Tire pressure confusion

roadrat57 wrote:
The numbers on the vehicle chart show GAVW 7000 front and GAVW 13500 rear. Goodyear bold numbers show 95 psi with front 4080-3970 pounds. ??

With a front axle load weight of 7000, 3500 per tire is probably not an accurate weight for each tire. Depending on rig and loading it could be for example 4000 pounds on one side and 3000 pounds on the other. This is why individual tire load weight is important if you can get it.

Also ALL tires on the same axle need to be at the same pressure. Inflate both to the pressure required for the heavier load.

Somewhat over inflated is better (safer) than under inflated. I had a Michelin rep tell us that a tire run 10 pounds under inflated for any distance should be considered to have been run flat.

Check tread depth across the width of the tires once in while. More tread wear in the centre the tire shows over inflation. Faster wear on BOTH edges indicates under inflation and wear only on one side of a tire indicates a possible alignment problem. There are other tread wear conditions that can show other problems; get the tires inspected by a knowledgeable tire expert.

On a similar theme, we were advised to over inflate the tires of the tow car when towing (at least for long trips) to minimise outer edge tread wear on the front tires caused by side slip while cornering.

We tow for at least 11,000 kilometers per year.

Note finally that once a wear pattern starts it cannot be reversed. Proper inflation and tire rotation can halt the uneven wear but will not reverse it.

As has been stated, get your coach weighed as you would normally travel....with clothes, people, food, beverage, on-board water, tools, chairs, propane tank(s), etc.....whatever you would travel with....(minimum of each axle..preferably each corner). Look a the tire manufacturer's pressure chart, inflate to that number when the tires are cold and you'll be fine.

MAX COLD PRESSURE indicated on the tire sidewall is the maximum safe pressure that the engineers for the manufacturer decided upon when they designed the tire. That means that the tire can safely be inflated to that pressure when the tire is cold and the normal increase in pressure from driving will not hurt it.

What does COLD mean? It means the tire and the air inside is at the ambient temperature and has not been driven on or stored in a heated place. If it is 98 degrees outside and you haven't driven anywhere (IE., morning of your trip), you can safely inflate the tire to the rated MAX COLD PRESSURE stamped on the tire. If it is 20 degrees outside and you haven't driven anywhere (IE., the morning of your trip), you can safely inflate the tire to the rated MAX COLD PRESSURE stamped on the tire. BUT...you'd be better off to inflate according to the recommended pressure for the weight of your LOADED coach.

And as for recommendations? Inflate to the tire pressure chart recommendations according to the weight you have on-board....sounds like a broken record, right?

Best bet is to make sure you aren't UNDER-inflated......

On our unit we have the tires set at 80 psi front and rear. This was based on having the unit weighted front and rear at a rally. We have a front axle rated at 7000 lbs and rear axle rated at 12000 lbs. Gross 18,000 lbs.

Ford recommends 82 lbs front and rear. Goodyear based on weights was 78-80 lbs the higher the pressure the harder the ride.

Per the tire pressure system the tire pressure seems to gain between 8-15 lbs depending on outside temperature. I set the tire pressure when the outside temperature were in the 70-75 range. When it is cold out they read slightly lower but within 10 miles they are right on the money. This also allows for the hot tire pressures to be within Goodyear's recommended max pressure.

Thank you Wildtoad! Now that makes sense.

roadrat57 wrote:
I guess if I weighed my rig every time I traveled I could get the perfect psi. I am not looking for the perfect psi. How about an average psi for an average weight load?

The idea is not to weigh it every time, just once you have it loaded with your usual stuff, water, full tank of gas, propane. I myself just use the GAWR and move on which gives me the piece of mind. I try not to over think things.

The 7000 for the front axle translates to 3500 per tire so you can use the 82 that CW set them to. The 13500 translates to 3375 per tire so the 82 works also. The chart says 80 will be fine for all tires. In both cases you weights are below the minimum pressure listed (80) needed to support the weight. Like I said ignore the sidewall number and the numbers in bold on the chart as you will never need them.

I would use the 82 as it gives a bit of a cushion in case you are overweight.

I guess if I weighed my rig every time I traveled I could get the perfect psi. I am not looking for the perfect psi. How about an average psi for an average weight load?

The numbers on the vehicle chart show GAVW 7000 front and GAVW 13500 rear. Goodyear bold numbers show 95 psi with front 4080-3970 pounds. ??

You are looking at the worst case numbers. The number on the side of the tire is for the most part a meaningless number, as is the bold number on the Goodyear chart. As mentioned above at a minimum we would need the axle weight ratings (front and rear) to give you a better number. Best yet are actual weights as you use the unit. The placard in the mh should provide the maximum weights each axle can carry. Give us those numbers.

FYI the weights provided by my mh manufacturer and those from Ford were the same. But they both disagreed with the numbers from Goodyear.

In other words... you need to weight your rv, preferably at each corner...lacking that.... at least by each axel. Then go to the Goodyear tire/pressure chart.

Ron