Does any tire company have some "Magic Rubber:?

 In Sept 2024 I wrote on the Operational limits on ST type tires. I suggested that the published 65 MPH was a realistic compromise but apparently many people think they can get tires with some "Magic Rubber" in them so I am again writing about the "Speed Rating" of ST type tires.

 In the US "Speed Rating" is really a measure of tolerance for high heat and is based on a 10-minute long test with speed increasing every 10 minutes till the tire fails. In Europe, Asia and the rest of the world, they do not offer an ST type tire because their speed tests are more realistic and stringent.

When ST type tires were introduced to the US market some 45 years ago, they were given a higher load capacity rating than a same-size LT tire BUT the trade-off was STATED in the industry standards books as having a max operating speed of 65 mph. With 50 years of Tire design and testing under my belt, I know of no "Magic" rubber that will deliver greater load capacity for a given size and inflation without some trade-off.

There are only 5 variables that control operation speed. Size, Load, Inflation, speed and the ability to be rated for operation with passengers in the vehicle, so unless you invent some "magic rubber" you are limited by physics. Yes, materials have improved over the last 40 years after the switch to Radial construction and we have seen improvements in tire performance, but have you ever asked why a company can make a tire of the same physical size and same load capacity at a given inflation and somehow make one tire carry significantly more load than the other without some trade-off in operation speed?

If I had invented some "Super Magic Rubber" for ST type tires that gave them "Super Strength" why wouldn't I put the Super Rubber in the other tires I make and sell and take over the worldwide tire market? Any company can ignore reality and make a marketing decision and claim a "Speed Rating".

 

At what temperature reading of TPMS should I worry?

 Read a forum post with a question

 Hi all, very newbie here.

I have a 1/2 ton double axel travel trailer with ST225/75 R15E Goodyear Endurance Tires on it. I was  towing it today and my TPMS monitor alarmed because of tire temperature.

Now nothing extravagant, tires were between 75 and 82 PSI, running temps for all were not above 85 degrees.

The TPMS was at factory settings. I found this on the internet, this guy says 158 degrees is a standard alarm trigger for TPMS. Is there a critical do-not-exceed tire temperature?  What should I set the temperature tolerances at in the TPMS so it is not alarming with basic driving?

 

 Here is my response

 As an actual tire design engineer  who has been working with TPMS since 2002 I can suggest that you not worry about the "High Temp" warning as it is normally set to 158F. You need to pay attention to the PSI. I suggest the low pressure warning be set to the minimum psi required to support your MEASURED inflation level. I suggest that you never operate the tire in overload. TPMS Temperature is not reporting the hot spot of the tire as that point is located about 1/4" to 3/8" inside the shoulder of the tire. Rubber is an insulator so it does not transmit the heat energy to the tire inside air, TPMS temperature readings are closer to the temperature of the metal wheel, hub and wheel bearings as the metal does transmit the heat of these metal parts quickly. A high Temp reading from the TPMS without a significant increase in PSI is probably warning of a wheel bearing problem.

What is the proper inflation for my tow vehicle and RV trailer tires?

 

I monitor a number of RV forums and when I see someone asking about tires, I make the effort to learn about the problem and offer solutions, if possible.

Recently there was a question on inflation for both the tow vehicle and the travel trailer. The comments seemed to be all over the place, so I decided there was a need for some basic foundation of information. Following is my reply and attempt to provide the basic information needed by RV owners.

Tow vehicle (TV)

Tire size, type and inflation should go by the Certification Sticker on the driver door jamb. This was established by a team of tire and vehicle suspension engineers over a period of two to four years. There were numerous changes and tests run on different specification and performance parameters that were fine-tuned to meet the goals of the vehicle design team. The sticker provides a recommended inflation that normally delivers 25% to 35% Reserve Load, so those numbers should be followed unless you have done a lot of research and understand the trade-offs. Do not forget that few people in the tire store have technical training beyond how to sell tires, so I would be careful with the information they provide.

Travel trailers (TT)

Tires for almost all RV trailers have a single spec—that being Low Cost. I have never heard of any vehicle testing or evaluation that compares different tire constructions or ratings for the application of a tire to the travel trailer.

To achieve low cost, tires are only required to meet a single requirement: that they meet the minimum load capacity specification needed to support the RV. In 2017, the RV Industry Association (RVIA) established a Reserve Load of 10%, but for RVs built before 2017 there was no Reserve Load requirement.

Those of you who have read the owner's manual and reviewed the Certification Label information and the Load and Inflation information molded on the tire sidewall may have noted that for most RV applications, you can only achieve the tire's 10% Reserve Load capacity when inflated to the level required for the  maximum load capacity.

Yes, this basically means you must run the max inflation for the tire's Load Range if you want to have the minimum margin of Reserve Load recommended by the RV Industry Association.

Tire type nomenclature

In the subject post there was some confusion about the Michelin "LTX" line. One poster thought this was some special "Hybrid" type of tire, so I feel the need to clarify tire "TYPE" nomenclature.

The letters before the numbers in the tire size are critical and important but too often people seem to ignore that important info. The P is for Passenger, LT is Light Truck, and ST is Special Trailer. ST should only be used on trailers and are not approved for use on motor vehicles that carry people. if a P type is applied to a trailer, its load capacity MUST be reduced by dividing the load capacity stated on the tire or in the Load & Inflation tables by 1.10. But if an LT tire is applied to a trailer no reduction in load capacity is required.

Eventually, the following information was added to the Forum thread:

------------------ Steer Axle ---Drive Axle --- Trailer
Weight #1 - Truck only/hitch/bars -- 3180 3520
Weight #2 - Truck and Trailer with WDH bars -- 2980 4320 4880

Side note: The owner had previously stated the TV GVWR was 6500, so his scale reading on the initial weighing seems to exceed his GVWR !

I am assuming the "Trailer" scale was for the four tires on the RV. If so, it sounds like the trailer was empty when he did the weighing.

In the thread, I also saw a comment about Michelin tires. The owner said:

It was helpful to learn of both the Michelin "hybrid" LTX and the Cooper XL alternatives to LT tires although when I looked up the Michelin LTX I saw that it comes in A/T and A/S versions ... even more confusion ... is the A/S the "hybrid" and the A/T the real LT??

My response

I'm not sure what you mean by "Hybrid". Michelin has a "line" of tires it calls "LTX"— this includes both passenger type and LT type tires. Think of this as with General Motors, which has a "line" of cars called Chevrolet with many type vehicles from sedans to SUV and pickups.

In my post I covered the three basic families of consumer tires: Passenger, Light Truck and Special Trailer. Each "family" has many different sizes and many different tread patterns, like the A/T, that is a traction tread pattern, and the A/S which is All Season and provides less off road or snow traction.

Load Capacity

There are also within each family different levels of Load Capacity.

P type "family" tires come in "Standard Load", that has no special markings, and also XL for Extra Load.

LT and ST "families" have greater load capacities, so they have letters assigned to the "Load Range", or LR for short, with the different LR having letters starting at C, D, E and on up in some brands. Each letter has a specific maximum load capacity at a specific inflation. The load capacity is published in tables available in some owner's manuals or tire data books, or even on the internet.

All of the above applies to tires made to U.S. Tire & Rim Association standards. Europe has some similar but different standards with different codes, as does Asia. I will not go into those standards, as I probably have already overloaded you with the above.

Clearly, the owner of the truck and trailer needs to learn more facts about tires and proper loading of his TV truck.