Desert tire pressure July 19, 2003, 10:15:08 am Yahoo Message Number: 24710Tire pressures are set cold, but pressure specifications of course assume a heat rise and a pressure rise once travel begins. One way to determine if you have the correct pressure is by the pressure rise as the tire warms. Auto racers often determine correct pressue for prevailing conditions by pressure rise, not by either cold or warm inflation per se. I believe that for automobile tires the pressure rise should be about 4 pounds. I believe the normal assumption is that if it is lower you're over-inflated and if it is higher you're under-inflated. The normal assumption is that under inflation equals more heat due to increased tire flexing during rotation, just like when you repeatedly bend a piece of metal to break it. For future reference, you could check this for your LD on a normal day. Set the tires to the cold pressure recommended in the LD manual. Go for a good long freeway drive at the warmest part of the day and then check the pressures warm. Assuming you had the proper pressure set to begin with, you've now determined the normal pressure rise for your tires and the warm inflation pressure that was presumably intended by the cold inflation pressures specified in the manual. If you're worried about excessive pressure rise in a hot desert environment, set the proper cold inflation pressure in the morning and then check the warm pressure after sufficient driving to fully warm the tires and perhaps again later if the temperature outside continues to rise. If you're over what you've previously measured as your hot inflation pressure then bleed off some air to the proper level if you want. But I'd check again later to see if the warm pressure in fact remains on target. If I am correct that the tires supplied on the LD are rated for 80 psi max cold inflation pressure, then according to the LD manual this whole issue should never arise for front tires. At the Gross Axle Weight Rating of 4600 pounds, which of course should not be exceeded, the recommended cold inflation pressure is 65 pounds. So this is a rear axle issue only. If this concerns you I'd just determine the corresponding warm inflation pressure for your load and keep it there during hot conditions. But far greater risks are overloading the motorhome at one or more corners or being underinflated due to a failure to check inflation prior to travel or simply having cheap, excessively worn or old tires. When you see those side of the road blowouts, I suspect those are the causes. It's not likely someone with a properly loaded vehicle riding on a new set of premium Bridgestones or Michelins set to the proper cold inflation pressure. But if you're worried, determine the proper hot pressure of your tires and keep them there.
Re: Desert tire pressure Reply #1 – July 19, 2003, 04:01:04 pm Yahoo Message Number: 24720QuoteTire pressures are set cold, but pressure specifications of course assume a heat rise Quoteand a pressure rise once travel begins. One way to determine if you have the correctQuotepressure is by the pressure rise as the tire warms. Thank you. This is some interesting input. Would you not agree that the reason they tell the public only to check cold; is that it's the simplest to avoid people goofing up the tire pressure. Lets face it, it's hard enough to get people to keep correct tire pressure, without adding anything to it.QuoteI believe the normal assumption is that if it is lower you're over- inflated and Quoteif it is higher you're under-inflated. The normal assumption is that under inflation Quoteequals more heat due to increased tire flexing during rotation, just like when youQuoterepeatedly bend a piece of metal to break it. From what you've written. I can see you have a good understanding of the engineering. Would you agree, that when a vehicles tires are cold, they are technically underinflated? The engineers are counting on that temp/psi rise. Thus, when I talk about underinflating...I'm only talking about a little...not alot. I'm counting on the temp rise to take care of "underinflation" rather quickly...thus the sidewall movement becomes normal, soon...just like in a properly inflated tire. NOTE! THIS DOES NOT APPLY TO RV TIRES THAT ARE MAX 80PSI AND PROPER INFLATION IS ONLY 65PSI! I'm talking about tires that you're inflating cold near max cold pressure.QuoteIf this concerns you I'd just determine the corresponding warm inflation pressure forQuoteyour load and keep it there during hot conditions. I can see adjusting warm as ideal. Biggest problem is proper understanding of what is going on....thus it opens a pandoras box in getting the public to do this right. It's better just to talk to people about cold temps.Would you not agree that there must be a range of hot pressures the tire will operate in properly? All I have attempted is avoiding overstressing the tire with excessive hot pressure. Personally, I think it would be difficult to keep adjusting hot pressure on the road to stay at a desired psi....not to mention time wasting in stopping often.I can see some here claiming simple physics. When the most basic physics is that when you heat something up, it weakens. Heat it up enough and it becomes liquid. Imagine driving down the road, extremely hot out, psi at max the tire is designed...this tire is extemely stressed...then you hit a small rock in the road that you normally wouln't even notice...what do you think that does to the tire belts? Or you hit a small hole, or ridge, or crack in the pavement...under these conditions, what do you think it's doing to the tire casing/belts?I can see that a 80psi max tire inflated to only 65psi. Even under extreme heat and temperature rise/psi rise. It is designed to take much more. You should only have to worry about proper inflation. I can see with a tire situation such as this...by far...the biggest worry only, is underinflation.But far greater risks areQuoteoverloading the motorhome at one or more corners or being underinflated due to a Quotefailure to check inflation prior to travel or simply having cheap, excessively worn or Quoteold tires. When you see those side of the road blowouts, I suspect those are theQuotecauses. I can see your point here. I am wondering if there are any RV's out there that are using tires inflated to near maximum cold temp? If so, I would worry much more about driving in extreme desert heat with these.With that in mind. I still avoid the extreme desert heat in summer. I hate the thought of breaking down out there.I noticed they are going to require pressure units in vehicles next year. These are units that monitor tire pressure, and send a signal to a box on the dash to give you the pressure. This will make tires much easier to maintain proper pressure. I think it will be interesting to see if the tire manufacturers come out with more info on hot pressures after these units are out? ? ? ? ? ? ? ?RonP
Re: Desert tire pressure Reply #2 – July 19, 2003, 10:43:20 pm Yahoo Message Number: 24737"Would you agree, that when a vehicles tires are cold, they are technically underinflated? The engineers are counting on that temp/psi rise." Not quite. The engineers are *allowing for* that temp/psi rise in the safe operating range of the tire. Cold tires properly inflated are NOT underinflated; they're simply at the lower end of their operating range. "All I have attempted is avoiding overstressing the tire with excessive hot pressure." Here's the problem, Ron: you're focusing on air pressure alone as a cause of failure. It isn't. As I pointed out in my last message, what kills tires is not air pressure per se, but heat and deterioration of the sidewalls. Think of it this way: no tire ever blew out with its carcass intact. ;-) Conversely, if the carcass fails, it doesn't matter whether the air pressure is high, low or in between-- that tire will blow out. You need to stop thinking of air pressure as a cause of failure and start focusing on what underinflation does to damage your tire's body, because thath's where the danger lies. Let's go back to what Terry said, because he hit the nail on the head: "under inflation equals more heat due to increased tire flexing during rotation, just like when you repeatedly bend a piece of metal to break it." That's what causes blowouts. Not hot air, but a damaged sidewall due to flexing and the resulting heat *in the sidewall*. And underinflation causes excess flexing. It's that simple. "I can see some here claiming simple physics. When the most basic physics is that when you heat something up, it weakens." You're exactly right. That's why underinflation is always a bad idea, because it heats and weakens the tire's rubber. When that rubber weakens, you risk a blowout. That's why the article "Gauge Your Chances of a Blowout" in the current issue of the Escapees magazine strongly recommends against underinflation under any circumstances, based on information from NHTSA and the Rubber Manufacturers Association. And that's why the Tire Industry Safety Council recently paid for billboards in Washington, D.C. that read "The only thing worse than inflation is under-inflation." ;-)-- Andy Baird
Desert tire pressure Reply #3 – July 19, 2003, 07:08:47 pm Yahoo Message Number: 24728Hi Terry Am I safe in assuming that when the LD rolls out of the factory, all 4 corners are equally balanced weight wise? So that when I load it, I can just distribute things hopefully pretty equally? Until I can get it weighed? Or should most of the weight be over the rear axel. I wouldn't think there would be any added weight on the front axel(except me).? Are the appliances distributed equally? Should more go on one side or the other? Aaaaaaaaauuurrrrrrrgh! Can I get my money back?Pat (Mac) No Calif. 95 today, 104 yesterday.
Re: [Life With A Lazy Daze RV] Desert tire pressure Reply #4 – July 19, 2003, 09:32:52 pm Yahoo Message Number: 24736Hmmm talk about a pandoras box sheesh...... well lets look at the motor home a little.....[-----O]to be honest if you were to divide the motor home exactly
Re: [Life With A Lazy Daze RV] Desert tire pressure Reply #5 – July 20, 2003, 12:09:19 am Yahoo Message Number: 24746Jim Thanks for the info. Makes sense. Maybe I won't ask for my money back. Hopefully things will all fall in place once Belle (Canto) is delivered.Pat (Mac) 2003 23.5 Front Dinette Sonoma County, Calif
Re: [Life With A Lazy Daze RV] Desert tire pressure Reply #6 – July 20, 2003, 12:54:34 am Yahoo Message Number: 24747Personally I have no problem with people whom wish to drive fast. but there is a reason for 55 as a speed limit for trucka and trailers...I kmpw that its hardly ever followed
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