If you have a “tag” axle on your Class A or you have a multi-axle towable trailer or 5th wheel, you may have noticed the tread surface of some of your tires shows “scrubbing” or side slip. Sometimes you even see black marks left on the pavement from your tires. Why? Is there something wrong with your setup?
You try to avoid sharp turns and U-turns as much as possible, but still see visible signs of side scrubbing on the tread of your tires.
Visual inspection
First, you do want to confirm with a visual inspection that mounting bolts and brackets are all in good condition and do not show evidence of damage or bending, similar to what we see here:
If you have bent or damaged suspension components, these things should be fixed before you continue.
Next, confirm tire alignment
When your RV passes the visual inspection, you then need to confirm the tires are within spec for “alignment”. For these tires, alignment would be Camber and Toe (in or out).
Here is a nice example of Toe (looking down on the tires with the front toward the top of the picture):
And here is Camber seen from the rear of a left side tire:
Your RV dealer should be able to tell you the spec for both Camber and Toe for your RV. If not, I would suggest you find a better, more competent dealer. I believe that both Toe and Camber on trailers would be near 0, but go with the spec from the RV company.
Measure the camber
You can search for an alignment shop that can check your RV, but you don’t have to spend a lot of money to confirm how close to spec you are. You can measure the camber with a “magnetic camber tool” ( about $12 for a basic gauge to $50 for the digital version at Amazon).
The Toe can be measured with tape measure and a friend to learn if the “Toe” has the front of the tires closer together than the rear of the tires on each axle.
Before you take these measurements, be sure you are on relatively flat, smooth and hard surface. If you are working with a tag axle, you need to learn and confirm how to make sure the RV suspension is in the same condition as it would be when driving down the highway. Some “tag” suspensions may lift the axle at low speeds or make some adjustment when trying to back up. Ideally you would move the RV forward and back a couple of times, in a straight line, for about 1-1/2 tire revolution to “unload” and twist from the tires turning onto the test location.
Once you have measured your axles you can see if you need to have some adjustment made or if you have bent or damaged suspension components.
Cause of tire tread scrubs
Once you have confirmed that axle alignment isn’t the problem, the answer is that the trailer tires are being dragged around every corner not driven or steered. Here is a rough sketch that shows why the tire tread scrubs. The center of tire rotation is not pointed to the center of the turn radius so the tires are always being dragged around every turn. It is just worse on tight turns. This is just a rough sketch, but I think you will get the idea.
Lowering the percentage of max load capacity of the tire is a good idea. You can achieve this by reducing the actual load on your tires or increasing the inflation to the “max” on the tire sidewall. Don’t forget that it is the air pressure that determines the load capacity, not the Load Range (E, G to H), and certainly not the “Ply Rating”.
You will gain nothing from a Load Range change if you do not also increase the air pressure. You do need to confirm the wheel max psi capacity which, for some wheels, is not easy to do as some wheel manufacturers do not have high pressure ratings easily available.
Regarding tread compound: Sometimes it isn’t just the hardness of the rubber but also the tread pattern that can affect scrubbing wear.
In general, the tread scrub is a function of dragging a trailer around.
Roger Marble
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I think that using the proper ST tire is also important. I have seen LT tires installed on dual axle trailers. These tires, while rated for the load, are not designed for the scuffing. The sidewalls flex more and put undo stress on the tires, especially if they have a more aggressive tread. Yes, most are less expensive than good ST tires, but are not designed for the purpose.
Thank you, Roger! RV #1 had a non-stearable tag. RV #2 has no tag. If there is a #3 RV, then I anticipate the tag will be stearable. That would eliminate as much scrubbing as possible, wouldn’t it? Have a great day, a good Thanksgiving, and safe travels!