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Monday, June 19, 2017

Another example of learning correct tire inflation

Originally Posted by Ron View Post
Tireman9 and others....I just ran my coach over to the local Cat Scales at a truck stop nearby. As I stated earlier they do not make things easy and a 6" curb on each side of the scales prevented me from putting each side on separately so that I could get a close four corner figure. I settled on the two axle approach. All tanks were full, (water tank was actually just over 2/3, it fills very slowly and I got bored). Front axle came in at 11,400 lbs, rear axle was 16,560 lbs. My front axle is rated at 13,300 lbs and the rear is 21,000 lbs with a GVW of 34,300 lbs. 295-75R-22.5 tires. I have looked at the tables but would like to see what you folks come up with for approx. front/rear inflation? Thanks, Ron
Ron, you didn't say the brand tires. To my knowledge all major brands except Michelin have the same info for load & inflation and Michelin is same on maybe 95% and those that differ may only differ by 5 psi or so.

Since you only have total for an axle and do not know the heavy side we estimate one side at 53% -- So Front would be 6,042 and rear 8777 (4,389 per tire).

Most 295/75R22.5 LR-G need 110 to support 6,175 F (single) and 80 psi to support 4,540 in Dual.

Since I recommend a +10% of air for a good margin, that would suggest 121 psi front and 88 for the rear. BUT a LR-G is only rated for 110 psi so you need LR-H on the front. Also need to confirm the front wheels are rated for 120 psi and since even H are only rated for 120 that makes the recommended Front inflation 120 psi.

Clearly the estimate of 53% is causing the problem so it increases the need for you to learn the actual side to side load on the tires by going somewhere other than CAT truck stop scale.

It is CAT policy to not do one side weights and that is why they are making it harder to only get one side on the scale.

I suggest RVSEF


Locations with scales
SmartWeigh is another option

I checked around home and found a local building supply that had a scale that would give me 4 weights for $10. Only about 3 mi off I76 just East of Akron OH.



  1. We have weighed on CAT scales but finding one that allows for side weights can be difficult. It must be one with a wide enough apron and no posts that block access. They do exist. Next is convincing the weighmaster to allow you to do it. I tell them to just write "NOT A CERTIFIED WEIGHT" across the weigh ticket to remove them from any responsibility for guaranteeing exact weight - it is not possible to get an exact weight if part of the object to be weighed is supported by a surface other than the scale - laws of physics do apply. We can get approximate weights. There is no possible way to be 100% accurate no matter what device is used or who does the weighing if any part of the object being weight is supported in any other way than completely on the one and only one scale.

  2. You are correct about scale accuracy. Remember we are not weighing to be able to present a weigh slip to some legal authority but to have a basis for inflating a tire. +/- 1% is good enough for our purposes


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