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Monday, March 4, 2024

Do I need to balance my RV tires?

 I was recently asked about tire balancing.

Reasonable question but as always the answer starts off wit "It Depends"

Vibration can be because of a tire/wheel suspension component is out of balance. Vibration can also occur because the tire or tire and wheel assy is not "round". On a small (14' to 16") tire you can see and measure out of round when the tire & wheel are placed on a spin balancer.   I have shown that you can "balance" a square cement block

  so you need to be sure your tire & wheel assy is "round within at least 0.030"

The person asking the question, said that they had done some research and learned there were three methods. They wanted to understand the advantages of each and which they should use for their Class-A RV.

The basic method is static or "bubble balance". as seen in this  video

The mounted tire is placed on a balance and the heavy spot is counter balanced with weights.

This static balancing is lower cost but does not provide the best balance. This method is not usually done any more by full service tire stores as it only affects the "static" imbalance and with today's light weight cars the driver is more likely to feel even a minor imbalance. I once had a car with one front tire 1/4 oz out of balance and on a very smooth portion of the interstate on my way home from work I would occasionally got steering wheel movement. A re-check at the store solved the problem. The car was a small light weight sports car and it just happened to be sensitive at that level. My one-ton dually pickup was not sensitive at the two ounce level on the rear axle.

The next best method would be with the mounted tire on a "spin balancer", This rotates the wheel and tire at speed and electronically calculates where to place the weights.
When you buy a new passenger or pick-up truck tire, this is the method they are normally talking about.

But truck/bus size tires can also be balanced using a heavy duty version of this type of machine.

Spin balancers measures the up-down imbalance and the side to side balance and tells the operator how much weight to place on both the inside and the outside of the wheel to counteract forces in both directions.

 Finally there would be "On-Vehicle" spin balance this would give the balance for the tire, wheel and the brake drum and hub of the vehicle so if the drum was slightly out of balance it would be included and weights would counter balance all the spinning components. If you get this type of balancing done it is important to mark the wheel position on the hub if you ever remove the wheel to check brakes and to re-mount the wheel in the exact same orientation. A downside to this method is that it can't be done to tires on drive axles.

Many drivers of Class-A do not balance their tires as they do not feel the imbalance. Some others always balance the fronts because the driver & co-pilot are sitting almost on top of the tires. On-vehicle spin would probably give the best results but this would be for the front only. Here is a video showing the process on a Corvette
 but RV tires would be the same process but with HD bigger equipment.

I see little reason to balance the rear duals on a Class-A as you will not feel the balance problem unless something was very out of balance.

Some additional info in another post.

For Class-A I think you can just take the RV out for a quick test drive on a nice section of smooth Interstate. If you feel shaking either through the steering wheel or floorboards then you would go and have the front tires "on-vehicle spin balanced".

For Class-C and smaller vehicles using 16" diameter LT type tires I would spin balance all six assemblies.

Saturday, February 24, 2024

How much air pressure do my motorhome tires need?


Tire loads and proper inflation for motorhomes

Today’s key points: Know the minimum tire inflation based on tire industry guidelines. The basic instruction for your minimum RV tire maintenance is to check your inflation with a good gauge at least monthly and every morning before travel.

Tire inflation seems to be a topic that confuses some and has others believing in misleading or just plain incorrect information. Tire inflation is one item that directly affects the safety of your RV, truck, or car as you travel down the highway. Many of my posts have outlined information that you really should know and understand. The intent of these posts is to give you a better foundation of understanding more about tires. But if you only pay attention to one series of posts, this is it.

Tires do not carry the load

Some people have been led to believe that the load is carried by just the tire sidewall. This is not correct. Tires are just a container of air. It is the inflation air that does the work. Think for a moment of an impact wrench. It can’t do the work of loosening or tightening nuts on your wheels without the air. A tire can’t do the work of carrying the load or providing the traction needed to turn, start or stop if it doesn’t have air. The load a tire can carry is based on the air volume in the tire and the pressure of that air inside the tire. You can see this if you look at any Load & Inflation chart, as found HERE.

 it is important to understand that these tables are essentially identical across all tire companies that are making the same size tire.

Load Range vs. Ply Rating

Some people believe that tires with a higher Load Range can carry more load at the same inflation. This is just not correct. Don’t forget that the term Load Range replaced Ply Rating with the introduction of radial tires to replace bias tires. You would be hard-pressed to measure the uninflated load capability difference between a Load Range D and E tire or between a G or H Load Range tire.

If you still think the load is supported by the tire construction, I would challenge you to find a Load vs. Construction table. Here is an example of a Load & Inflation table for a 255/70R22.5 and it covers both LR-G and LR-H tires in that size.



 Sidewall stamping examples

Here are sidewall stamping aka “marking” examples from a large P-type tire showing the dimensions, along with Load Index and Speed Rating. An LT-type tire would look similar except that LT-type tires and Commercial Truck/Bus (22.5″) can be applied as single or dual (side by side). So they would have two sets of numbers for the Load Index (single and dual application). Commercial truck tires are not speed rated, but Michelin and Goodyear and others indicate a 75 mph Max operating speed in RV applications no matter what the tire rating is.


 Here are the tire reinforcement materials, both type and quantity.



Next, we see the Load and Inflation ratings for this standard load P-type tire.



Nowhere do we see a statement on construction or Load Range for various inflations and different load capacities for different constructions.