Toyo 295/75-22.5 tire pressure

[TJ]

Originally Posted by chefred112

what are you running for tire pressure...

What the Michelin tire chart says for my tire size and corner weight (rounded up to the next weight level); 110 PSI steer, 90 PSI for drive and tag. And, I run an EezTire TPMS to keep an eye on tire temperature and pressure.

TJ

[chefred112]

So I went to a CAT Scale today to at least weigh the axles...front weight is 11780 lbs and rear is 18720 lbs for a total of 30500 total weight. GVWR is 32700 lbs. This is with full fresh water and fuel. I want to estimate how much air to have in tires so if I use the weights as estimates (no time for individual corner weights) the fronts is approximately 5890 lbs and rears is 4680 lbs., based on my tire size I think the pressure for fronts should be 105lbs and rear 85lbs. Am I reading the Toyo chart correctly?

[chefred112]

tire table

[TJ]

Originally Posted by chefred112

So I went to a CAT Scale today to at least weigh the axles...front weight is 11780 lbs and rear is 18720 lbs for a total of 30500 total weight. GVWR is 32700 lbs. This is with full fresh water and fuel. I want to estimate how much air to have in tires so if I use the weights as estimates (no time for individual corner weights) the fronts is approximately 5890 lbs and rears is 4680 lbs., based on my tire size I think the pressure for fronts should be 105lbs and rear 85lbs. Am I reading the Toyo chart correctly?

You are reading the chart correctly, but you may not be using the best data. If you assume a 50% split of the front axle weight, that’s 5,890 pounds per side and falls in the 105 PSI range on the chart, as you note. Side-to-side loading is rarely 50-50, however, and that’s why using 55% of the axle weight to establish estimated corner weights is recommended. It is not unusual to find a side-to-side weight difference of several hundred pounds.

Using the 55% calculation results in a front corner weight of 6,479 pounds on your coach. That appears to put you beyond the maximum weight rating for that size tire since 110 PSI is the last table entry on the chart and it only supports 6,175 pounds.

This is why it is so important to get actual corner weights. I know that can sometimes be difficult to accomplish, but I believe that safety trumps inconvenience. Am I saying that your coach steer axle is overloaded? I don’t know. And, the reason I don’t know is that I don’t have any hard data to base an informed decision on. It would appear to me, however, that your tires might be on the edge of overloaded on the front axle, even at 110 PSI. That is not a place where I would want to be. Maybe shifting some weight toward the rear might be possible to provide more of a safety cushion.

It would appear from a quick look at your drive axle weight that 85 PSI is correct if you assume a 50-50 side-to-side weight distribution and 100 PSI would meet the 55% calculation.

TJ