Figuring the correct tire pressure

[two_travelers]

Recently had our coach weighed. We are at 6,700 lbs (3350 per tire) front and 12,180 lbs (3350 per tire) rear when fully loaded. Tires are Goodyear G670. Using the tire pressure chart from Goodyear it would appear that 80 lbs psi is what we want. At that inflation, the steer axle weight is 3640 lbs and rear at 3415 lbs. Tire inflation chart on coach shows 92 lbs psi. It rides like its on hard rubber tires. Should I use the 80psi or bump it up a few lbs? Thanks to all who share their knowledge!!

[Jim_Norman]

I'll second that! NEVER GO BELOW THE MINIMUM. A tire needs a certain inflation to maintain its integrity.

[Dale_Traveling]

Go with the what Goodyear recommends but also add a few PSI to compensate for potential increases in loading or temperature changes.

The coach chart is based on the listed size and load class of the tires that were installed by the chassis builder. If the tires you have now does not match what is listed the chart numbers should not be used.

If you cross reference the chart numbers you'll find the pressure listed for the tire listed will be slightly over the axle maximum capacity. In other words the chart is the pressure for the tires listed if you load the coach to the axle maximum. If your current weight is less than chassis maximum that would be the reason why the pressures don't match and why your ride is rather harsh.

Also if you're off the bottom of the chart, as I am, don't try and extrapolate what the pressure could be. Best to stay at or above the minimum pressure listed on the OEM chart.

[Ductape]

Your analysis is correct. As always you'll get a bunch of wildly conflicting opinions on the internet. Trust Goodyear, they do this for a living.

[Jim_Norman]

Just right is what you really want, however it is difficult to obtain. You need a 4 corner weigh, then set your pressures to the heavier corner for the front and for the rear. Under inflation is a killer, in many ways. Tires overheat, sidewalls flex way beyond design, handling downgrades and ride can worsen. Now over inflating has its own issues, hard ride, odd tread wear among others.

So get weighed with your rig as full as you use it, not empty. Get each corner weighed and then do the research. And when you are done, remember tire pressure is not a constant! Monitor it! If you inflate in June, you will not be correct in December! Check you tire pressure each trip, or possibly get a TPMS system and set it up. It could save more than a flat tire.

[wildmanbaker]

theoldwizard1 wrote:
What is the maximum on the sidewall ?

I would use that. Less rolling resistance (might help fuel economy). Less sidewall flex (reduces heat and stress on the tire).

Yes, don't trade comfort for safety. If you have tried the manufacture's recommendations and don't like it try 5 psi more to see of the drive is better. Low tire pressure, flexing, and heat buildup are killers for the tires.

[theoldwizard1]

What is the maximum on the sidewall ?

I would use that. Less rolling resistance (might help fuel economy). Less sidewall flex (reduces heat and stress on the tire).

[dalenoel]

At the 80psi inflation you are able to handle more weight than what the axle actually has. What you don't know is if the weight on the curb side is the same as the street side. The best route is to weight each corner and use the heaviest weight for each side of the axle as the weight for both tires on that axle.

Since you don't know the actual 4 corner weight your estimate is better in having more weight carrying capacity that the actual average. In other words 7280 for the front axle and 13660 for the rear axle. This does give you a little margin for some error in calculation.

Less pressure will, or should, give you a little better ride but you don't want to go too low until you know the heaviest corner and end up under the recommended pressure.

[wildtoad]

Set them at 80 and see if you like the ride. Based on your info 80 will support more than you weigh.

[Effy]

Confused, are you saying that after you set the PSI, you weighed it again and the weight per wheel changed? You claim your weight in the front increased almost 300 per wheel and 65 in the rear. So your MH gained weight??? I am lost.