Community Forums

wrinkles · 05-08-2014, 01:28 PM

I just replaced all 6 with ah12 Hankook 255/70/r22.5, had unit weighed ft. axel7500# rear 13200# According to hankook inflation table I would only need 80psi and I would still be over by 1000# in front and2000# in rear on the weight carrying capacity. Give me your opinions I know they will run hotter and my millage could be affected, I currently am at 85# all around. Thanks to all.
Wrinkles

Full.Monte · 05-08-2014, 04:32 PM

If you read some of the threads here on tire inflation, there's a guy who was in the tire business. What he said was to find out what the tables say and then add 5 to 10 psi to the recommended air pressure.

ImagineIF · 05-08-2014, 04:47 PM

Never run tire pressure at less than that required for the carrying the most weight, on a per axle basis. Don't run at a pressure less than the lowest pressure on the chart. There is a minimum to keep tires on the wheels. Most manufactures set the low limit to about 80psi. When in doubt, over inflate as long as you don't exceed the tire's maximum rated pressure.

onechaddude · 05-08-2014, 04:49 PM

I think you would rather have them a little over inflated (to a certain extent) than under inflated. If the ride quality is suitable to you I believe I would leave well enough alone.

Chad

Gorlininc · 05-08-2014, 11:29 PM

I have new tires 2 years ago with 30K miles on them now. I always run the PSI that the manufacturer recommends when they designed the rig. My 38 diplomat runs 105 in the front and 115 in the rear. Just what us called for on the plaque in the rig.
My tires are wearing properly and don't overheat. That's my opinion.

broadrun · 05-09-2014, 07:08 AM

Quote:

Originally Posted by Gorlininc

I have new tires 2 years ago with 30K miles on them now. I always run the PSI that the manufacturer recommends when they designed the rig. My 38 diplomat runs 105 in the front and 115 in the rear. Just what us called for on the plaque in the rig.
My tires are wearing properly and don't overheat. That's my opinion.

Same for me. 105 front and 115 rear

Vanwill · 05-09-2014, 10:38 AM

I think there can be a great deal of "anality" about tire pressures matched to the weight they are carrying. I have never read anything on any tire manufacturer's site that would discourage one from running ANY tire at its max rated pressure. But there are always those who will cite all kinds of reasons for not running max pressure, even though ALL the trucking companies do. And if you have noticed, "RV specific" tires are shrinking in variety and supply. They are also always higher priced than comparable truck tires.

I think the only reason for using weights and the tire manufacturer's tables is to determine the minimum SAFE pressure for the tire to carry a particular load. And why would anyone want to know the MINIMUM safe pressure? If there is any reason other than to soften the ride as much as possible, I've never heard it.

There are always posts warning of things apocalyptic if you do not exactly match tire pressure to weight. But all you need be concerned about is that your tires are inflated at AT LEAST what the manufacturer says is the lowest allowable pressure for the load on the tire. If you are a person who is very sensitive to the ride quality of a tire based on its inflation pressure, you would want to do this. I have friends whom I believe are honest when they say they can tell a large difference in ride quality when the pressure is reduced from the max. I have run pressures from the lowest allowable on the weight tables, to the max recommended for the tire. I can tell no appreciable difference. But then, I have ridden motorcycles for long distances all my life, and perhaps I have an "iron butt".

Bottom line is just be sure you are not running your tires under-inflated for the load they are carrying. Running them at a pressure higher than that is not a problem.

Van W 2000 Dynasty 36, pulling one Harley
Eastern NC

Gorlininc · 05-09-2014, 11:17 PM

Agree.
I've noticed some people running less pressure in the rear tires because there are two per side. It's a bad idea. If you get a flat in one tire and all the weight is on the one tire if that side a blow out will occur.
I'm not sure why people think it is that necessary to run tired at such a low pressure. It makes no sense to me.

JDL · 05-10-2014, 07:43 AM

My take is similar. I have weighed my 4 corners and could reduce my air pressure to 80ish PSI according to the max weight I typically carry. However I run 95 PSI, that allows my tires to nearly match the weight carrying capacity of the axles. I have driven it with 125 psi, and there is a difference vs 95.

My placard is invalid on my coach as it came from the factory with 275/75 running 120 or 125 PSI. In 2002 Monaco replaced all the tires to 295/80, however they didn't change the placard. The paperwork for the tire retrofit recommended running 90 PSI.

Once one of the dual tires are gone, the other tire is going to be overloaded regardless of pressure. 315/80s at 125 PSI are still short 1000lbs. on a single load. Keeping all the tires in good shape and inflated will give you a 98% chance of not having to deal with this on the road.

Gordon Dewald · 05-10-2014, 08:02 AM

Quote:

Originally Posted by Vanwill

I think there can be a great deal of "anality" about tire pressures matched to the weight they are carrying. I have never read anything on any tire manufacturer's site that would discourage one from running ANY tire at its max rated pressure. But there are always those who will cite all kinds of reasons for not running max pressure, even though ALL the trucking companies do. And if you have noticed, "RV specific" tires are shrinking in variety and supply. They are also always higher priced than comparable truck tires.

I think the only reason for using weights and the tire manufacturer's tables is to determine the minimum SAFE pressure for the tire to carry a particular load. And why would anyone want to know the MINIMUM safe pressure? If there is any reason other than to soften the ride as much as possible, I've never heard it.

There are always posts warning of things apocalyptic if you do not exactly match tire pressure to weight. But all you need be concerned about is that your tires are inflated at AT LEAST what the manufacturer says is the lowest allowable pressure for the load on the tire. If you are a person who is very sensitive to the ride quality of a tire based on its inflation pressure, you would want to do this. I have friends whom I believe are honest when they say they can tell a large difference in ride quality when the pressure is reduced from the max. I have run pressures from the lowest allowable on the weight tables, to the max recommended for the tire. I can tell no appreciable difference. But then, I have ridden motorcycles for long distances all my life, and perhaps I have an "iron butt".

Bottom line is just be sure you are not running your tires under-inflated for the load they are carrying. Running them at a pressure higher than that is not a problem.

Van W 2000 Dynasty 36, pulling one Harley
Eastern NC

Well said.

If you decide to reduce the tire pressure it is only because you can feel a difference in the ride quality. Tires generally "time" out before they "mile" out on motorhomes so any reduction in tire life due to reduced pressure (above min specs for tire) will be supplemented with a better ride and perhaps less stress on the coach.

I believe that a firmer tire will result in less rolling resistance and better mileage so another factor to consider.

Gorlininc · 05-10-2014, 09:16 AM

Agree with that also. The tire size has a lot to go with how much pressure goes into the tire.
Does anyone have any idea how many miles you can expect from motorhome tires. My Goodyear's are 2012 and I've put 30K on them and I'm on a 8 month trip now. Just curious. There's plenty of tread on these tires.
Another thought is as you are traveling at 65MPH and you hit a hump in the road and porpoise. The weight on the tires increase dramatically for a short period of time.

wa8yxm · 05-10-2014, 10:43 AM

YOu said if you run it at 80 (I gather the chart only goes down to 80) you'd still have more weight carrying ability than you have weight to carry.

I'd go 80 PSI.

Over inflation will not cause tires to run hotter (under will) it will however cause the center of the tread to wear faster than the edges reducing overall tread life, it will give a harder (Rougher) ride and it will reduce handling in other than ideal conditions, not sure about ideal conditions.

Under inflation causes more heat, more sidewall flex SOFTER ride, more wear at the edges on the tire and loss of control under ALL conditions.

stuhly · 05-10-2014, 11:39 AM

Just my .03 cents worth I would run 90 - 95. I bought a gazillion trucks over the years and underinflation ruins more tires than anything.

ImagineIF · 05-10-2014, 05:00 PM

Quote:

Originally Posted by stuhly

Just my .03 cents worth I would run 90 - 95. I bought a gazillion trucks over the years and underinflation ruins more tires than anything.

Agree. A tire that's run 20% below it's required pressure will be ruined. The sidewall can't handle under inflation.

FWIW, I run my steers 20psi over the minimum and still 15psi below the maximum allowed pressure. I did the same on my last coach. After 20K miles the thread ware was even.