A friend asked me this question, along with the companion of “How Tight?” The last thing we want is to lose a wheel — because it will not only delay our trip, but a wheel coming loose can do serious damage — to us, our stuff, or maybe even kill someone. That’s NOT what we want, so tighten the trailer wheel bolts!
But, How tight? And, How often?
I see a lot of trailers along the highway with missing wheels. Some have come off because of loose bolts, and others with bearing failures. Of course, some just go flat, and some have another tire disaster, but we’ve covered much of that in the Trailer Spare Tires article.
So what about the bolts? Or, maybe on your trailer, the Nuts? — Also called “Lugs” “Lug Bolts” or “Lug Nuts”.
Trailer Wheel Bolts
There are 2 ways trailer wheels typically attach. First, with bolts that thread into the wheel hub. “Lug Bolts”. The hub has holes with threads, and the bolts screw in. Second, some trailer wheels attach with a nut that goes onto a stud that is captured in the hub. “Lug Nuts”.
There really isn’t much difference with respect to when to tighten the trailer wheel bolts, but it’s worth showing the difference anyway.
As you can see in the images, these “Lug Bolt” and “Lug Nut” fasteners differ from regular bolts because they have a large taper under the head. It’s kind of like the taper on a flat head bolt, but normally lug bolts have raised hex heads. And, lug nuts are hex with an extended taper.
The taper on the bolt (or nut) meets with a similar chamfer in the bolt hole on the wheel. As the 2 taper surfaces meet, tightening creates forces to center the bolt in the hole. And, when they are all installed, to center the wheel on the hub.
Nuts and Bolts act basically the same with the taper, so the same wheel can be used for both. You can see that in the image above. We use the nuts if the axle has studs sticking out, or lug bolts if the hubs have threaded holes. They do the same job.
How To Tighten Trailer Wheel Bolts
When installing a wheel, it’s best to start all the lugs first, then pull them in a little at a time rotating around the bolt pattern. This gives the best chance of getting the wheel at perfect center. It’s a simple process to tighten trailer wheel bolts, and here’s a quick video to explain it.
Why do you need this bolt tightening process? Does it really matter?
The theory says if you tighten the wheel bolts in a cross pattern, a little at a time as shown, then the wheel pulls to center and flat against the hub. That’s what we want. On the other hand, if you tighten one bolt all the way when the others are loose, then the wheel does not “set” perfectly. If all the machining for the wheel, the hub and the bolts are perfect, then perhaps it wouldn’t matter. While it’s a nice thought, machining is not all perfect. So, we nest the wheel onto the hub and center it by tightening in a pattern. This also makes sure all of the bolts end up equally tight.
What If You Don’t?
OK, what if you don’t use a tightening pattern? Well, maybe not much, but experience says the bolts will come loose. Try it on your trailer. Tighten them all one at a time as if it’s done. Then, go back with your wrench and feel which ones are tighter. They will not all be equally tight.
As the trailer tire turns carrying the trailer load, the wheel wants to move if it can. Since the holes are all tapered, if one is all the way tight first, then the others don’t seat perfectly, and this will allow minuscule movements, which will eventually allow bolts (or nuts) to work loose.
This same phenomena happens if the wheel is under load when you put the bolts on. (Like if you don’t jack up the axle first.) The load doesn’t allow the wheel to center and seat properly. When it turns going down the road, it has just enough space for things to work loose. Not to mention it will be a little out of balance.
On the other hand, if you use the process tightening a little at a time, working around the bolt pattern, all of the bolts will end up equally tight, and the trailer wheel will end up at center. This is the best way to make sure the trailer wheels, once tight, won’t inherently want to work themselves loose.
Seriously, this is one of those times when it does NOT help to work fast and take short-cuts.
Our starting question is “How often should you tighten trailer wheel bolts?” The answer: After having the wheels off, check them after driving just a bit. If everything is tight, you can extend the interval for checking.
When they are always tight, it gives you confidence that they’ll stay tight, so you can check less often. When traveling, check things when you stop for fuel. I just look things over, then put my hand on the hubs to check temperature. If I’ve recently done something that took the wheels off, then I put a lug wrench on to see if everything is tight. As above, if they stay tight for a few times checking, then I gain confidence and don’t check nearly as often.
If the wheels are aluminum, check them more often. Aluminum and steel expand differently for heat or cold, so check bolt torque more often.
On the other hand, if you ever find one loose, tighten it, then check again more frequently. If more than one is loose, jack up the axle, remove the bolts, then clean the hub and wheel. Tighten the trailer wheel bolts with the sequence again, and make sure the torque is right.
Proper bolt torque depends on the bolt size. If you can, look for the manufacturer specifications. If not, use this generic info. I recommend using a torque wrench — a clicker type is not that expensive and it’s a very useful tool.
Typically trailer wheel bolts are 1/2″-20 threads and usually Grade 5 or Grade 8. (See the article “How To Choose Bolts“.) For these, tighten to 90 ft-lbs if the wheel is steel. Maybe only 80 ft-lbs for aluminum wheels — then check the aluminum wheels more often.
If you have 9/16″ bolts, tighten to 125 ft-lbs (steel), or 105 ft-lbs for aluminum wheels. These are typically used on larger capacity axles. For other bolt sizes, check the manufacturer’s specs.
Why less torque for aluminum wheels? If you over tighten aluminum, I’ve heard they can crack (over time). I don’t have experience with this, so don’t take my word for it. Best to check with the manufacturer before you over-tighten your trailer wheel bolts.
If you don’t have a torque wrench, tighten them about as tight as humanly possible with the lug wrench (without hurting yourself). Obviously, if you’re a big strong person, don’t go as tight as humanly possible. If you’re a small person, or not very strong, get someone to help you. Either way, take it to a shop and have it torqued correctly. Proper torque is one of the best ways to make sure trailer wheel bolts do not come loose.
It’s important to have them good and tight. If in doubt, check them each time you stop — until you are confident they are not coming loose.
By the way, don’t use grease on lugs. That will just help them come loose. Use an Anti-Seize instead, especially if you use the trailer in and around water. Find one specific for bolts, but do NOT use grease.
Dealing With Damage?
Lugs and Lug Bolts (even Lug nuts) sometimes get damage. That makes it hard to properly tighten trailer wheel bolts, but it’s something we can fix. Let’s take these one at a time.
If a Lug Bolt or Lug Nut has damage (like thread damage), just replace it. They are very common on-line and in local trailer stores. You just have to know the thread designation, and the length. See above.
If a lug has damage, sometimes you can repair it with a thread die. If the damage is more than that, replace it. The Lugs press in from the back on the hub (or brake drum), so they can also press out. Please DON’T hammer them out as you can injure other parts of the axle. Use a bolt puller or a large clamp. I usually use a large deep well socket (over the bolt head) and large size C-clamp.
The splines on the lug dig into the parent metal, so they do take high force to take out or put in. Just press the bad one out, then get a new one to match, and press it in.
Finally, the internal threads in a hub (if you have this kind) can usually be repaired using a tap. Just match the thread of the bolt, then carefully chase the threads.
There are some good videos on YouTube for doing these repairs, but watch a few to be sure because there are some loose cannons out there making videos.
Summing Up Trailer Wheel Bolts
That’s about it. There’s no reason for a wheel to come off because of loose bolts. It’s easy to check, and easy to tighten things. It’s just a part of typical trailer maintenance we do before for a trip. If you use the trailer more frequently (like with your work), check things on a regular schedule, like once a month. Good luck.
One final note. If you carry a load that is especially important, or if you have wheels that just don’t want to stay tight, consider other ways of capturing the bolts. Wired nuts are a great solution. (Small hole in the side of the nut, then run a wire through it and connect them all together. This keeps them from coming off.) Or use a tab plate. (Usually sheetmetal plate that the bolts also go through. After you tighten the bolts, bend the tabs up against the hex sides to keep them from rotating off.) Do a little research if you think these are needed for your trailer wheel bolts.
By the way, let us know if you have other good tips to tighten trailer wheel bolts, or about when you do it.