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Friday, July 23, 2021

Is better tire wear AND better fuel Economy possible?

 We all see posts from people wanting better tire wear and better fuel economy. Here is some information from a friend "Dr. Joe"

Wear, traction and rolling resistance are interrelated (but adjustable) factors determined mostly by tread material properties fixed during the design stage of tire development. The rubber chemist's enduring dilemma has been that enhancing one tread attribute influences the other two – usually adversely. Marketing professionals tend to use the term “balance” rather than “tradeoffs” to describe these conflicting variables. Based on my reading of recent industry press releases, tire wear and traction seem to be playing “second fiddle” to rolling resistance in today’s push for “greener” tires – even though fuel efficiency has not been a top priority for US consumers. It is, however, well known that good tread wear resistance is important to motorists purchasing replacement tires. Contrarily, because of CAFE mandates, OEMs consider tread life subordinate to rolling friction in their procurement of new car tires. Unarguably, any decrease in wear out mileage increases the frequency of tire replacement and unwelcome scrap generation.
Tire traction, nonetheless, is important to safety conscious motorists; it is constrained by road conditions which control traction limits encountered by given tread compounds and patterns. These can be optimized for wet, dry or snow performance. While over 80% of tires in service in the US are rated at the UTQG traction level “A”, only 15% are rated at the highest level “AA”. Surprisingly, no real-world data exists indicating that tires with higher rated traction grades are less involved in highway accidents than lower rated ones – with snow tires an exception as they are not UTQG rated, For improved all-weather traction, so-called “rain tires” have been touted on-and- off over the decades, and promoted extensively by U. S. Rubber (now Uniroyal) beginning in 1965. Wet grip was achieved, then and now, by sacrificing tread wear. While this is an acceptable trade-off in Europe, US consumers have consistently rated long tire life more important than tire grip; and with relatively cheap fuel, rolling resistance tends to be a non-issue for individual tire buyers. The most common reasons reported by the influential Consumer Reports (2019) for selecting a particular replacement tire brand are price (44%), tread life (40%) and brand trust (31%). Similarly, the respected J. D. Power new car owner survey (2021) rates the top three tire satisfaction metrics as wear, ride and traction (in order of importance).

Regarding tread life, surveys of large numbers of scrapped consumer tires usually show that the majority are three to four years old when replaced. Since Americans drive between 11,000-12,000 miles per year on average (according to FHWA), this means that most passenger car tire wearout mileages occur between 33,000-48,000 miles. If light vehicle tire lifespans could be increased an additional year, demand for new tires would be reduced with lessened environmental impact. Also, tires become more fuel efficient as they wear. I wonder what an environmental and economic cost-benefit analysis of tire life extension might yield? Mainly due to existing and proposed government mandates, US consumers have been, or will be, forced to unwittingly accept reductions in tire life with increased costs in concert with lower rolling resistance. Then we encounter further demands placed on EV tires – which need improvements in tread wear, traction, and rolling resistance compared to their ICE powered counterparts. Additionally, the
California Energy Commission once again announced plans to implement a program to ensure that replacement tires sold in that state are as energy efficient as OE tires. This will only exacerbate the confounding situation facing consumers valuing tire life.
Ponder Michelin’s
transitional development of the radial tire after WWII. Wearout mileages were doubled while rolling friction was reduced by 25% compared to existing cross-ply tires. Could the industry now develop tread compounds and/or tire constructions that at least make desirable improvements in both wear and rolling resistance without comprising grip? Unexpectedly, Bridgestone, Arlanxeo and Solvay have just announced material technology that claims to achieve just that; up to 30 percent better wear efficiency and six percent reductions in rolling
friction. Hopefully, this technology will be licensed to others if the claims are justified
.


Joe Walter enjoys teaching Vehicle Dynamics and subjects related to tire materials and mechanics at The University of Akron. He previously served as Vice President and Director of Bridgestone Americas Research Center in Akron and President of its European Technical Center in Rome. Joe obtained graduate and undergraduate degrees in engineering from Virginia Tech a long time ago.

While Dr. Joe's article is aimed at the passenger and light truck vehicle market you can be assured that as new technologies are developed in one sector of tire design the features and advantages soon spread to other product lines. 

##RVT1010

Friday, July 16, 2021

Airless tires? Reality? or just a pipe dream for RV owners

 A friend recently sent me a copy of an article from the Akron, Ohio daily paper The Beacon Journal.


 I am in Colorado, ending a 3 week working (giving tire seminars) trip, and celebrating with my wife, our 37th Anniversary sightseeing vacation, so missed the article on "Airless" tires. 

 

Wait! 

 

 What do they mean "Airless"? Could we soon be absolved of needing TPMS in our wheels? What will I write about if I can't keep complaining about people not using the proper inflation?

This sounds too good to be true. Well it is true...Sort of. It appears that the latest effort from Goodyear to develop a reliable airless tire is aimed at some "self-driving" vehicles that can transport goods and maybe even people around a small ares of a town or city.

While air filled "Pneumatic" tires have been around since 1847, the background on "Airless tires" is many decades old with many tire companies all trying to be the first to crack to code and present a reliable tire that can function like a regular tire when inflated with air. So far everyone seems to run into the same wall of limited speed or limited durability. While Goodyear hasn't released any specifics, visually their latest effort "resembles similar products being tested by other companies in its open-spoke design and flat tread" according to the picture (above) from the press release and an article in Rubber & Plastics News.

There are many "Airless" tires already in use today. In fact, in 1972, I worked on the Flat-Proof tires for the then brand new Dallas-Ft Worth airport for their passenger transfer system of driver-less vehicles that circulated the airport.  The tires had no air inflation but were filled with a heavy duty "foam-rubber". Other applications of airless tires include lawn mowers and numerous construction vehicles.

 If you wanted, you could order some Airless tires today for your forklift truck and would never need to add air or worry about the tires being punctured and going flat.

One thing that is almost universal with these applications is that they all have significant restrictions on operation speed, This limit is usually below 20 mph and if operation at this speed is required, the distance traveled or even the roadway used  must be strictly controlled.

So, it looks like we RV folks need to continue to wait for the scientific breakthrough that is needed to put tires on our cars, truck , trailers and RVs that no longer need air inflation to carry the load.

##RVT1009

Friday, July 9, 2021

Should you use the inflation that is listed on the tire sidewall?

 Many RV owners do not understand the inflation and load information that is molded on the sidewall of the tires they own.  As a tire design engineer, part of my responsibility was to specify all the words, symbols and numbers on the tire sidewalls. Some of the words such as brand name like as Goodyear or Michelin and the "line"  like  "Eagle" or "Transforce" are obviously selected by the sales and marketing departments. 

The tire size or sizes had been selected and it was my job to design and request molds appropriate for the sizes that were to be part of the new line of tires. For each size, I needed to consult the US Tire & Rim Association data book and to specify the appropriate load and inflation numbers for the maximum allowable for the Load Range of each tire. With LT lines we might have LR-C, LR-D and LR-E tires and if incorrect numbers ended up on the tires they would need to be recalled and replaced for free so it was obvious that this information had to be correct.

With the exception of a few tires that are designed for a new model of a specific car or Light Truck from Ford, GM, Toyota, M-B etc, I would never know what vehicle the tires would end up being mounted on so there would be no way for me to specify a specific load or inflation for any given tire that was vehicle specific. Selecting the tire and Load Range and specifying the inflation number to be posted on the vehicle Certification label is, by regulation, the responsibility of the vehicle manufacturer. It was however my responsibility to ensure the tire was capable of passing the DOT tests as well as company minimums based on the use of industry standard loads and inflation numbers.

All tires have a Maximum Load capacity molded on the tire sidewall along with the minimum inflation needed to support that load.

With this background information I hope you now understand that the inflation number molded on the tire sidewall is not selected or made up by the tire engineer as the inflation number comes from the published Industry standards. The inflation on the Certification Label aka Tire Placard is specified by the RV manufacturer and by federal Regulation must be sufficient to support the GAWR (Gross Axle Weight Rating) which is part of the RV company design process.

The placard inflation may be equal or less than the number on the tire sidewall but it should never be higher than the tire sidewall pressure number.

Ideally you would have actual scale loads with the RV fully loaded at its expected heaviest. With that load known you can consult the tables to learn the minimum inflation needed to support your load. However if you don't have scale readings the best thing to do is inflate your tires to the placard information. This is OK as long as you have not overloaded your tires. Note that the tables for tires made by Goodyear are the same as for tires made by General, or Firestone, or Bridgestone, or Cooper. Also most Michelin tires have the same numbers as the other tire companies with the exception of a few tires that were originally designed for European country application where metric units are standard. When converting to the US "Inch-Pound" units the numbers do not always match up so if you have Michelin tires you probably need to consult their tables.  You can also check the tables listed on this blog post.

 

If you review the above you will see that I am not advising that you use the inflation on the tire sidewall, unless that is the inflation on your Placard.

A side comment on the inflation number of the tire. The words may be "Max Inflation" on some tires, but this is related to the way loads are established for tires based on the inflation. The LIMIT is the stated maximum load. The intent in the wording is to stress that the tire load can not be increased even if the inflation is increased above the number associated with the tire's "Maximum Load".

Regarding hot tire inflation numbers higher than the number on the tire sidewall, that is OK as long as the set "cold inflation" is not set higher than the number on the tire. Tire inflation will increase when the tire temperature increases. The rate  of change is about 2% for a change of 10F. Seeing your "Hot" inflation higher than the tire sidewall is not a big deal. With the advent of TPMS many people are seeing tire temperature or pressure increase for the first time as a driver. Most TPMS have the high temperature set to 158F.  I have found that setting the high pressure to 125% of your cold set pressure should normally avoid having the alarm sound as long you are not overloading your tire or pushing your driving speed. If you get close you might just drop the speed back a few mph. Personally I set my cruse to 62 or 63 mph and stay in the right lane. I do not get people honking and I get real good fuel economy. (10.2 mpg in my last 1,200 mile trip from Ohio to WY).

 

##RVT1008

Friday, July 2, 2021

Tire Life. Why can't I get a straight and consistent answer?

 Have seen a number of posts on RV forums and Facebook asking why there are different answers to the question of when to replace tires in RV application. Some are told "Replace at 5 years" and hear " you will die if you drive on a 6year old tire.

Discount tire has presented this diagram.

You will note that they do not show some cliff that you fall off.  I responded to a question on tire life where the person thought that the tire companies were simply pushing tire sales.

Tire "Life" is not an on-off switch. Rubber begins to lose its strength and flexibility the day it is put in the tire warehouse. Temperature and time are the primary drivers of the loss of strength and flexibility. Tires can fail for a variety of reasons. Hitting potholes creates cracks in the internal tire structure. Most are microscopic but all cracks grow and none repair themselves so the number and size of cracks simply grow till one day the rubber will not be strong enough to tolerate hitting a pothole or piece of road debris and the heat generated with a long run at high speed on a hot day simply lowers the remaining strength of a tire.

The more a tire is driven the more flexing it experiences. Older tires, having lost some of their flexibility, will experience more actual tearing rather than stretching. Driving faster increases the rubber temperature. The higher the rubber temperature the faster the rubber loses its ability to stretch and recover. 

My post on tire covers pointed out the "aging rate' of tires doubles with each increase in operating temperature of 18 degrees F.

Part of Organic Chemistry is chemical reaction rate.

For every 18F increase in temperature the rate of aging doubles. Heat also comes from being in the sun when parked. So if the RV is parked with tires in direct sunlight you can see the tire achieve 36F increase or more which means it is aging at more than four times the rate it would have if in full shade.
If you want to understand the technology behind this accelerated aging due to heat I suggest you can read some of these sources if you have a few hours.
http://en.wikipedia.org/wiki/Reaction_rate

http://chemistry.about.com/od/stoich...actionrate.htm

Here are some specific references on tires
http://www.rubberchemtechnol.org/doi...5254/1.3547913

 

The idea that tires be replaced after 5 years of use is based on probability. Some tires fail at 3 years of use and some are still running after 9 but it's the odds that can get you. If you have an RV trailer I can assure you that the science shows that backing into an RV site is much harder on the tires than pulling through. This is because the Interply Shear is much higher backing in because the side forces are much higher. I wrote about that force in this blog post. https://www.rvtiresafety.net/2018/09/warning-super-technical-post-tire.

 

##RVT1007