RV Tire Safety
with RV tire expert Roger Marble
I was following a forum thread on using closed state scales to learn your “four corner weights.” This is possible in Washington, Oregon, and some other states.
Some commenters felt the practice was not wise as the area around the platform scale might not be perfectly flat. I posted my thoughts on the topic, as follows:
Not sure if I understand the concern over the accuracy of using a large platform scale to try and get a handle on your side-to-side loading.
I have a blog post on “Measurable vs Meaningful” that some might want to review.
When setting the inflation based on the published Load & Inflation tables, you should always “err on the high side.” This means if your measured weight were 2,005# you should go UP to the first weight that exceeded 2,005# and maybe even higher.
Let’s assume the table for your tire gave 90 psi at 1,900# and 95 psi at 2,210#. I would recommend you select 95 psi as your MINIMUM inflation. But what would you do if the chart for your tire showed an inflation for 2,010# or 2,005# or 2,000#? Would you cut things so fine as to select the inflation for these loads? I hope not. What might happen if 50 minutes after getting the tire loads you top off the fuel and buy some groceries? You are now most certainly over the measured 2,005#. Are you gonna run back to the scales? I wouldn’t, and I would not need to as I have a built-in cushion of load capacity over the minimum needed to support my actual load.
We haven’t addressed the question of your tire pressure gauge accuracy. Unless you have access to ISO Certified laboratory gauges, as I do, you probably need to assume that your gauge is off by at least one increment reading of the pressure scale. For some truck type stick gauges that means 5 psi. What is your cushion that covers your gauge accuracy?
My “cushion” results from a few actions:
1. I always go up in the charts to the next inflation level and if my measured load is within 100# of a level, I will go up TWO levels of inflation which would be 10 psi.
2. I also add 10% to the selected table inflation and again round up to the next “0” or “x5” pressure.
The additional 10% means you can avoid having to chase the Cold Inflation level every morning when the temperature drops and pressure drops a few psi.
When I checked my “four corner weights” on the state scale, was the area beside the platform exactly level? No, it wasn’t, but it looks close enough that even if my weight was off by 100# my other adjustments would more than compensate.
Read more from Roger Marble on his blog at RVtiresafety.net.