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-   -   Tire pressure? (http://www.airforums.com/forums/f438/tire-pressure-34125.html)

millvalleyca 07-11-2007 11:47 AM

Tire pressure?
 
Hi guys and gals
What's the desired tire pressure for my 2007 25 foot CCD SS? When we picked up our trailer the service tech said he filled the tires at 80% of the recommended pressure. "You'll have a much better ride" was his reasoning.
Thanks in advance for your suggestions.

Wayne&Sam 07-11-2007 12:09 PM

Wiser folks than I will answer this, but I always run my tires at 65psi, the max rating called for by Airstream. I don't find any problem with the ride, and I think the higher pressure provides for less rolling resistance and therefore better mileage.

ScottW 07-11-2007 12:11 PM

I, and almost everyone I know, inflate the tires to the maximum indicated on the sidewall (max cold tire inflation). While providing a 'softer ride' underinflation leads to early tread wear, higher operating temperatures, and...duh...tire failure. Please stick with the max operating pressure.

millvalleyca 07-11-2007 12:21 PM

Works for me!
Thanks for the info.

bobkelly 07-11-2007 12:25 PM

Ditto to Scott's comments---Read your tire sidewall for pressure required to have max tire capacity to carry load. Set this pressure when the tire has not been running (cold temp) and don't worry about ride considerations. Those are very secondary to the primary function of the tire to operate effectively when loaded.

Minnie's Mate 07-11-2007 12:27 PM

This is an often discussed issue here on the forums. The general answer is to put the maximum pressure that your tires are rated for. This is particularly important if you plan on towing at "highway" speeds. I see that you live in California and IIRC, the max towing speed allowed on the interstates in CA is 55 MPH. If that is still the speed limit for trailers, 80% is probably safe. If you plan on towing outside of CA and at speeds above 55 MPH, say at 65 or 70 MPH on the western interstates, you will want to increase the tire pressure.

The faster you tow, the faster the tire walls flex as they go from the curved profile to the flat part that comes into contact with the pavement. This flexing creates friction in the tire wall and generates heat. Heat is the enemy of tire walls and is one of the main culprits in blow-outs. By increasing the tire pressure you stiffen the side walls and reduce the amount of flexing and reduce the amount of heat build up in the side walls of the tires and, thus, reduce the likelihood of a blow-out. It is important to note that this is not the only cause of blow-outs and won't guarantee that you won't have one. It is just a precaution to help reduce the risk.

Yes, your trailer will ride softer and easier if the tire pressure is lower, but I think risk just isn't worth it. My tires are the Goodyear Marathons that came on my Airstream. They have a maximum rating of 65 psi for speeds up to 65 MPH. I currently run 65 psi in them. That is the maximum that my local tire shop was comfortable putting in them. Having said that, Goodyear's web site says that if you want to tow at a higher speed, you can increase the tire pressure to 75 psi and tow at speeds up to 75 MPH. One of our forum members recently replaced all four of his tires with a different brand that recommended 80 psi. It really depends on the manufacturer and their recommendations. The max tire pressure is always embossed on the side of the tire wall near the rim along with the tire's model numbers.

Nearly all of my towing is done on the interstate and in Georgia you either stick to 70-75 minimum or you become a road hazard. Additionally, because the semis stay mostly in the far right hand lane on the interstate, that lane is pretty rough on all Georgia and Florida interstates so I tend to stay in the second from the right lane so my Airstream gets a smoother riding lane. I stop approximately every 2-1/2 to 3 hours for food, fuel, or pottie breaks and I test the temperature of my tires' side walls as soon as we stop. This also gives the tires a chance to cool off some, too, while we are stopped. My wife gets a little impatient with me doing this but I think it is too important to ignore. The first year I just felt of the tires with my hand and they never felt as warm as straight hot tap water. Usually more like a warm bath. I knew this was no accurate way to judge the tire temp so I bought an infrared thermometer from Sears for about $80.

Last week while traveling to central Florida in the heat of June/July my average side wall temperature was about 120F on the shady side and about 130F or so on the sunny side. This averaged about 10F less than the temperature of the truck tires. I also had a 1,000 LBS golf cart in the bed of the truck so it was carrying a heavier load than it normally would so I figured the tire temp on the trailer was in a safe zone. I did happen to take a reading just before we left one rest area and on the sunny side the tire wall temp was 171F after sitting idle in the sun. To make sure it was just the intense Florida sun beating down on the black rubber, I took a temp reading from the shaded treads on the same tire and the temp of the surface of the tire that came in contact with the pavement was 141F in the shade.

This is just my experience and you will get a dozen or more folks that disagree with everything I have written and they are probably more right than I am. I have only towed last year and this year with probably about 9,000 miles under my belt, but I have had no blow-outs and my tire shop said I have about 1/2 of the tread life left in my tires so I guess I'm doing OK. I may have blow-outs on my next trip. Who knows?

Tom Nugler 07-11-2007 01:11 PM

I'm assuming you searched "tire pressure" and the results made your head spin.:huh: Mine did the first time too.
One of of the most interesting was a comment from a Michelin tire engineer claiming that a properly inflated tire should raise no more than 5% in pressure over cold when checked hot. This worked out to 60 psi in the GT.
Also found this Goodyear chart. You'll need to compare load weight to tire size, ect. ect.
The only problem I have found from experience, and may only apply to a lightly loaded, single axle vintage is that the the brakes are more likely to lock up and skid the tires. Usually at the time you need the most traction. Need to pay more attention to the controller I guess.:rolleyes:

Tom.

HowieE 07-11-2007 02:12 PM

Tire pressure is not a hard thing once you have found the manufactures inflation chart. Here is the chart for Goodyear 225 75 R 15
http://www.goodyear.com/rv/pdf/rv_inflation.pdf
While it is generaly accepted that a given tire size, independent of manufacture, would carry the same pressure per load it is a good thing to get the manufactures chart to be sure. Don't expect the tire store to have the answer as most of them have never heard of an inflation chart.

Every manufacture has this chart published for thier tires and you are well advised to use it.

With my tri axle I inflate to 45 lbs. ,not the 65 as noted as the MAX. on the tire sidewall. If I inflated to 65 lbs. the rivets would be flying of the walls and I would have little or no control over the trailer in rain as the trailer would be riding up on ball bearings.

millvalleyca 07-11-2007 03:45 PM

Now I'm back where I started! :sad:
45 and not 65 as stated on the tire HowieE?
80% inflated doesn't seem that bad then.
I was going to go out and buy an air compressor tonight to fill up my tires.
Now I'm gonna have to read a couple of more suggestions :lol:
It sure is tough when you're a newbie who knows nothing about cars/trucks and trailers.
Thanks for the info

LI Pets 07-11-2007 04:14 PM

let's take the 80% issue out of the picture that was a dumb statement by the dealer, you mean he figured 80% of what?

How much air is really in the tire?

What is the max psi stamped on the tire?

What is the max load stamped on the tire?

Last what is the GVW of the trailer on the metal tag either on the side or front of the trailer

Until we know that no one can tell you 100% what tire pressure is correct.

Also what speed do you think you'll travel?

If you plan on doing upto 75mph you need to add 10psi to the total from a chart.

Wasn't that simple, nice thing is you only need to do this jazz once.

AirConditioner 07-11-2007 04:15 PM

Temperature rise really changes inflation pressures. Inflation standards still are a great question. I thought I really had this covered as well until on my last trip out two weeks ago. I stated out at exact 45psi recommended pressure on a cool morning. I checked the pressure 50 miles out in sunny weather and was surprised to find +55psi. This has changed my approach to inflation and on-the-road adjustment.

2airishuman 07-11-2007 04:28 PM

Quote:

Originally Posted by millvalleyca
Now I'm back where I started! :sad:
45 and not 65 as stated on the tire HowieE?

yes u r back at the begining...

which is 2 SEARCH some of the 100s of posts on this topic...

it has all been said b4 and in clearer terms i suspect.

here is JUST ONE...

http://www.airforums.com/forums/f438...ict-19865.html

does your trailer weight the same thing as howieEs unit?

his running at 45psi is foolish UNLESS he's weighed the trailer and knows 45psi fits with the inflation/load tables...

have you weighed the unit yet millva' ?

'load appropriate' inflation is only safe if...
-you know how much the thing weights
-you keep on top of inflation pressures with frequent checks
-you travel at modest speeds.

it's been written many times..

THE SINGLE MOST COMMON CAUSE OF TIRE FAILURE IS UNDER INFLATION.

for the average user the safest thing to do is inflate to max/sidewall pressure listings.

and check pressures before each trip.

so millvalley either get really 'into it' or follow the safest approach and use max psi...

lastly...

Quote:

Originally Posted by HowieE
and I would have little or no control over the trailer in rain as the trailer would be riding up on ball bearings.

this is another common belief that is patently incorrect.

grip is derived from a combination of parameters, like rubber compound, side wall flex, aspect ratio, contact patch and so on.

lowering pressure doesn't INCREASE grip, especially in wet conditions...

lowering pressure enough to enlarge the contact patch REDUCES grip in several ways and may cause the tire to hydroplane...

control in cross winds, semi bow waves and with BRAKING are all negatively affected by lowering tire air pressure.

in theory 'grip' from a pnuematic tire is simply R*mu,
where mu is the co-efficient of friction 4 the tire &
R the reaction force between the tire and ground.

ribs, water channels, and side wall affect reaction forces and are all important for wet/snow handling.

in the simplest terms...

most tires have an "optimum contact patch"
that 'pushes' the rubber compound into the road surface...
lowering pressure enough to enlarge the contact patch DECREASES the push into the roadway.
so 'grip' per area is reduced....


cheers
2air'

silverback 07-11-2007 04:37 PM

Never trust anyone who says it will ride better with less then the specified PSI. Most new Airstreams with dual axles use Goodyear Marathon tires. I believe I read in my Airstream manual to keep them at 65 PSI. I usually set them early in the morning when cool (which is 80+ in Arizona right now). Get yourself a good tire gauge and remember it is worse to under inflate (builds up heat) then it is to slightly over inflate (harsher ride, more wear).
-KL

Cracker 07-11-2007 04:38 PM

Quote:

Originally Posted by HowieE
Tire pressure is not a hard thing once you have found the manufactures inflation chart. Here is the chart for Goodyear 225 75 R 15
http://www.goodyear.com/rv/pdf/rv_inflation.pdf
While it is generaly accepted that a given tire size, independent of manufacture, would carry the same pressure per load it is a good thing to get the manufactures chart to be sure. Don't expect the tire store to have the answer as most of them have never heard of an inflation chart.

Every manufacture has this chart published for thier tires and you are well advised to use it.

With my tri axle I inflate to 45 lbs. ,not the 65 as noted as the MAX. on the tire sidewall. If I inflated to 65 lbs. the rivets would be flying of the walls and I would have little or no control over the trailer in rain as the trailer would be riding up on ball bearings.

I couldn't agree more! Weigh the trailer and inflate the tires accordingly - which, incidentally, for the 2000 30' Excella, complies very nicely with Airstream's recommendation of 50 psi (---which was originally based on using load range "D" tires. I recently switched to load range "E" tires, due to lack of availability of the "D's," however, I still run at 50 psi. As for my truck, if I inflated the rear duallies to their maximum pressure I might just as well throw the tires away and ride on the rims! By actual scale weight determination, I run the duallies at 50 psi running solo and 55 psi with the trailer in tow. I run the front tires at 65 psi, again determined by scale weight. A single rear tire still has more than ample capacity to sustain a blowout on the other tire. I could go lower than 50 psi, however Goodyear recommends a minimum inflation of 45 psi. With over 55,000 miles on the truck (---and the rear set of tires) the duals demonstrate almost a perfect wear pattern. I've only recently (---this summer) switched to a special set of front tires, that Goodyear just came out with, in order to prevent the known "scalping" problem with the dually that has already cost me two sets of front tires. The tires are expensive (over $250 each) but so far I'm very pleased with their performance. I discussed this elsewhere in another topic.


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