tireman9

If they were all 36 psi @ 100F I am not surprised that 4 months later at cooler? temp they measures 30. In general tires loose 1% to 3% air each month when temperature compensated in a stationary test in a lab. What was the temp when you measured Oct 1?

Glad you were able to make it to Redmond. Good question with relatively simple naswer. First let me relate my experience. After leaving Redmond I spent a number of weeks in OR, WA, BC AB, Glacier Nat Park & Yellowstone and had a number of days when it was warm followed by snow or frost the next AM. As I mentioned in my Seminar I have two TPM systems on my coach (internal and external) so I can compare the readings for both pressure and temperature. Yes temperature will affect the tire pressure. I have a few posts on Temperature and pressure, including one with all the technical formulas for those so inclined. The rule of thumb is about 2 percent change for every 10°F change. An example would be if you set your cold pressure to 80 psi in Oklahoma City in November and it's 45°F you may see your cold pressure has increased to about 86 psi in Phoenix the next morning when it is 85°F. BUT Operating temperature is really a function of the heat generated by the tire flexing. The upper limit of tire temperature when properly inflated and loaded, is reached when the heat (BTU) flowing out of a tire is equal to the heat being generated by driving. The flow of heat out is faster when the outside air is colder then when it is hotter so there are some complex interactions. I'm not going to put everyone to sleep with the details on heat flow. BOTTOM LINE: When you set the pressure in the morning the tire will partially adjust for the change in outside temperature as outlined in your example so you should not make change when the tire is hot or until the tire has had at least a couple hours to reach ambient temperature. I know this based on my direct observations made during my travels in Aug & Sept. You should still be withing +/- a couple psi of your goal "cold" pressure each morning of a travel day. Remember you establish your goal pressure bu knowing your actual tire loads (corner loads), using your tire mfg Load/Infl tables to learn the MINIMUM cold pressure and then add 10% to the Min. Inflation to get your goal pressure.

I got this question and thought that others might be wondering about the same topic. Jim K asked Subject: tire pressure Message: I will be traveling in the desert for the first time and I am wondering if I should reduce the tire pressure before I go. The hot road will increase the pressure and I am afraid of damaging my tires. ++++++++++++++++++++++ Hi Jim, No you don't have to worry about hot roads. IF you run the correct cold pressure Also you should NOT reduce the cold pressure to "compensate" for the hot roads. Now you didn't say if you have a standard RV trailer or a Motorhome so I will give you the short answer for each application. (FMCA members can share this part with friends with towables) Trailers: You should set the Cold Inflation to the pressure on the tire sidewall. If you look at the sticker on the side of your trailer you should find the tire size, type, Load Range and pressure recommendation from the manufacturer. In almost all cases the recommended inflation is the inflation on the sidewall of the tires. Have you confirmed you are not overloading any of your tires? Simply guessing or looking at the tires is not good enough you need to get the trailer on a scale and at a minimum get the total load on the tires. Now you can't assume the load is equally distributed side to side or axle to axle Measurements of thousands of trailers suggests you need to assume at least 53/47 to 55/45 split axle to axle and split side to side so you need to calculate the heaviest load based on an estimate of 27% to 30% of the total being on one of the 4 tires. A better method is to get individual tire loading. You can learn more HERE. Motorhomes are a bit different than towables. Here you need to get the "corner" loading as the side to side difference is affected by the placement of things like generator, water tanks, refrigerators etc. The Front/ Rear loading is obviously different and for most motorhomes the number of tires on each axle is also different. You can use the information on your placard but a better method is to get the actual tire loading and then using Load/Inflation charts establish the MINIMUM cold inflation then add 10% to get your Cold Set inflation. THIS post has some info and a link in it. Bottom Line When tires are designed, we tire engineers know that some vehicles will be driven on hot roads. Tires will normally run +20°F to +50° above ambient. You should run a TPMS to get warning of air leak due to puncture. If you are driving in the USA you should have no problems. If you are traveling to Saudi Arabia, the Sahara or Australian outback then we need to take some additional steps and precautions. I think that if you look at some of the dozens of posts on Load, Inflation and Temperature on my blog you will find more details and expamded answers to your questions.

Andy, I need to point out that the pressure in the tables is NOT to be adjusted to a theoretical "Laboratory Standard" 70°F. The Load/Inflation charts are based on inflating a tire that is at ambient temperature. This means it has not been driven on more than a few minutes and has not been parked in the Sun for more than a minute or two. In general it is suggested to check tires in the morning before travel. If you are parked so tires on one side are in full morning sun then maybe you need to plan on checking them the night before say 3 hours AFTER sundown. I have many many posts on my blog on temperature & pressure. Too many to post here so it may be easiest to add a review of those posts on your "To-Do" list.

I can't address specific issues with TST brand as I haven't used them but if you have a position that is providing a reading then it goes off then comes back on I would guess you either have a weak battery or weak signal. Did you get to discuss a signal booster with TST? Is it always the same position? Have you tried a new battery in the problem sensor? All external systems I know of go to sleep when you stop driving and there is no wheel motion for X number of minutes. They turn on again after Y number of minutes (3 to 10) of motion. Whoever makes the brand of sensor you are using they should be able to tell you the time it takes to "wake-up".your specific system. Finally RE Temperature I consider this extraneous information as far as tires are concerned. If you have a pressure loss, yes the temp will increase but the primary purpose for TPMS is to warn about PRESSURE LOSS. Some report having discovered brake drag issues or hub bearing issues with the high temp warning and thats fine, but if your tire has the correct pressure the temperature of an external sensor will be from 10 to 40°F lower than the internal temp of the tire based on my testing.so I would not worry about temperature readings as long as your pressure is OK. IF you get a high temp reading you can always pull over and see if you can touch the tire, wheel or hub. Don't burn yourself but a quick tap would tell you if you really have a hot tire or a hot hub.

Welcome to the world of "everything you thought you knew about cars no longer applies" :-) Actually there are many similarities but there are some new things you need to realize, but there is information and help available. Your tires are basically truck tires and just as you don't see tractor-trailers at your local gas station you will need to get familiar with truck stops. BUT if you check the brand tires you have you should be able to call a local tire dealer and ask if they have the space for you to pull in so you can have the tires aired up. If they are servicing the brand they sell they should be willing to help at no charge. You might check out my blog on RV tires www.RVTireSafety.com I think you will find the info you need to know on your larger tires there. If you still have questions you can always post here at FMCA.

linober You didn't specify which Michelin design tire you are replacing. I will assume it is the XRV which according to the Michelin RV tire Brochure requires a minimum "dual spacing" of 10.3". The 255/70R22.5 XZE specifies a min dual spacing of 11.6 Dual tire spacing is controlled by your wheel design so the only way to know for sure if you will be able to change the size as suggested is to get the wheel part number and confirm with the wheel mfg the design spec for dual spacing. In addition to dual spacing you need to worry about clearance to the frame, suspension and exhaust on the inside and to the body on the outside. Even if you were to buy new wheels that meet the dual spacing requirement that might create other clearance issues. Maybe you need to check other tire suppliers such as Goodyear, Bridgestone/Firestone or Toyo for replacement in your original size and Load Range if Michelin is not able to provide tires. You might also ask the tire dealer that suggested the larger tires if he was willing to be responsible for the dual spacing mis-match. Sometimes I think dealers are more interested in just making the sale than in providing the service their customers need. You might also spend a few minutes reviewing the topic of dual tires on my blog. I have 9 posts with "dual" as a label.

Hey guys. I'm still on "vacation" out West. A looong way from Akron, Ohio. In Alberta, Canada. So I don't have access to all my data files on my main computer at home. BUT Brett's reply is correct. We need to remember the primary purpose of a TPM system is to provide a warning when a tire has suffered a significant pressure loss. The Temperature readings are secondary. I have done a few posts on my blog on Temperature. THIS two part post compared IR guns with internal TPMS with a Tire Pyrometer as used in Indy Car racing to learn actual tire temperature. Note No TPM, internal or external will be measuring the actual hottest part of the tire. They can only tell you the temperature of the air contained in the tire air chamber which is always cooler than the tire rubber. Most TPMS that have temperature warning use 150 to 170F as the warning range. It is very difficult to have the internal air reach those temperatures if the tire is properly loaded and inflated and you are not running at excessive speeds. HERE is a post on temperature in general. I would NOT consider a vehicle TPM pressure reading as an accurate reference pressure gauge. Here is a post showing the real accuracy of gauges used every day by RV owners. If you review the numbers you can see the problem in assuming that an expensive gauge is a guaranty of accuracy.

Gerald if you don't know the actual load on each side of an axle I suggest you assume one side has 55%. That would mean your fronts need the inflation necessary to support. 7051# and the rears 6386# Now this is conservative but I believe reasonable as we know that few RVs load their tires equally side to side.

Cowboy, Sorry to hear of your problems. With tire wear it is always helpful if you can include pictures of the condition. "Inner edge wear" may be wear of the inside shoulder or it could be something different depending on your experiences with irregular wear. Here is a post on "River-Wear". Note the great pictures. Sorry to say I am not able to provide example pictures as I am on vacation and don't have all the info on my laptop. Some possibilities are Shoulder Step / Chamfer wear where only part of the shoulder rib is wearing. Another would be Full shoulder rib wear. or Full side wear which is when each rib is worn less than the next as you move from one side of the tire to the other. Again good pictures similar to what are shown in the post would help us provide more informed answer.

Over the past few years I have noticed that more than once, RV editorials, articles and even TV news items on tires seem to be a bit short on providing sound advice or information of educational value when it comes to tires. Sometimes attention grabing headlines are the primary objective. Two recent examples: Editorial that mentioned someone running on significantly underinflated dual tire. The owner apparently did not have a TPMS so drove 1,000 miles with low pressure. When the loss of air was discovered the tires was simply, and incorrectly, just aired up. Not surprisingly the RV owner suffered a tire failure shortely therafter. My complaint is that the author of the article who is supose to be a bit of an RV "expert" failed to mention that a TPMS would have alerted the owner of the air loss and possibly saved the tire. He also failed to mention the danger of simply re-inflating a tire that had been driven while underinflated. This is not the first time this Editor has failed to educate his readers on the topic of tire safety. TV "News" item. This was on tire age limits. While there were many so called "facts" presented that may have been the "truth" they were defiantely not the "Whole Truth". I found this article that points out some of the holes in the story. Please note the partial list of "counter points" listed. A second TV "report" was sent to me for comment. I found the item so lacking in sound logic that I contacted the reporter and offered a number of suggested actions she could take to educate herself enough to allow a follow-up "Investigative Report" but so far she had nt responded. I am thniking that in this case sensational "Film at 11" reporting is the goal and providing real safety related information is not on her radar. The point of this post is simply to remind others that many times items on a technical topic such as tires are not well researched, even when the author is supposedly knowledgeable on general RV topics, the focus of the article or news report is not providing information of sound educational value but may be simply aimed at promoting some new advertised product or just offering attention grabbing headlines like grocery store tabloids do.

Yes the opening "should" but while I have not inspected more than about a dozen different sensors, I do not recall seeing any with such a filter. Remember the goal of sensor manufacturers is low weight and low cost for the normal user and adding "shot" to the inside of tires for balance is a very low percentage occurence. If you balance your tires this way then a special valve filter is a MUST when using an external sensor. If using an internal sensor than I am not sure there is any option to avoid potential sensor damage. If there is one I would be interested in learning about it.

You are correct that an IR gun can alert you to a mechanical problem such as bearing or brake problem. An IR gun works well on heat conductive material such as metal. They do not work as well on insulating rubber which is a poor conductor of heat. If you are running low enough on pressure on one tire to get a meaningful temperature difference measurement there is a good chance you have managed to do some permanent structural damage to your tire already and simply putting air back in your tire will not "Fix It" any more than putting the Potato Salad you left out all day in the sun, will be fixed by putting it back in the refrig. If you attend my seminar on Tire Knowledge for the RV owner at Redmond you can learn more.

I am sure you would like a brand of TPM as an answer but since there are a variety of different applications and what some consider most important feature may be someone elses #3. While I do have a personal preferance, I feel it better to offer a blog post on "Best TPMS" that outlines what, in my opinion are the features for you to consider when making a purchase decision. Hope this helps.

"The internal pressure sensors are the only ones that are immune." Interesting. The internal sensors I have seen from a number of different manufacturers have small holes where the pressure sensor is located. I could see this hole easily getting blocked. But I have no data to go on, so cannot pronounce this good or not. Just a concern till I learn otherwise. Wonder if the "shot" manufacturer is willing to warranty that their product will not harm an internal sensor.

Thanks for replies. I have received some feedback on other site so will be changing the system. 1. Increasing the Inverter to a 750W unit by Husky 2. Am moving the Inverter and relay out of the Battery box to area under counter. I will monitor the temperature of this area to see if I need for the inverter fan to blow through opening in counter face into living quarters or if the air space under counter which runs around the water tank is large enough. 3. Will be connecting the inverter positive side using 10Ga wire 2' long directly off the Coach Battery relay that is already under the counter. This line will have 50A fuse in it and a 50A rated "trigger" relay. The Coach Battery relay is connected to the Deep Cycle coach battery w/2G wire provided by coach mfg.. 4. Will run 6' of 6Ga directly from Battery ground to the Inverter. 5. The trigger relay will still be activated by combination of Ignition Hot plus a rocker switch. Will lower fuse on the trigger line to 2A 6. The 120V Inverter output will use 14G to the DPDT switch and 14G from DPDT to the refrig. The total length of the 14G from inverter to refrig through the DPDT switch is 12' Not sure what to do about the battery disconnect switch, which is not part of this refrigerator / inverter system but just a disconnect on the ground side of the coach battery. Many of these switches are sold for various applications in car, truck, boat and RV application. Some concern was expressed about battery explosion with my components in the battery box but none of these would in my opinion be "sparking" under normal operation. The batter disconnect switch almost always emits a small "zap" whenever I connect the battery to the system. This to me would make this a more likely cause of battery explosion than having the inverter and relay in the battery box. This obviously is a separate question for those knowledgable in 12v system and battery safety. Thanks again for the replies.

After listening to Mac "The Fire Guy" at a couple of FMCA events I no longer run with the propane valve on when driving. In the past most trips were relatively short so the temp of the fridge has not risen too much but since I am headed to Redmond, Oregon from Akron, Ohio I have a number of long days ahead of me so I decided to Mod the electrics. Biggest problem is that the Coachmen wiring diagram is more of an estimate on what the staff did when they assembled my Freelander. No color coding, no wire sizing identified and numerous un-used wires and connectors along with some uninsulated wires just laying under the floor. Sooo after doing a lot of testing and creating my own wire diagram here is what I did. Refrig needs 2.7A @120V or 324Watts. Harbor Freight has a nice inverter rated at 400W continuous I have space in my battery box to permanently mount the inverter. There is an Ignition hot feed in the battery box area. Ran wire from Ign Hot to a rocker switch in the control panel by the door. Then from this switch to a relay in the battery box. The relay controls the power from the battery to the Inverter. Eliminated the battery clamp connections off the inverter and using ring or spade terminals w/heat shrink tube on each end, made all the wiring permanent. Battery to Inverter is 10Ga 120V Inverter to DPDT switch is 14Ga HD exterior rated extension cord. 10A fuse on the Ignition hot connection to the rocker switch 120V output from the inverter runs to a DPDT switch. This switch connects either the Inverter or shore power to the Refrig so isolates the two power sources. Still to-do is label the switches Now when driving down the road my engine alternator is providing ample power for the Refrig and if I shut off the engine there is no drain on the coach battery. The rocker switch and the DPDT switch are redundant in controlling when the refrig is running off the coach 12v system.

RE balancing with "shot". Yes this appears to work for many people. You need to remember that by adding material to the inside of the tire you may have voided the warranty. You need to consult the tire MFG and read the fine print in the warranty. The other concern is the potential for dust from the "shot" plugging the sensor in a TPMS which could render the sensor scrap. I believe there are special valves with filters on the air chamber side that can prevent the damage to TPM sensors. Note i said "potential" as I have no information on the specific material or warranty from the "shot" MFG that their product will not damage a TPM sensor.

I have a post on my blog with pictures of the wear on front tires with a Camber problem. Also covered what I did with rotation AFTER I had the alignment set to the proper specs. I will be at Redmond and have two seminars on tires. Stop in and say "Hi"

If the leak was a loose bolt in valve i am wondering if the valve or at least the rubber gasket around the valve was replaced when you got the new tires. The rubber part of valve system can "age out" just like a tire can. Whenever you replace a tire it's good insurance to replace the valve stem rubber parts at the same time. There are torque specs the tire shops should use but I think most just tighten till it "feels" good.

You are correct. I think it is possible the original information may have been misinterpreted. To my knowledge most "Metal" valve stems are made of Brass. Some are plain Brass color and others are Chrome or Nickel plated. Most bolt-in TPM sensors are Aluminum and as posted above a small dab of never-seize or Di-electric grease is needed to lessen the chance of corrosion. Since you will probably be needing to add air every month or so you can keep an eye out for corrosion. I have been running external sensors, with Brass threads on Aluminum TPM stems (yea I run two TPM systems as part of a long term test). I do remove the external sensors when no camping is scheduled for a few weeks and I make sure the threads are lubed when I re-apply the sensors. You don't need a lot just enough to coat the threads. I would recommend against using anything like RTV or Silicone as you don't need a pressure seal and a small piece of cured Silicone could get in the valve core and cause a slow leak.

James, If the a tire is properly inflates the temperature will probably be between +30 and +60F above ambient depending on speed, load and aerodynamics. I can tell you from personal experience that the hand held IR temp guns that many have, can not locate and properly measure the localized hot spots in the base of the shoulder slots. Rubber is not like metal where the temperature will be relatively uniform. Tires have very localized hot spots as seen in THIS post. If you are going to make any effort to monitor anything it should be the pressure and TPM will do a much better job than occasional check during driving breaks.

The information on THIS post includes examples of DOT serials. Tire treatments will not extend tire life past the manufacturer's recommendation, and I know of no tire company suggesting more than 10 years in RV application. The best protection for tires is the use of white tire covers.

As with almost everything technical about tires there is no simple answer. Not all "rubber valves" are the same. and not all TPM sensors have aluminum stems. The problem is how to know what you have. Basic "rubber stems" such as TR413 as seen at this web page (Note the price) are rated for 60 psi max. There are short and long versions of this stem that except for short brass threads at the end are all rubber. I would NEVER use an external sensor on this type of stem and expecially not on the longer TR 418 Many OE TPMS have aluminum stems and an aluminum nut on the outside and may look like this Some newer OE TPM sensors have what looks like a standard TR413 but actually have a brass core like this. You can read about bolt in high pressure stems HERE. Now I personally have aluminum stem internal sensors. I also use external sensors when doing comparison testing of different TPM systems. I would also use external sensors if I had the OE brass stem sensor or just a standard metal bolt in stem. Without some more information it is impossible to know what you have on your vehicle. Sometimes just looking at external aluminum is enough sometimes more investigation is needed. IMPORTANT INFO. You cannot simply look, see rubber and assume that you have a TR413 type stem. The fact that you have not failed a stem does not mean you provide testimony that it is OK to use external sensor on any stem that appears to be rubber. Based on this thread I will try and write a full post or article on this topic soon.

Not sure if I would be concerned with different size front & rear. I agree with Brett in post #2. RE ABS I would contact Newmar and confirm if the unit has ABS. If it has ABS, is there a computer connection between the Front & Rear tires/brakes? RE rear end dragging. The radius difference is only 0.8". If you know the wheelbase and the distance from the rear axle to the rear bumper we can calculate the increase in clearance to the road at the rear.