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Friday, August 16, 2019

Is it true a pick-up tire is better than a trailer tire?

That's a question I received the other day. Here is my reply.


Well, I'm not sure, is Spaghetti better than Lasagna?

Ok seriously. No good way to answer your question as an LT tire is intended for passenger-carrying vehicles while ST type tires are specifically designed for trailers not carrying any passengers.

The Load formula for these two different type tires is different, just as the formula for P-type or passenger car type tires are different. ST type tires are rated for about 15% greater load capacity, depending on the specific size, but with a max speed of 65 mph.  So if you never exceed 65 mph, ST type is "better" as they are rated for higher load.

BUT

DOT testing for LT type tires is more substantial (more difficult) and has more requirements than the requirements for ST type tires. So if you believe that being able to pass more difficult tests indicates a "better" tire and you want better durability then LT tires are better.

Now if you want to compare two different size or different Load Range tires but the same load capacity then IMO most LT tires are probably better than most ST type tires based on their ability to pass the more difficult DOT tests which are based on load. 

BUT

What if you consider lower-cost your "measure" when comparing tires you might find that many ST type tires have a lower price than many LT type tires.

##RVT910


Thursday, August 8, 2019

How old is too old ?

For RV application this is a tough question, because "It Depends".

Primary factors that affect the answer include 1. Type of RV -Motorhome, tandem axle trailer or single axle trailer.   2.Cumulative temperature i.e. How much time with tires below 60F  Below 70F,  below 80F  below 90F  Above 90F, Above 100F, etc up to Above 140F     3. Actual Reserve Load   4  If a trailer, how many times you backed into a parking spot  5. Do you use white tire covers or is the RV parked in full shade?

Ya, a lot to consider but each of the above items can shorten tire "life".  Would it be possible to construct a formula or spreadsheet with answers to the above to calculate the answer?  Yes but I doubt it would be worth the effort as the life of one brand or size would probably end up with different detailed factors. So let's just consider some of the items I listed so you may gain a better understanding of "tire life"

#1 Type of RV. This is where "Interply Shear" (a force that is trying to tear the belts off the body of a radial tire) Based on computer simulation this shear or tearing force is 20% or greater in tires applied to multi-axle trailers than if the same tire was applied to a motorhome, even with identical weight.  For those that care there are a number of posts on IPS on my blog if you really want to understand the background and how this force affects tires.

#2 Heat. This is the number one "killer" of tires if we set aside the obvious failures due to loss of air pressure. In fact, even the loss of air pressure results in excess heat that can lead to rubber reversion or even melting of body cord which leads to many "Blowouts".  Heat damage is cumulative and has a MAJOR effect on tire life. The reason for this is that rubber is always "curing". In technical terms, this means the molecules of Carbon and Sulfer are continuously linking, although at a slower rate when relatively cool 70F and below and the rate of chemical reaction doubles with each increase in temperature of 18F. I have a number of links to Scientific papers on the chemistry of tire curing in THIS post. It is also important to understand that the hottest area of a tire can not be measured with a heat "gun" or even with TPMS. Here is a graphic showing the relative temperature in different areas of a tire. The internal red area can be 20°F hotter than the rubber just 3/8" away and the range of temperatures in this example is 80°F so measuring at the correct location is critical as well as very difficult as it takes specialized needle probes.
 Also, this is the location of the highest level of Interply Shear.




#3 Reserve Load  This is the difference between a tire's load capacity at the cold inflation number in the tables vs the actual measured load on a tire.  Greater reserve load means cooler running temperature. See #2 above

#4 Backing into a parking space. This is something few think about but in extreme cases, the interply shear might get to 100% higher in a tandem axle trailer when doing a tight turn into a parking space. This high tearing force can initiate cracks in the rubber which can just grow and they never "heal) which can lead to belt separation many hundreds or thousands of miles later.

#5 Tire Covers.  See my post on using white tire covers.  Yes, this simply goes back to cumulative heat. See #2 above.

Long term readers of my may remember my post on how to maximize tire life.

One thing that is true is that Michelin and some other tire companies have set 10 years at the maximum life of a tire no matter what it looks like. This does not mean that no tire will fail due to "age" or the cumulative effects of the conditions I have outlined above. All of these conditions simply are shortening tire life from 10 years down to maybe as little as one or two years in extreme cases.

##RVT909

Friday, August 2, 2019

What's a good Tire Pressure Monitor System for a Class-A?

Had this question asked on an RV forum I monitor. Thought I would share my answer.
+++++++++++++++
While I don't have a Class-A, other than the length, I'm not sure if any one system is significantly better than another. As long as the system you buy can handle the total number of tires on your coach + toad AND is rated for your tire pressure. Warranty length and service may be the only meaningful difference between some units.
I have done what I think is the only direct real-life comparison of internal vs external system back in 2018 and published the results on my blog.
But some general observations and comments.
IMO User-replaceable batteries are a plus. You can confirm the battery P/N before purchase and check at a grocery store or at Home Depot or Lowes for both price & availability but most are under $2 each and last 1 to 2 years depending on use.  I have found that after 8 to 18 months use, low battery power may contribute to the dropped signal. My solution is to mark the install month year date with Sharpie.
I do like a system with long (Lifetime?) warranty and one that actually has the dealer/distributor attend RV conventions as that means they have people that are not just selling "widgets" on Amazon and probably have a telephone, email, and website.
RE: Repeater. I have listened to the "sales-pitch" from a number of different vendors at FMCA Convention and most will ask about the type & length of coach and offer suggestion to get a repeater or not but I also note that some will offer to send a repeater for just the cost of the repeater if you discover you need one later. Others just include a repeater with all sales just ask and see what they say or offer.
Alarms going off. I have a blog post on how I set my TPMS and haven't had any false alarms with the TireTraker system I purchased in 2009 (I did upgrade to the TT500 in 2018 after I killed the original TT400 monitor by connecting the wrong charger to it. My error not TT)
I have found I do not need a power cord to the monitor on the dash as a single overnight charge is good for weeks of daytime use.
I do shut off the monitor each evening. In the morning I turn it on again and by the time I am done with my coffee all 6 sensors have sent in the baseline pressure so I get a fresh "cold" pressure reading just to keep an eye on things. Do not be confused with the time to establish a signal. As far as I know, sensors only send a signal once every 8 to 15 minutes to conserve battery life. They also will send a Low-Pressure warning within 2 to 4 seconds. Read the literature or ask the dealer to learn what your system timing is.
Maintenance:  I do run a "test" every year to confirm the sensors are still reporting air loss in the first few seconds. The post also covers spare parts I keep on hand.

##RVT908