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Thursday, July 31, 2014

Are my tires too old?


 How old is too old ?  The guy may have a lot of "life experience" and be older than the normal rider, but can you say with certainty he is too old to be riding a bike?

After reading my posts on the benefit of using white tire covers, a reader noted my comment on having tires that were 7 years old on my coach. He thought I was not practicing good preventive maintenance as he had heard that all RV tires should be replaced by 6 years "no matter what".

I offered that the recommendation on the max age of a tire on an RV is not as clear cut as some would believe.

According to this RV tire guide from Michelin they recommend annual tire inspection by a qualified tire dealer after 5 years but replace at 10.

I have seen posts such as this on RV forums " The Michelin RV Tire Guide specifically says  that  tires may be good for  up to 10 years, but  recommends that they should be thoroughly inspected annually, especially after five years.  This same information is summarized in the Michelin TSB on Service Life for RV Tires:
The Michelin Truck & RV Tire Warranty is for the life of the original tread, not a fixed number of years, and starts on the purchase date .Sidewall date is used only if you have no sales invoice.
Note, however, that passenger and light truck tires may have different parameters. If your motorhome uses 16" tires, I would apply the passenger & light truck recommendations.
That said, I will continue to replace my tires at the seven year mark. Far too much risk of a blow out beyond that point.  The risk of body damage or accident is just too great for me
."

Now I have not been able to confirm every statement about tire life that people post on different forums. The above examples are from Michelin and are about tires on cars, trucks and motorhomes. There are those that say for RV trailer application 3 to 5 years is a maximum.

Here is a good editorial from a trade publication on the topic

Clearly there is no simple answer. As a tire engineer I can tell you that there are just too many variables that would need to be considered before a simple xx months max type answer can be provided.

Some variables would include time spent exposed to direct sunlight, time spent at temperatures above 80F, 100F,  120F, 140F or above. How much reserve load capacity (Load capability minus actual load)  for each tire. Amount of time spent at or below the minimum inflation needed to carry the actual tire load.

My tires have been in service since April 2008. I run 15 psi above what is needed for the actual individual tire load and the tires have never been lower than 8psi above the minimum inflation needed. The tires are always covered if I am parked for more than a day. I have not traveled where the temperature exceeded ever exceeded 90F. By training and experience I am a Forensic Tire Inspection Specialist so am fully qualified to do internal and external tire inspections.

I will be replacing my two front tires next Spring and two additional tires each year there after.  BUT this does not mean you should not be replacing your tires when they are less than 10 or 8 or even 5 years as the "life experience" of your tires is different.

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WATCH A VIDEO: How your RV tires can "age out" before they wear out.

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Monday, July 21, 2014

TPMS Batteries

Many have smartly made the move to add a Tire Pressure Monitor System to their RV. While TPMS will not eliminate 100% of the possibilities of having tire failure they can eliminate many "Blowouts" as they can provide warning of air loss. Many times giving the driver an opportunity to pull over in a safe location and to avoid destroying an otherwise potentially repairable tire.

One issue with TPMS is battery replacement and battery life. As we all know from personal experience it is almost impossible to accurately predict when a battery will "die". While we might not be able to predict the "when", there are steps that can be taken with external sensors to extend the life of the batteries and possibly prevent having a battery fail and leak and damage the sensor.

When I was shopping for an External Sensor TPMS to buy,  I selected TireTraker. I used the selection criteria I outlined in THIS post.




 The user replaceable
 low cost batteries were a major consideration.

Now I am not a full timer so my RV is parked for weeks at a time and for months over the Winter here in Ohio. Now while the "Standby" mode of the sensor only draws 500nA so the "life" is not draining out very fast but there is still the potential for the battery to fail and corrosive chemicals to leak out and damaging the sensor. Remember your battery drain rate may be different.

Here is a suggestion.

Get one of those pill boxes and place a battery from your sensor in each section. I have six sensors so I have space for a new sensor battery as a back-up to the others.

Next label each sensor with the position it is associated with. This will eliminate the need to re-calibrate the sensors when you place them back on your RV.



This storage approach prevents the metal batteries from shorting out against each other too.


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Tuesday, July 15, 2014

Can I change from ST to LT tires on my Trailer or 5ver? Part Two

In Part 1 we left off with having to do some calculation.

I will assume you have confirmed the actual individual tire loading and have moved some heavy items around to end up with a reasonable balance of loads,

I will also assume you still want to change from ST type to LT type tires which means you must increase the Load Range and or increase the tire size to get a load capacity in the LT to match or exceed the capacity of the OE ST type tires.

Now before we move on you need to realize that "LT" is a designation used here in the US and European and some Asian countries have what they call "Commercial" tires. These Commercial sizes do not start with LT or CO but will probably look like 7.00R15  or for metric sizes 205/75R16The "C" in this case is not the Load Range but stands for "Commercial". The Load Range will be identified as normal LR-C, LR-D etc or possibly with RL or XL for Reinforced or Extra Load. To make this post easier to read I will limit my comments to LT type tires. Just remember there are other options that may be better for those with 15" or 14" wheels that do not want to change rims.

NOTE: All of these letters and numbers are important when selecting a size so be sure you record them all when doing your research.

So on to step
#6 Dimensions. There are two key dimensions Outside Diameter or OD and Width. Now I am confident that we all understand OD but width can be a bit confusing. Depending on the wheel well contour the overall maximum width or "Section Width may be most important. Some tires may have a narrower clearance nearer the tread so they will need to do some actual measurements at a number of locations.
It may be easiest to use the dimensions for OD and Section published for your current tires and just do a confirmation with your tape measure. Remember tire "width" is not the same as tread width.

You need to be sure the tires NEVER contact any portion of the RV frame wheel well or bodywork. You should try to have equal or greater clearance with the new tires that you have on your original size.

7. The challenge
When moving from ST type to LT type you will need to move up in Load Range or up in Size or both.

Now comes the research to see what your options are
8. Knowing the target Load Capacity and the maximum OD and Section width, it's time to use the Internet to do some research. The objective is to find tires that meet your needs for the numbers and that are appropriate tread pattern. You certainly don't need Snow Tires or heavy traction tread pattern. I would suggest that the tread be identified for "All Position" or Steer for your trailer application.
You can go to web sites from large dealers such as Tire Rack, Pep Boys, WalMart, NTB, Discount Tire or similar. You might also just Google "Trailer Tire" + the name of a large city or town near your location.
Once on their web site find the various possible tires that meet your needs.

9. If you are increasing the Load Range with the associated increase in inflation you need to confirm the wheel can manage that higher inflation. The info may be marked on the back side of the wheel or you may need to contact the wheel seller or manufacturer or you may need to get different wheels if your OE seller doesn't know what the rating is for the OE wheels

10 Finally, as I have previously suggested in my post on "The Best Trailer Tire" you need to make your purchase decision not just on lowest price but need to consider the tire warranty, even if there is a Road Hazard Warranty. Also how easy will it be to get a replacement if your tire gets a sidewall cut or unrepairable puncture.

11. Last step:  After all this work we want to do a first class job. Some might want to say you can't change from ST type to LT type due to Federal Regulations. Well a friend Dave Gray has an excellent post just on this topic. He has even provided an example of what would be the appropriate label you should apply after making modifications to your RV.


I hope these two posts have helped you understand the steps, calculations, measurements and research needed to make such a change.



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Tuesday, July 8, 2014

What is "Cold" Inflation? Quick Post

The definition from US Tire & Rim Association is
Cold Inflation Pressure is the inflation pressure taken with tires at the prevailing atmospheric temperatures and do not include any inflation build-up due to vehicle operation

 In real life this means before the tire has been driven one mile. It also implies that the tire has not been exposed to external warming from being in Sunlight.

We have shown that when a tire is in sunlight for as little as 30 minutes the temperature can rise by almost 40°F which will give you a higher than Ambient pressure reading.

You should wait at least 2 hours with 3 preferred after end of the day driving with the tires in full shade, to give them a chance to equalize temperature with ambient air temperature.

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Monday, July 7, 2014

Is it OK to Replace Bias tires with radials

My 25' 1985 trailer has a plate on the left front street side that indicates 7.00 X 15 and 45 psi. D range, I think.
Right now, there are Roadkings LT on it. I inherited the Airstreem from my aerospace engineer Dad and know based on 5+ years it's time to replace them So, what manufacture would you recommend and what pressure? GVWR is 6,800#, axles are 3,200lbs. I believe the original tires were bias.
It really isn't difficult to find a new radial tire for your RV but there are a few basic steps needed.

You gave the GVWR and Axle rating but made no mention of the actual load on each tire. There are a number of posts showing that the load is seldom split evenly between axles or evenly side to side.
There are worksheets available to help you calculate the individual loads if you can't find a location with individual scales (this is difficult to do so use the worksheet). Here are 2 sites with forms you can use.
Bridgestone Commercial Truck Tires
RV Trailer Weight Calculators - Towing Capacity - Ratings


OK Lets assume you get or calculate the individual tire loads. For this example I will use the following numbers 
LF 1,550      RF 1,390
LR 1,500      RR 1,440

I would recommend a 15% "Safety Factor" or "Reserve Load" when looking at the tire loading.
1,550 + 15% = 1,782#

I also recommend an additional "Safety Factor" of +10% on the air pressure
You need to find a tire capable of carrying at least 1,782# at its Max pressure -10psi

The +15% is a safety factor for possibly different loading in the future
and -10 psi is to allow you to set a pressure and not need to worry about changes in ambient day to day.

Now since we are talking a multi axle trailer you need to run the max pressure in the tire all the time. This has been covered in other posts in this tire blog but it has to do with the unique side loading for trailers.

Consult the tire Load/Inflation tables and tire specification sheets to find a tire that meets the above load & inflation capability and fits your trailer for width and OD.

One final consideration. Years ago when there were still many bias tires in the market the wheels were not always designed for radial tire loading. You should probably also either confirm your wheels are approved for radial tires or also get some new wheels.


It's not hard to do this but you do need to spend a little time doing the research correctly.

PM me if you need help

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