Tires: correct air pressure

[Clyde9]

From: Easybago  (Original Message)
Sent: 8/7/2006 7:44 PM

I have load range "E" tires all the way around and was wondering what the correct pressure should be. The tire recommendation is 80 psi max when cold, so, should I run that much pressure? I've been running 50 psi, which is what was in them when I got it. The tires are on a 1978, 26' Brave.

Thanks!



From: tatkin
Sent: 8/7/2006 10:26 PM

I don't know ! 

But, I have been running all my tires, RV or not, at like 10% less than the max rating for the last 35 years.   

I think the duals in back, which I really don't get, are a bit of a different game ...

I am sure I and you will be informed here shortly ...



From: denisondc
Sent: 8/8/2006 8:09 AM

If you were carrying the max load per tire (as printed on the sidewall) then the max press. of 80 psi would be the pressure you would want, and it wont hurt anything to run at that all the time. But you dont need to - if your load-per-tire is less. The sidewall will have a listing for the tires as singles (for front axle use) and duals (for rear axle use).
I have 2 load range E 7.50-17s on the front of my Winnie. The sidewall says max 3170 lbs @ 90 psi (single), and max 2780 lbs @ 80 psi (dual). Since I have about 4000 lbs on the front axle, or 2000 lbs per tire, instead of the max wt of 3170, I run them at 75 psi on the front axle. Im sure I could run them at 60 psi just as well.
I would run them at 65 psi on the rear axle as duals. My rear axle wt load is about 6000 lbs, or 1500 lbs per tire. Im sure I could run them at 50 psi as well. These tires are 'Armour' brand. The DOT tire code tells me they were made in 1998 by the Jiang Su Tyre Factory in Xuzhou, a suburb of Shanghai. They show no weather checking yet.
My best set of tires were by Cooper Tire Co, bought in 1991 and lasted 14 years, till the tread was worn down to the wear indicators. They were load range D, and their sidewalls said 2900 lbs max wt @ 75 psi (single) and 2460 lbs max wt @ 65 (dual). I ran them at 55 or 60 psi for the entire 40,000 miles

All of my weights per tire above were for the empty Winnie, at 10,000 lbs. Fully loaded for a vacation it probably weighed close to 11,000. The GVWR is 13,000. Sometimes we pull a car behind it on a tow dolly, which doesnt add any weight to the motor home itself.

With the air pressures listed above, my tires all run at the same temperature. On a trip I check the temperatures with my hand each time we stop. The sunny side will be -slightly- warmer than the shady side. In no case have my tires ever gotten too warm for me to comfortably hold my hand on them. On a warm sunny day a tire lying out in the sun will be hotter than my tires have ever gotten from traveling on the highway.



From: Easybago
Sent: 8/8/2006 1:45 PM

Thanks Dave, that's what I was looking for. I think I'll try pumping mine up to around 65-70 psi and see how she does.

Preciate it!



From: Easybago
Sent: 8/13/2006 10:36 PM

What a dummy I am! I thought I had Yokohama, load range "E" tires all the way around, but I actually have four Marshall, load range "F" tires on the rear and the Yokohama's on the front. The Marshall tire's maximum pressure is listed at 105 psi, so, I went from 50 psi to 80 psi on the rears and from 50 psi to 70 psi on the fronts.

Annabelle tracks and handles so much better now. I really doubted actually feeling the difference, but I did! She is so much more stable and responsive in turns now, without that "sliding roll" type of feeling. Now maybe my MPG will increase because it felt like I didn't have to keep as much foot in the pedal to keep her at a steady 65 mph.

WooHoo...I can't hardly wait for next weekend's trip!



From: Coachmen1972
Sent: 8/14/2006 11:43 AM

My tires also say 80 max, and are rated E. However, I found a "max tire pressure 60psi" stamped in the split rims.......


From: Cooneytoones
Sent: 8/14/2006 11:18 PM

Good Point......You should never exceed the max rim pressure...especially on split rims....and most of our rims are different from the rims that are produced today. Most of the rims were produced for Bias tires until '77.

Tires that were made back in the 70's when these rigs were new were a little different than the tires out on the market today. Different rubber compounds and polymers are used today that were not available 30 years ago...

As far as your tire pressure...rule of thumb from most vehicle manufacturers is  you should always have more pressure in the front tires than in the rear tires......This is due to several factors of load balance, handling and the way the roads are arched. 2 to 5psi for a car and about 5 to 10psi for a large vehicle running duals in the rear.
(both my buses a Ford and International call for 100 front and 90 rear....)

The inside rear tires take most of the beating...this is why you see so many shredded truck tires on the interstate...( low pressure) The inside tire is actually carrying about 65 to 80% of the load at certain times due to the arching of the road for rain run off, and if you run your pressure too low, heat builds up and will shared the outer cap right off...or just blow the tire to smithereens. Hence the problem with the Ford Explorer's several years back..that was also partly blamed on Firestone...but later was found..it was not the tire, it was the amount of air pressure in the tire....  rear tires being a little softer will give you better tire wear and handling, not to mention the steer tires (front) need to be able the roll without too much resistance, (for better gas mileage, steering and braking) and the rear should have enough of a footprint to push the vehicle forward....You will build up about 5 to 10 psi when the tires reach there operating temp when they start out at the correct cold temp....If you start out too low of a cold psi, the pressure will build up due to the fact that more rubber is being rolled around loosely in the sidewalls and you could build up 60 to 90 psi more, causing catastrophic tire failure...and not only is this bad for handling.....it will wreak havoc with the body panels. 
\
I have 10 x 19.5 radials load range E....they are rated for 120 psi.....my rims (tubeless not split rims) are rated not to exceed 100 psi (and that is cold tire pressure)
I run 90 to 95 lbs in the front depending on the load,
and 85 to 90 in the rear duals.
Always keeping about a 5 lb difference between the front and the back.

Timmy



From: Easybago
Sent: 8/14/2006 11:31 PM

Interesting info! So, with my tires being different load ranges(E on front and F on rear), should I be ok at the pressures I have listed? Even though I have more pressure in the fronts, I'm at 88% of the maximum rated pressure and only 76% of the maximum rated pressure in the rears. Too complicated for my feeble mind!



From: ClydesdaleKevin
Sent: 8/16/2006 1:28 PM


I have 1 year old STA tires on the Ark, and I keep them all at 70psi, front and back...due to the fact that I carry so much weight in the back what with the holding tanks and whatnot.  Max psi on my tires I believe is 80, so I keep it at 70, high enough, but not super high.

One VERY good reason to keep your tires inflated to almost maximum is gas mileage!  It does make a difference!  In the bicycling world, bike tires on racing bikes are kept inflated to 120 psi plus...why?  They call it "rolling resistance."  The softer the tire, the more work it takes to push against the resistance of the tire rolling on the asphalt.  The same applies to cars, trucks, and our RVs.  You get better traction with softer tires, but much better fuel economy with higher pressures...the wheels roll easier on the pavement.  It may seem negligible, but test it yourself:  Hop on a bicycle, air down the tires until they are squishy, and try to ride up a hill.  Next, inflate the tires to max, and try the same hill....MUCH easier, less work!  Less work translates to less work for you engine, which translates to less gas used to complete the same task.

Now, the Ark doesn't get GREAT gas mileage, but its acceptable:  9.2 miles per gallon fully loaded, without towing the van.  Towing the van only drops gas mileage to 8.7 miles per gallon, and I also keep the van tires inflated to maximum.  We tow a full size 1985 Dodge Ram, with a 318 and 727 tranny, and we load it up like a trailer when we travel...and it still barely effects our gas mileage.

Kev