tireman9

I have read a few posts both here at FMCA as well as on other RV forum sites when the topic of what to do when a tire fails and you don't have a spare. Many times it has been suggested that the person plans on "limping" home or to the tire service center with just one tire in the dual position of their RV. While on the surface this might seem to be a reasonable approach, there are a few things that need to be considered. First, unless you have a TPMS that warned you that one of your duals was loosing air, in all probability you have no idea how long you drove with one dual underinflated. If you don't know when the tire started to loose you also have no idea at what speed you drove on one underinflated tire and also on one overloaded tire. If a tire looses more than 20% of its air it is considered to be "Run- Flat" by tire industry If you have driven on a "flat" tire it is considered to have been damaged and should not be considered for future safe usage. What is not obvious when you read the above is that is one tire of a dual goes flat the mate has now been overloaded. I covered some of the info in a post on the Special Considerations for Duals, but there is more that needs to be considered. If you have one tire punctured and loosing air the mate is "taking up" the load for both tires until it is 100% overloaded. Driving at highway speed will do serious internal structural damage. Most of which cannot be seen with out special equipment like X-Ray so it is simply considered scrap so now you need to replace two tires. Trying to "limp" means that you need to reduce your speed and according to the special tables in Tire & Rim Association for adjustments for speed, inflation and load your limp speed is not 30mph or 20 mph or even 10 mph but it is limited to 2 mph. That is TWO miles per hour Maximum. Any more and you are damaging your tire beyond repair. The solution would be to call for service. I would only drive on a single tire for a hundred yards at most to get to a location where I could safely pull off the roadway.

I posted some information on how to get reasonably dry air for your tires if the change in pressure is of concern to you. http://www.rvtiresafety.com/2012/05/how-to-get-dry-air-for-your-tires.html To help everyone here is what really happens to the "air" in your tires. The Nitrogen is less reactive than the Oxygen so the Oxygen tends to migrate through the rubber at a faster rate than the other gasses. In general all tires will loose from 1% to 3% pressure each month when all the variables are controlled in the laboratory. Temperature change has the biggest effect on pressure but Elivation and Barometric pressure also have an effect. We have run experiments where we measure the %N2 in a tire and over a period of a year as the O2 "leaks" out and more air is added to maintain the tire inflation level the net effect is to increase the % N2 in the tire air chamber by a couple %. This is measurable but not really meaningful in the big picture. By the time you increased the N2 % to say 82 or 84% the tires would probably be be worn out or over age.

Nancy Bretts coments are correct. To you and others concerned about needing a compressor on the road I am not really sure it it is necessary or the best way to allocate your money. If you are going to spend a few hundred you would be much better off investing in a TPMS that will give you low pressure warning even while driving. While setting the correct pressure is a "Hot Topic", if you have done the basics of getting the actual corner tire loads and confirmed the minimum cold inflation then add 10% cushion. All tires will loose are but only at about 1 or 2% per month so unless you have a leak or puncture you should be good for at least a couple of months or more between needing any air at all. Pressure will change with temperature http://www.rvtiresafety.com/2012/04/how-do-i-know-what-my-hot-pressure-and.html Only a little bit with elevation so you should not need to be adding air till you have lost at least 5% of your cushion. If you discover you have lost 10 to 20% of your air over a day or so since you last checked your pressure, you have a more serious problem and the problem needs to be fixed. If you are loosing air that fast a compressor will only give you enough air for a short drive and driving on a puncture or damaged tire could lead to more damage or even a blow-out. Bottom Line Once you properly inflate your tires you should be able to get them aired up for free every few months and never need a compressor.

If you look at the statements from the tire mfg they basically do not want "stuff" that can harm the tire to move to the tire and hurt it. Oil from asphalt or water from dirt/sand. It isn't the grass but the moisture that can migrate into the tire over time from the dirt or sand. I would think that pavers would be reasonable. Personally I have some 2x10 that are large enough to support the complete footprint that I place over the gravel where I park for the winter. Inflating the tires to their max is a good idea. If you can remove some of the load that would decrease the rubber "set" that can occur too. Don't forget the white tire covers to protect against excess heat and UV and no electric motors or devices like ozone generators near the tires or in the same garage if indoors.

Not sure why HF changed the link but here is the P/N if you need less than 90 psi: item#68215 1/4" pipe threads are standard on most air chucks. Also I keep mine in a ziplock bag so the desiccant is good all Summer. There are similar products available at many auto parts stores. just ask for air dryer for air tools. Note the HF "filter" P/N 68224 is not a desiccant as it filters out moisture that has condensed in your compressor or air lines. You have given me a good topic for a blog post. Give me a week or so to do the research.

I think I covered most if not all the questions in my blog on Nitrogen. Bretts comments on dry are are very appropriate.

Was the dealer a company store or independent dealer? If company store you might be able to get some assistance from BFG on getting the tires changed to the H load range you need to carry your load. The Utah dealer should know better. RE Mixing brands: In a pinch I might do it on the front but would really prefer to have all tires on an axle the same brand, size, and load range. For duals you have a couple of things to consider. 1. Their history... See this post. 2. Their circumference. While inflated but not loaded you need to ensure that both tires in a dual position are within 3/4" measured circumference.

Hi Phil, First off be happy your RV manufacturer provided you with tires that can easily carry your loaded weights. Too many owners discover they have been sold a unit with tires that are almost in overload as soon as they leave the dealership and fill the tank with gas/diesel. Now to your specific question. I agree with the info provided by both Andy and Brett. While my thought process is slightly different we end at essentially the same end point. Start out no lower than the lowest inflation on the Michelin chart. The only exception to this would be if you get something IN WRITING from Michelin corporate (NOT THE LOCAL DEALER). Since you don’t have actual individual tire loads of the fully loaded RV I suggest the following: Assume a side to side variation of at least 5% so you calculate a 55/45 split. Using the 55% of total load I check the company tables to find the minimum inflation needed to carry that load. NOTE you are going up in the inflation in the table to the PSI that exceeds your calculated load. For those pulling a multi axle trailer you also need to assume a 55/45 axle to axle load split before you do the 55/45 side to side split. I then add at least 5% to the table inflation and again round up to the next 5 psi to allow for daily temperature variations and to have an easy to remember inflation number. This extra 5% means you are not chasing your tail and trying to calculate and adjust the pressure every day. Remember all tires will loose 1% to 2% air each month in addition to the variation due to temperature, elevation and minor variations due to barometric pressure. So unless you enjoy spending a half hour every day calculating and adjusting your pressure just add the extra 5% so you only have to add air every couple of months or so. FYI If you are going to FMCA Int’l Family Reunion in Indianapolis check the schedule as we are reviewing the schedule and I think I will be presenting my Tire Basics for the RV Owner on Tuesday. If you make it be sure to say Hi.

Brad Where did you find the data indicating "extra side-wall". I see thicker rubber to protect against you running against curbs but this will also increase heat generation, I find in the 255/80R22.5 XZE* LR-H 5510# @ 120 psi and 18/32 tread depth XRV LR-G 5205# @ 110 psi 16/32 tread XZE LR-G 5205# @ 110 psi 20/32 Not quite Apples to Apples with three different read depths and two different Load Range. I think if you read the sidewall you will see the actual constructions to be one ply of steel in all three tires. Note the extra tread depth will probably lower fuel mileage. When I read the Features and benefits info I would think you want longer sidewall life (ozone resistance) rather than heavier tread depth, unless of course you wear out your tires before they age out.

Harry Brett is correct. There are a lot of BUBBAS out there. If someone ever sold a tire or got paid to change a tire I guess they are entitled to call themselves "professional" but I would certainly not consider them "competent" to perform a meaningful tire inspection. Having taught hundreds of tire "professionals" and engineers in North, Central and South America I can attest that few have spent the time needed to learn much of the art involved with tire inspection. Finding a person competent to do "end of life" inspection is just as hard as finding a competent heart or brain surgeon. Just knowing how to handle a scalpel does not make you competent in all forms of surgery. But none of this helps you. So to your question. First off sidewall cracks are seldom, in themselves, the root cause of a tire failure. Just as high blood pressure is not the “cause” of a heart attack. BUT just a high blood pressure can be a symptom that suggests hidden issues that might lead to a heart attack, the sidewall cracks are an external sign of the higher probability of internal structural issues that could be of concern. There are two areas of concern in the tire structure and they are close to each other. At the edge of the belts in radial tires, where the most heat is generated the heat does cumulative, irreparable weakening of the rubber in that area. This loss of strength can ultimately lead to microscopic cracks which will grow with time and use. If the cracks get large enough the surrounding rubber can tear and then you may get a detachment of the tread from the belts or between the belt edges. Here is a picture from the NHTSA publication. This tire has not come apart yet but will do so if the owner had continued to drive on this tire. The Pneumatic tire pg 627 This is a very technical 700+ pg document. Will give most non-tire engineers a headach, but I do need to provide the source for this picture. Now there are inspection procedures using X-Ray and Holographic inspection machines but the cost of doing such an inspection would probably exceed your cost of a new tire so many time it is simply less expensive form of “insurance” to replace the old tire when the external warning signs such as cracks exceeding the size established by the manufacturer or the tire has reached the manufacturer’s recommended maximum useful life. Sometimes it is possible for a very experienced tire inspector to see signs of impending failure on the exterior or interior surface of the tire but while the presents of such indicators may suggest a high probability of impending failure, the lack of these signs is no guarantee there are no internal structural issues. Following the “better safe than sorry” philosophy means that once the tire has reached the recommended age limit and or is showing excessive levels of external cracking it is time to replace the tires. I would consider the replacement just like insurance. You don’t plan on having an accident but driving without insurance is a risk few are willing to take. If you are not sure who to trust, then I suggest you find a tire store owned and run by the tire manufacturer and not just “Bubbas bait and tire discount store” for it is more likely that someone working for the manufacturer will have received at least a little training on in the art of tire inspection. You can always get a couple of opinions too if that will make you feel better but at 8 years the clock is ticking pretty loud. If your tires still look good the dealer might even find a buyer that tears up his tires in dump truck or trash hauler service.

Spec is 1/4" but in real life few have the tools to accurately measure the Diameter. Once the tires are off the ground you can more easily measure the circumference and check that they are within 1/4". Note dimensions published are new tire and all tires grow a bit but all at different rates so you really can't compare published dimensions. Especially across two companies. More info of the special considerations for duals HERE.

I agree with Brett, but would like to expand on the topic a bit. I think it best to think of a tire "Max speed" a bit like the engine red line. Can you exceed the red line on your engine? Yes, occasionall,y but is it good for the long term durability of your engine to run at the red line? I think you will agree that that is not a good policy. A tire has a finite life and heat and cycles consume that life. Heat comes from under inflation, overloading and fast speed along with spending all your time in the South. Heat generation occurs inside the tire structure at the molecular level. It is not linear so 1 mile at 75 “uses up” more of that limited life than 2 miles at 40. It’s even possible that a mile at 80 is worse than two at 60. The max speed rating is also based on the assumption that the tire has NEVER been operated while “flat”. Note that a loss of 20% of the minimum inflation needed to carry the load is considered “flat”. Also if the tire has ever been repaired the manufacturer may no longer support the speed rating marked on the tire. You need to consult the manufacturers publications to confirm their policy. This would apply to tires with a Speed Symbol letter as found on most Class-B & Class-C motorhomes and a few Class-A units. An example might be LT235/85R16 LR-E 116/120Q The 120/116R is the Service Description with the 116 and 120 being the Load Index and the “R” being the Speed Symbol for 99 mph. Class A might have 255/70R22.5 LR-G 138/134L the “L” is the Speed Symbol for 75 mph. I know of no highway tire that can run its entire life of 40 to 90,000 miles at its max speed. The tests to establish the Speed rating only require an hour or so to complete and most of the test time is well below the max. Finally. If you tow a trailer or dolly that has ST type tires you need to remember they are rated at 65 MPH max and a few trailers come with commercial tires that are only rated to 62 MPH so your max speed is based on the lowest rating of any single tire.

I understand the alternate interpretation of "Gross weight" as possibly applying to the load on each tire but that doesn't make sense either, as the full statement from RVDA is "Independent braking system is required in each weight bearing wheel where gross weight exceeds 1,300 kg (2,867 Ibs). Breakaway brakes are required on all trailers 1,360 kg (3,000 Ibs) and over." If we are talking individual tires then heavy trucks would need as many as four "independent braking systems" which I am confident is not the case. I have never heard the term "gross weight" being applied to individual wheel positions. I tried asking Société de l'assurance automobile du Québec for a clarification but they just directed me to a page with most or all traffic laws in French. What I believe we have is a failure to get an clear and accurate translation. Too bad I can't find this within FMCA. I have learned that a number of provinces would seem to require electric brakes that "can be applied by the driver" which would seen to preclude surge brakes. http://drivinglaws.a...trailer-brakes/

Found this Quebec requirements say "Independent braking system is required in each weight bearing wheel where gross weight exceeds 1,300 kg (2,867 Ibs)." This would mean I need three "Independent" brake systems. One for the RV, One for the Dolly plus one for the reat tires on the car. http://www.rvda.ca/ProvBrakeReqts.asp Looks like Tow Dollies are not an option in Quebec.

Hadn't heard about the "all axle have brakes" requirement. Can anyone shed some light? This sounds like a wonderful one page info sheet for FMCA to publish. While we are not planning on All states we do plan on Canada in next few years. If I don't do Dolly I have to buy a new car or not tow.

Thanks for all the answers. I have decided on electric brakes so that eliminates some units. Am leaning toward STEHL as there is a dealer 10 miles from home and they want $1395. Having a dealer close by means I should not have any warranty issues. Next up will be the in cab brake control. Am looking at Reese Pod or Brakeman. Also some kind of splash guard to across back of the motorhome. Any thoughts on the one that are a brush like material. Do they work as well as the solid rubber sheer?

The used dollies went fast so right now it looks like new. I have a local dealer of STEHL offering a dolly w/electric brakes 14" tires and tie down straps for $1399. Dealing with local dealer would make any warranty issues easier to resolve. Any comments or concerns with STEHL? One thing I would do right away is to confirm tire alignment and check bearing lube and electric connections.

Have found 3 used Master Tow dolly locally at $750 - $1000. None have brakes which I definitely want. I see that I can buy backing plates, Hubs and a wire harness from Master Tow for $300. If the plate & hub are standard trailer parts, which I would think they are, I might be able to cut the cost. Is this just a bolt on swap? I am very handy with tools, just haven't been able to look at the Master Tow units closely yet.

Can you get a clear picture of the condition? You might look at these examples. Uneven can be just about anything

Interesting reading. We have a small Class-C and get 10.5 mpg on gas. We do not full time. My car is a 2010 Hyundai Elantra auto so it is not good for 4 down and I only have 15k on it so selling really isn't an option. I have no space problems at home so storage of the dolly is no issue. In the past I raced a Camaro and had a 26' enclosed trailer so tying down a car to a dolly should be a non-issue for me. I think a dolly is the right choice for my situation. - Questions: Surge brakes or electric on the dolly. My experience is with electric and I like being able to apply trailer brakes manually in certain situations. I am guessing a 1 or 2 mpg hit on overall fuel economy. Does this sound reasonable? I note the brands mentioned - Tow Master, Roadmaster and Acme and have heard of Remco will Google them to see what my options are. Other brands you might recommend? Thanks in advance for your comments and ideas.

Bill. Sorry to say there is no good way to predict the ride difference, if any when you are not changing inflation pressure. I did significant NVH (Noise Vibration Handling) vehicle evaluations and you would be surprised at how different vehicles respond to similar tire changes. Never did a Class-A NVH test though. If Mich lists both Regional and Long Haul on their RV tire page. I would select one from that page if you have decided to go with that brand. If all else was equal you will probably get better fuel economy with shallower tread if that makes a difference. Good Luck and let us know what you learn after you get the new tires.

OK got the info and I understand it. Now lets see if I can translate Tire Geek speak to English. 1. The load and inflation information on the Michelin web pages for the 275/80R22.5 LR-G and LR-H are correct. 2. The rated load for these two tires is different, even at the same inflation. 3. The reason is that the LR-G was designed to US Tire & Rim Association "TRA" standards and the LR-H was designed to similar but not identical European Tyre and Rim Technical Organization "ETRTO". 4. TRA calculations and tables were calculated in "inch" units while the ETRTO and other similar organizations like The Japan Automobile Tyre manufacturers Association "JATMA" have always been metric based. Now introduce the fact that you take a tire originally intended for the European market and try to match it to the tire developed for the US market and convert the units then do the rounding such as the 123 psi for the max of the European LR-H etc etc and you end up with confused customers. So bottom line. Use the information for dimensions, load, and inflation for a specific tire as published by the manufactuer of the tire you are considering. You can still consult other sources but you need to remember that there may be slight variations. Just FYI here are just some of the source books that tire engineers need to consult and follow during the design process.

While I can't offer advice on where to get the work done I would suggest you call first as many tire stores and alignment shops are not equipped to handle what is essentially a heavy truck front end alignment. You mentioned Firestone tire store. Many can not handle heavy trucks but you might check their web site for store locations near the RV location. That link also has an "Ask the tire Doctor" link and I found this reply concerning right front tire shoulder wear after front end parts change. " If examination of the left-front tire shows no side force wear then a likely culprit would be a positive camber angle on the right-front. a. Was the steering axle replaced as part of the repair? b. Did the alignment shop give you a print out of the alignment specs, as received readings, and after- alignment readings? c. If you do have such a print out, make sure the right-front CAMBER angle is either 0 or slightly negative. Any positive setting will lean the top of the tire out and wear the outer shoulder on the tire. d. If the right-front does have a positive camber angle, the axle should be replaced (do not bend the axle as this voids any warranty)." There is also a post on a similar type of shoulder wear "From the description of the irregular wear that you give, its sounds like you are describing what the Technology & Maintenance Council defines as Cupping/Scallop (Shoulder Wavy) Wear. TMC describes the appearance as: "Localized cupped-out areas of fast wear creating a scalloped appearance around tire on the shoulder ribs. May progress to adjoining ribs." TMC gives the 'Probable Cause" as: "Usually a result of moderate to severe assembly out of balance condition, improper rim/wheel mounting or other assembly non-uniformity. Can also be due to lack of shock absorber control on some suspension types as well as loose kingpins and improper bearing adjustment. Underinflation can also cause this condition." Here is a link with pictures and probable causes of various types of irregular wear on tires.

BillO First off try to separate out the Axle Load info and calculate the individual tire load. I have no Idea why Michelin is different. Sometimes I think they do things different just to be different. Second. Take a look at the actual tire designs you are considering. Michelin lists different designs with different tread patterns and tread depths. Remembering that in general thicker rubber runs hotter than thin. Hotter is more likely to fail than cooler. These design features come into play when passing a given test. Now it might be possible to make a table with many features and dimensions of the difference between the different Mi designs but that's a lot of work and you still might be overlooking some special construction feature. The other item is you are really looking at 10 psi difference to gain 90# load capacity per tire. I would agree that 10 is significant as this is 10% but do not think 90# is significant as it is closer to 2%. I am inclined to believe that Michelin gave the higher load rating for some marketing reason to meet some truck manufacturer specific need for the extra 180# on an axle. Now I am also not sure if you could actually feel a 10 psi difference in a blind over the road evaluation and even if you can it would not be something that couldn't be achieved with a bit of extra cushion on the driver seat. A quick review of a tire that might be good for RV application is the MI XZA3. This design has a G & H with the G rated at 6175# @ 110 and the H at 7160 @ 120 psi. I cannot explain the difference in the numbers. Possible error in the Michelin web page?

Lets see if i can shed some light to help clear up the confusion. Since the load is carried by the air and not the tire it is reasonable for tires to have the same load capacity at the same inflation, no matter the Load Range. You can read more at this site. I took a look at the Load/Inflation tables at Firestone pg 4 of 9 and find the LR-G tires are rated for 6175 Lbs @ 110 psi and LR-H 6610 Lbs @ 120 psi. Goodyear page 15 we see the ratings 6175 @ 110 and 6610 @ 120 for the G and H Load Range. Michelin tables for size 275/80R22.5 LR-G shows 6175 at 110 psi but LR-H shows 7160 Lbs @ 120 psi. NOTE the different Load Range Michelin tires are also of different design so there are a number of possible reasons the 7160 Lbs is different for the other tires. This shows why it is important to check the Load/Inflation tables published by the manufacturer of your specific tires. Industry Standards as published by Tire & Rim Association show a 295/75R22.5 and 275/70R22.5 as being rated the same at 6175 at 110 for LR-G and 6610 at 120 for LR-H. If a manufacturer makes some special provisions or design changes and tests to a different load they may choose to publish load capacity that is slightly different than you might find for a different design or from a different manufacturer. To answer your final question, you can not simply change the Load Range but not change the inflation pressure and assume that you will have a different load capacity. You must use the tables from your tire manufacturer for your exact tire and be sure you always check your inflation and have enough air to carry the load. You did not say what your actual loads are I can't look at the possibility of there being a choice of a tire that would allow a lower inflation but I doubt the inflation difference would be very significant.