We have heard of wheels coming off trailers and caravans over the years. Fortunately these were few and far between and there were no major accidents.However, all of these were always on the passenger side. This prompted us for a deep understanding to get to the root cause.
The image below right is a typical sheared stud when losing a wheel.
We appreciate and acknowledge the assistance of Toyota’s Head Office Engineering staff in giving us access to several documents and for their deep technical advice. They do point out the requirement for legal disclaimers and why a lot of this information is not published. So we are at pains to point out that this is a guide to assist you and not a definitive statement on how to keep your wheel nuts and wheels correctly secure. You must always follow the settings by the wheel manufacturer. In the case of Kimberley wheel/hubs, you may follow this guide.
This is a summary of our findings and recommendations.
Following this is a more in-depth discussion and you can download a copy of a Toyota Service Guide “Installing Alloy Wheels".
Summary of Findings:
The Root Cause is either:
- Heat and vibration can cause the left side (passenger) wheel nuts to become loose, once there is less than the required torque. This is because of the direction of rotation. Over time the nuts on this side will ALWAYS loosen when subjected to vibration typical on dirt roads.
- In Tandem caravans this will accelerate because when cornering, the tandem wheel combination creates additional lateral forces.
- Use of an anti seizure product on wheels nuts (like WD-40)
- Incorrect wheel positioning on the hub and/or incorrect nut profile/ clearances for the wheel (usually on alloy wheels and usually with non genuine alloys)
- Incorrect wheel nut torque (see table at end for Toyota Landcruiser. Note each vehicle has a different setting and this does change for alloy wheels compared to steel. Alloy torque settings are usually higher.)
- Incorrect wheel nut tightening sequence (Linked to the point above) See correct sequence in photo on right.
- The Dome nuts do not mate on the wheel surface. This is either because of debris or excess sealant inside the dome nut or the inside nut thread length is too short. This can occur with different alloy wheels with less thickness around the stud. The nuts then “bottom out” before becoming tight against the wheels.
It is easy to see if the wheel is centred correctly and the wheel nuts are correct. If they are correct, then the middle 2 points are the most probable cause in all cases of losing a wheel.
Note, we have heard of many situations when there is a wheel vibration on a trailer or caravan. The instictive investigation is to check wheel balancing. Yet, if the wheel is alloy and is not centric on the hub as required for Toyota wheeels in particular, you will experience vibration. There is a high risk of losing wheel nuts in this situation.
Symptoms to note:
- Using a non-original alloy wheel needs careful examination of the surfaces and the centricity of the hub, nut turning clearances and choice of nut.
- If your “passenger side” wheel nuts are loosening> re-torque your wheels and continue to do random check every 100klms until they appear stable. After loosening, the nuts WILL roll off. After losing some nuts, the wheel studs snap off and the wheel comes off.
- If your drivers side studs are breaking> although you are not losing wheel nuts on this side, they are loose. The studs then break off because of fatigue. Check that the nuts are not under-torqued and re-torque following the tightening sequence
- The thermal expansion of alloy wheels is greater than the steel hub. After excessive breaking with the resultant high disc-rotor heat, check the torque on your wheel nuts. This will be even greater on magnet drum breaks as the drum break assembly directly houses the wheel studs.
- Never ever use WD-40 or an equivalent. Never, ever.
Checking the torque of your wheel nuts while travelling
- Correct torque settings on the wheel studs in the correct sequence. In the case of alloy wheels and "flat nuts", this can be very high. In the published Toyota guide attached it is 131Nm.
- Installing reverse thread (left hand thread) wheel studs for passenger side of trailer/ caravan.
- Use of wheel nut “pointers” that show any movement in the wheel nut (commonly seen on trucks).
- Use of Loctite or equivalent. There is only ONE version of this product (Loctite 290) that will assist but it also makes wheel removal more difficult.
- Random check of toque settings using torque sticks every 200 klms or so in a high vibration environment.
To check the nuts just apply the toque stick or extension and see if the correct torque is on the nut. This is only a rough guide because of latent friction, but it will serve the purpose while travelling. If it is loose, then re-torque all the nuts following the correct pattern.
The correct way to re-torque your trailer/caravan wheel nuts when travelling is to loosen one a little and then re-tighten. There is a buildup of surface friction when they are left alone for a while.
It is important you tighten up your bolts in a fluid motion in order to get an accurate torque reading.
Why passenger wheel nuts will always come loose in a vibration environment without constant attention.
Quote from a well know forum (author not shown for privacy reasons):
“I own 3 Isuzu trucks and they all have left hand threaded wheel nuts on the left side. They are left hand threaded so they don't unscrew.
I also do several hundred thousand km a year in Toyota Landcruisers on corrugated dirt roads. Over the years I have had wheels come lose from time to time --always the left side, never the right. This information I have posted comes from experience not a book or a website.
The same thing applies to CV's on the off-road buggies we race.
Only the bolts that have the bolt head on the left side come loose. That is gearbox CV on left side, wheel CV on right side.”
Why is this?
The nuts have to be loose in the first place. And this is from incorrect toque of the nut AND/OR alloy wheel expansion and contraction from heat.
The mechanism for the left side wheel nuts spinning off as the vehicle travels can be understood from the geometry of the wheel and studs when the wheel is slightly loose. Since the stud holes are larger than the studs, the wheel is not perfectly concentric with the axle when the nuts are loose. When the road pushes up on the tire, the wheel tends to be pushed up relative to the axle centerline. This means the wheel centerline is slightly above the axle centerline. This centerline offset gives rise to a relative velocity vector between each wheel nut and the part of the wheel the nuts touch. This vector is in the loosening direction on the left side when the vehicle is driving forward and is the cause of wheel nuts spinning off the left side.
The right side nuts have that same relative velocity vector, but in the opposite (i.e., tightening) direction. It turns out that this vector is not strong enough to make a loose nut tight again. So, on the right side, a loose nut tends to stay loose rather than spin off. But this invites another mechanism – fatigue. When a nut is tight, the clamping force creates large frictional forces at the wheel/hub interface that transfer the vertical forces that support the weight of the car. However, when a nut is loose, there is no clamping force, and the studs now carry the vertical forces. This bends the studs up and down every time the tire rotates. Just as a paper clip breaks when you bend it back and forth a few times, a wheel stud can break when it is bent up and down a few million times. This is called reversed-bending fatigue, and is the reason that right-side studs eventually break off when the nuts are loose.
The starting point for a wheel nut to spin off the left side, or for a stud to break off the right side, is the same: the nut had to be loose to start with.
Torqueing Wheel Nuts and Heat
The British Standard recommends retorqueing after 30 minutes or after 40 to 80 km. When this procedure was tested in 1995 it was found that some nuts slackened a little after 160km. For an operation with hilly routes when the brakes get hot, the slackening might be expected to be more pronounced because it has been reported that studs start to creep when temperatures exceed 200 degrees Celsius. This can occur after excessive braking.
Correct torque for Kimberley Hubs
Follow the torque settings for the vehicle that the hubs are matched to. This is because the number of studs and the size of the studs are matched to that vehicle. So if you have the Toyota 200 Series pattern of 5 x 14mm studs, follow the torque settings for this vehicle matched to the wheel chosen.
The broad generalized guide for Toyota 200 series Landcruisers with Alloy wheels is set to 131Nm as shown in the attached document.
You can download this Toyota Document for Toyota Landcruisers here