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Tire Facts
The subject of tires seems to be one discussed frequently on the Tiffin RV Network. This topic, will deal with a lot of the questions that are asked by forum members:
Tire Basics:
Simply put, a tire is a vessel that contains air. This combination or air and tire support your motorhome and its contents. That not only means your material items, but your children, your spouse, perhaps your grandkids. Thus, tires are a very important safety item and one that should demand your attention.
Air Pressure:
In my view, proper air pressure is one of the least understood principals. Yet, it is one of the most important factors there is if one is two obtain the maximum safety and life from one's Motorhome tires.
A tire that is underinflated:
- Builds up excessive heat
- Is unstable
- Causes poor steering and road handling
- Wears Unevenly
- Decreases gas mileage performance
- Produces soft ride
A tire that is overinflated:
- Reduces the tire's footprint
- Reduces Traction
- Reduces Braking
- Causes poor steering
- Produces hard ride
What is the proper or correct air pressure?
The answer is very simply: The correct air pressure the tire needs depends entirely on the weight of your fully loaded Motorhome. You cannot determine this unless you know the entire weight of your Motorhome. Anything else is merely a guess. This is why it is so important to properly weigh your Motorhome. Notice I state properly weigh. There is a weighing process that will generate the correct data to enable one to determine the correct air pressure to carry in the Motorhome tires as well as determine if the Motorhome is overloaded or not. For more details on how to properly weigh your motorhome please check out the topics in the "weighing" category in this library.
How to determine the correct tire air pressure for your tires?
For the purposes of this subject, let’s assume you just properly weighed (all four corners), your 2003 Tiffin Bus and found the following actual weight of the four corners or wheel sets:
Left Front = 4,987 lbs. Right Front = 4,846 lbs. Left Rear = 9,510 lbs. Right Rear = 9,679 lbs.
For now we'll assume your Allegro Bus has Michelin XRV Tires size: 255/80R/22.5. So now we go to www.michelinrvtires.com and find the Load Inflation Table for the XRV tire
Once we locate it, we next look and see from our weigh data that our highest weight on the front is (4,987 lbs.), we find from the chart that 4,975 lbs. calls for 100 PSI & 5,150 lbs. calls for 105 PSI. The difference between 5,150 and 4,975 is 75 lbs so we know that for every 15 lb. differential in weight we should add 1 lb. PSI over the recommended. The motorhome front end's highest weight was found to be 4,987 which is 12 lbs over 4,975. Therefore the proper inflation rate for the front end tires is 101 PSI. This is the proper air pressure for the weight being placed on the tire. The reason we used the highest weight on the front was that it governs what pressure is used for all the tires on that axle. In this case the Left Front was the heaviest.
For the rear tires, from the actual weight we see that the Right Rear was weighed at 9,679 lbs. Consulting the load inflation chart we find that we are overloaded (9,679 (actual) – 9610 (table) = 69 lbs.). The maximum air pressure we can inflate the tire is 110 PSI. We really should also see if we couldn’t relocate the 69 lbs or eliminate it. So in summation the proper air pressure for the weight placed on the axles is 101 lbs. for the front tires and 110 PSI. for the rear tires. Anything else is simply guessing and either underinflating or overinflating the tire(s) for the weight being placed on them.
Note: You tires may not be the same as the above example. Be sure to consult the tire manufacturer's pressure/load tables for your specific tires at www.michelinrvtires.com or www.goodyear.com/rv/tirecare/loadinflationtables.html for specific information for your own RV.
Submitted by Mike Sundberg - 3/27/06
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