Tire Load Math - A Second Opinion?

[KathyandDave]

The point of this topic is to get a second opinion of my calculations (and third and fourth...after all, this IS the MOC). I hope to learn from the discussion, especially from the old hands in the tire business.
The door sticker ratings for the TV (in lbs.) are: front = 4800, rear = 8200. Yes, the gross is less than the sum of these two, but I'll keep that in mind in the real world. The tires are LT215/85R16E all around. Duallies in the rear. Assume that I want to fully load the axles. Using the Goodyear and Michelin inflation charts, I get that the front tires should be inflated to 70lbs. and the rear tires to 65lbs. What would you get?

[LonnieB]

Your calculations are good, with the weights stated. Have you actually weighed the truck?
What does the sticker on the door post list for front and rear psi?

[KathyandDave]

I have weighed the TV several times with the gang on board and the Monty in tow, usually by driving over unattended provincial weigh scales. A couple of times, we've been overweight by a few pounds on the front axle (up to 50lbs. over, usually under by about the same amount). It's easy to do - a great deal on firewood along the way, for example. So, the actual front weight is about the rated value. The rear runs less than maximum by a wide margin. At its heaviest, it weighed 7200lbs. I calculate that the duallies should be inflated to 55lbs. for that load. Do you agree?

The door sticker shows the the same maximum pressures as I calculated (thanks, LonnieB, for pointing that out - now I feel a bit dumb!)

One lesson learned - the oversize diesel tank weighs a lot and spreads the load between front and rear axles. Diesel weighs about 1.93 lbs. per litre x 211 litres = 407lbs! The tank is on the driver's side and tilts the truck a bit to the left.

[KathyandDave]

Another lesson learned...check everything yourself. I just had the tires rotated at the GM dealer. I set out to check, then adjust the pressures according to the discussion on this thread. They had inflated the duallies to 75lbs and the front tires to 60lbs!

[TLightning]

quote:Originally posted by KathyandDave

The door sticker ratings for the TV (in lbs.) are: front = 4800, rear = 8200. Yes, the gross is less than the sum of these two, but I'll keep that in mind in the real world.

The gross is always less the sum of the two axles. This allows us to be flexible when loading...one time you might need extra capacity in the rear, so you load the front lightly...next time might be vice versa.

[sreigle]

The 70 psi is what you need to have in the tires to support the load adequately without damage to the tires or excessive wear. In my opinion, bumping that up to 80, the tire max, is not enough increase to hurt the tire wear and provides an extra margin in case a tire loses a little air (not going flat, just losing a little air). It also accommodates pressure changes due to outside temperature changes and altitude changes. I run 80 in the rears when towing and drop the psi when towing. I leave the front tire psi the same all the time since hitching up changes weight on the front tires by only an insignificant amount (maybe 10 pounds in our case). This is just how I do it. It's worked well for us. Our last set of tires, BFG Rugged Trail T/A, got 70,000 miles with another 5 to 7 thousand remaining when I bought new tires. So we must be doing it right. Or at least not wrong.

[KathyandDave]

After setting the pressures according to the chart(s), we just ran for four full days of driving over roads of various quality. The ride quality and handling was vastly improved.

[richfaa]

I am so confused.... The tag on my door says..Front 6K, 75psi cold( truck has the snow plow package)

Rear (dually) 9K, 60psi cold(truck has the camper package) I assumed that the 75psi cold on the front meant that would be the psi required IF I had 6K on the front axle.The 60psi cold was the psi required IF I had 9K on the rear axle. I do not have have a snow plow on the front axle and although the diesel motor is heavy there is nowhere near 6K on the front axle. I do not have a camper in the bed although I do have a hitch, some camper stuff and the pin weight of the 3400 but even at max pin weight we do not have 9K on the rear axle. I wanted to get everything weighed at the escapee's rally and use the charts but the bad weather did that in. 75psi is way to hard for the front tires and if we do not have 9K on the rear axle that would mean that 60psi is to hard and should be less.??? none of that computes to me. I have experimented with 80psi in the rear dually's and it was a rough ride. we have 60psi in the front??? and 70 on the rear??? The wear is even and the ride feels good????I am so confused????

[steves]

It's OK to be confused as long as the truck handles well and tire wear is good...."Be happy"

[8e3k0]

We run 75psi on the fronts and 70psi on the rear duallies even though the sticker states 60psi. If they were singles on the back as with the other F 350 we run 80 psi. We do not have the snow plow package but do have the Camper package. Our truck runs with a load in the area of 90 % of the time it is on the road. In my 40 plus years of running trucks for recreation and farm, I have never had a blow out do to uninflation and heat as I always ran on the upper side of the truck and tire ratings, plus rated and checked air pressures at the start of every trip. We have always attained excellent mileage and life out of all the different manufactures tires. I am a believer in keeping that pressure up there, thus reducing any possibility of heat developing. Also gives me that comfort zone when weather is hot and speed is above average. Ellis