretty accurate in order for the wheel to mate well to the hub.
So now you might be thinking, "Seems like it would be better to just make sure those lug nuts are really tight, so the aluminum wheel stays on." Alas, it's not that simple.
The lug bolts (the threaded part that you screw the lug nut onto) might look like simple parts, but they are actually highly engineered. There's a lot of science going into them.
First off, those lug bolts have to carry a lot of weight. On your car, which might weigh 3,000-3,500 pounds, you'll usually have 5 lug bolts per wheel, which means a total of 20 bolts. That's 150-175 pounds per bolt.
Compare that to a typical Airstream. A late-model 25 foot Airstream will typically weigh about 7,000 pounds when loaded, and it has 24 lug bolts (6 per wheel). That's 292 pounds per bolt. So the lug bolts are doing double the work compared to your car.
Not only that, but when you turn a corner with a trailer, the side forces are basically trying to tear the wheels off. That's even more strain for the wheel lug bolts.
Second, when tightened properly, the lug bolt should stretch about 5/1000 of an inch, kind of like a very stiff spring. You can't see that, of course, and yet it is absolutely critical.
If the lug bolt is overtightened (stretched too much), it will eventually break under the stress—and your trailer wheel will go flying off. That's what happened in the photo above. A mechanic overtightened the nuts, and shortly afterward five of the bolts snapped clean off, leaving only one. (By the way, the wheel did considerable damage to the Airstream as it departed.)
Dexter says that the lug bolts provided with our trailers have a maximum torque rating of 120 ft-lbs.
If the lug bolt is undertightened (not stretched enough), the nut will eventually vibrate loose —and your trailer wheel will come flying off. Either way, it's a bad day for you.
In the case of Airstream, the factory torque spec is 110 ft-lbs for late model trailers with aluminum wheels. So you can't just tighten the nuts until they "feel" right. Even an experienced mechanic can't accurately judge the difference between 100, 110, and 120 ft-lbs.
The only way to get it right is with a torque wrench. Now you know why we put a torque wrench in our Tire Changing Kit.
A few more tips:
- Check the lug nut torque on your wheel every time you replace a tire, and then again at 10 miles, 25 miles, and 50 miles, to be sure the nuts are properly seated and torqued. After that, the nuts should stay in place.
- Don't ever use any sort of lubricant, anti-seize, or other compounds on the threads (they should be dry).
- Dexter's recommendation is to re-check the torque every 3,000 miles. I personally think that's overkill, but it won't hurt. You can't over-tighten the lug nuts by checking them with a torque wrench.
- There's no need or benefit to "re-torque" the nuts by backing them off, and then tightening them again. Just check them.
- Keep your torque wrench in its protective case, and always wind it back down to zero or below 10 ft-lbs when you're done using it.
If don't have a torque wrench or aren't sure how to use one, watch this video, which explains how to master the basics:
11 comments
Barry Connors
Iam sure my airstream dealership never used a torque wrench because even tires where way under inflated when picked airstream up 50 psi
Do u recommend undoing lug nuts and re-tighten with torque wrench?
Brian Powers
Key note: when I have my tires replaced, I insist on overseeing the technician tighten the Lug Nuts with a torque wrench. I even offer mine that I set to 110 lbs for my aluminum wheels,
Once on the road I then retorque the lug nuts as described in the article and trust me there is always a Lug Nut or two that need tightening. Then you will get to a point that none of the Lug Nuts need tightening. When that happens I randomly check them just to make sure.
Nancy M
Excellent explanation as always Rich! Thank you!
William
Thanks for all this detail.
I’ve had issues getting my lug nuts off
Two years ago when I purchased my used 2017 28’ Flying Cloud I got new tires at Discount Tire they struggled getting the lug nuts off. We replaced a few at that time. Just last week one of the valve stems failed and it went flat (23psi) luckily a couple miles from our destination – glad we have TPMS. A few days later, I aired up the flat and that’s when the metal/rubber valve stem failed completely. The metal core came out. I put the spare on at that time but struggled to get the lug nuts off. One was buggered up and gave me the most trouble. I used the breaker bar in your tire kit to finally get it off. My Makita impact wrench worked on the other 5 but struggled. All the nuts showed signs of rust. I towed it with 5 lug nuts the 3 miles to Discount Tire. They had a tool to fix the threads. I had all 4 valve stems replaced with all metal stems and had new lug nuts installed. I was looking into using anti seize lube but found online that that was a bad idea as the torque value is set for a dry connection and the anti seize lube would change all that. Now I’m thinking of cleaning all the lug bolts with a wire brush but that’s a whole lot of work.
Any ideas on how to make those lug nuts easier to remove?
William Cruze
I have always torqued, but now I know a little more why. Good info, thanks.
CPT(R) Richard D VanOrsdale
Very well written article! It might be just some OCD on my part, but, I routinely confirm the torques on our 30-ft Flying Cloud every approximately 2000 miles. Rarely is a nut requiring more torque, but, it does happen. Rarely. I love towing our Airstream , especially knowing our tire pressures and temperatures (via our TPMS) and that the nut torques are proper.
John Downs
Rich,
Great article, just one comment. I believe most new cars have aluminum wheels not steel.
We own one car, two suvs and one truck, all GM. All the owner’s manuals require the wheels to be torqued to 140 pounds when being reinstalled.
Michael Carden
Excellent article Rich. Helpful as well because I was under the mistaken impression that I should check my 2014 Flying Cloud 19’ lug nuts at least monthly. I probably will keep doing that but at least now I know that every 3,000 miles or so is adequate. As a new RVer I highly value your articles and gear. Thanks very much.
Jeffrey Curtis
I can attest to getting antisieze on the threads. This happened accidentally during a brake job on our Subaru. I had to tighten the bolts after every drive until I sprayed the bolts and lug nuts with parts cleaner and wiped them down.
Douglas Fackelman
Air Gear ROCKS!! LOVE you guys, your products, your guidance, and support! Thank you!!
Gear we have: Tire Changing Kit, TST 507 TPMS
Airstream: 2020 16’ Caravel; single axle.
I have a question on the topic of torquing the wheels that was precipitated by the hub cap on the wheels. The hubcap is pinched between the wheel and the mounting plate with the lug bolts. That hub cap rattled and rattled, even after I checked the torque periodically. I recently experienced the awesome value of the TST 507 pay off!! Had a wheel get out of balance and create a flat spot. The TPMS detected a loss of pressure formed at the flat spot and immediately alerted us, giving us time to safely pull over. Swapped out the spare just fine. While torquing the spare into place as directed I noticed the hub cap no longer rattled!!!
Here’s the question…is a hub cap that rattles an indicator of a wheel that is not properly seated? When I torqued the wheels periodically I didn’t off-weight the wheel as I did following the process of putting on the spare. Also, after getting new tires installed now both hubcaps rattle a bit. So back to the question: Is a hubcap that rattles an indication of wheels not seated right?
Rich Luhr
ANSWERS:
Barry Connors: Tire pressure and torque aren’t related. The first measures the air pressure in the tire, and the second measures the tightness of the lug nuts/bolts. You don’t need to loosen the lug nuts in order to check them, but it won’t hurt.
William: Sounds like your lug nuts might be corroded or have damaged threads. I can’t diagnose the problem accurately without examining them, but you should consider having all the lug bolts replaced. It’s actually not a terrible job. I did two wheels in a parking lot while on trip. For that story, see https://tour.airstreamlife.com/wordpress/?p=297
Douglas Fackelman: No, the rattling hub cap isn’t a reliable indicator of anything. It might be rattling because of any number of small issues (damage, pebbles, etc). The important thing is to make sure the torque is correct on all the lug nuts. If the torque is correct, the wheel should be properly seated.