2017 bighorn fb. full timing, trying figure out about how much wt on each tire for air press and if I need to upgrade to 17.5 tires. already have upgraded 8000 axles and brakes
Hi Kathi,
Until you have an opportunity to get actual individual wheel weights, all you can do is estimate and leave yourself a safety margin. On most rigs, if you assume 20% of the Gross Vehicle Weight Rating (GVWR) rests on the hitch, the remaining 80% sits on the wheels.
So if you have a coach with GVWR of 16,000, that would be about 3,200 lbs on the hitch and about 12,800 lbs on the wheels. That's about 3,200 lbs on each wheel, if you assume the weight is evenly distributed.
Let's stay with that assumption for a moment. 16" Load Range G tires like the Goodyear G614 and Sailun S637 have a load rating of 3,750 lbs when inflated to 110 psi. So that would give you a 550 lbs safety margin. That's about a 17% safety margin (550/3,200).
That's a number of assumptions. 1) You're not overloaded, weighing more than GVWR. 2) 20% of the GVWR is on the hitch. 3) The remaining weight is evenly distributed on the 4 wheels.
The big problem is even distribution. It never is even. The first time I had individual wheel weights done, one wheel weighed 2,500. Another weighed 3,450. The heavy wheel had a 6% safety margin which could easily be consumed by losing a little air pressure.
To provide a 20% safety margin on the one wheel weighing in at 3,450, I would need a tire with load capacity of 4,130 lbs.
Since then I've rebalanced loads inside the coach and at a weigh-in 2 years later, all wheels were running between 3,000 and 3,200. With those weights, I could have stayed with 16" Goodyear G614 tires and had about 17% safety margin, as long as I continued to manage weight distribution.
Instead, at 4 years/40,000 miles I replaced the wheels and tires with 17.5" Goodyear G114 tires. At 105 psi, I now have a load capacity of 4,180 lbs on each wheel, which gives me more than a 25% safety margin.
Hope this helps.