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

Better Fuel Economy for Class-A

Smartway is a program from the EPA that is supposed to help truckers select tires that have better Rolling Resistance (the way tires can be measured) for better fuel economy.

Review the information provided and you will see that most truck/bus tire companies have a line of tires available that meet the Smartway standards.

Will selecting one of these tires get you 20 mpg on your 40' DP  No it won't but it might get you a 5% improvement which could be like getting $ 0.15 off a gallon of fuel which
I bet anyone would like.

While we are on the topic of fuel economy here are some tips from RVTechLibrary


ß Every 2% reduction in aerodynamic drag results in approximately 1% improvement
in fuel economy.
ß Above 55 mph, each 1 mph increase in vehicle speed decreases fuel economy by
0.1 mpg.
ß Worn tires provide better fuel economy than new tires, up to 7% better fuel economy.

ß Ribbed tires on the drive axles provide 2–4% better fuel economy than lugged tires.
ß Every 10 psi that a tire is underinflated reduces fuel economy by 1%.

ß Tires make biggest difference in mpg below around 50 mph; aerodynamics is the
most important factor over around 50 mph.
ß The most efficient drivers get about 30% better fuel economy than the least efficient
drivers.
ß Idle time is costly. Every hour of idle time in a long-haul operation can decrease fuel
efficiency by 1%.

How to get better MPG in your Class-A

While responding to an RV forum question on tire performance for Class-A size tires, I found a potentially very useful web site for those in the market for new tires for Class-A RVs i.e. 22.5" sizes.

The EPA has a program called SmartWay that many may not be aware of. This program identifies tires that can provide better fuel economy than tires not on the list.

Here is the web site with the tire brand and design name of tires that are certified as meeting the minimum requirements of this regulation. Being on this list vs not being on the list is about the only tool available to tire owners to compare tires where claims have been made about improved fuel economy.

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Save money at the fuel pump

Tire Pressure.
 Ya, we tire engineers are like a broken record when it comes to tire pressure.Tire Pressure Monitor System. If you don't have a TPMS then we tell you to check your pressure every morning you are traveling.

We tell you you need to monitor it all the time by using a
We also want you to get your RV weighed then to consult some confusing tables to learn how much pressure is needed for your motorhome.
To make things worse we expect you to have an accurate gauge but then we don't tell you how to check your gauge to be sure it is accurate, or even why its important to have an accurate gauge.

Is that what's bothering you bunkie??

Well this post is going to help answer your questions, solve the problem of how to be sure your gauge is sufficiently accurate and to top it off tell you that its possible that many of you will end up saving more money than the "fix" costs.

To start off lets take a look at accuracy of gauges many RV owners are using today.
In a previous post I showed the results of a series of gauge tests conducted at an RV Rally Sept 2012 on 11 gauges, we saw that there was a 45% failure rate. This was higher than the failure rate seen on a similar sample from 2011 when 11% failed. This year my test sample was 24 gauges and we had a 12.5% failure rate. Failure is defined as more than 5% off when compared to a certified digital gauge that reads to the nearest 0.5 psi. For all these tests the test pressure was between 77 and 95 psi.

According to sources there is a range of fuel economy savings possible from keeping your tires properly inflated because tires are only one of the contributors to fuel consumption. Also different tires have different affects on fuel economy based on a number of variables. Some of these include different rubber compounds, basic tire construction features, tread design and tread depth. Without getting technical we learn that the impact of lower inflation on mpg ranges from  0.05% to 0.3% per psi. Now you may say this isn't much but lets look at how this hits you in your pocketbook

Assume fuel is $4.00 a gal when you do a fill-up. Lets look at the range of savings at -2psi and -10psi from our goal of 100psi (our cold inflation to carry the load with a built in +5psi safety factor). With a 30 gal fill-up the range of "extra cost" for being low on inflation is between $0.12 to $3.60. If you do a 70 gal fill-up running low on air is costing you an extra $0.28 to $8.40 for that fill-up. Remember this is from just being 10 psi low on your tires. A number of the gauges we tested had the owners running from 9 to 18 psi low so they were wasting some real cash.

With this much potential loss from your pocket each fill-up you certainly do not want your pressure gauge to be giving you wrong readings. Having an accurate gauge is easy and based on the above calculations you might save enough in a few tanks of fuel to pay for what you need.

A quick search for "Digital tire gauges" at Amazon. shows you could spend well over $300 for a digital gauge but that really isn't necessary. You can get a good digital gauge for less than $10. This becomes your "Master Gauge" Then you get a second gauge for every day use. When the gauges are new you compare them and they should give the same reading. If you notice a sudden change in tire inflation pressure you can dig out your master gauge and confirm. You should also do a comparison at least a few times a year. The chances of both gauges going bad the same amount at the same time is vanishingly small.

Finally don't just throw your master gauge in the bottom of your tool box. I suggest you keep it in a safe place that offers some type for protection.

Adjust tire pressure for better ride?

Got a question from Bob G. from somewhere in TX 

"Roger,
Let me start off by saying I have really enjoyed your informative articles on the Internet.  Your writing style is one that even the inexperienced can understand and learn from.  Keep up the good work, we need the help!

My question deals with inflation pressures.  I know in the past we have been instructed to inflate according to the manufactures weight limit charts.  With all the tire monitors giving us "instant" pressure readings could the cold inflation numbers be modified slightly where the manufacturer
Inflation Number is achieved after the tires warm up?  I know the NASCAR guys do this.

The real reason I am asking about this is a problem I currently have with "expansion joints" on the highway.  We are currently in the middle of a TX-AK-TX trip and my fillings are starting to fall out!  If my front pressure is set at a cold pressure of 75, which is chart recommended for my axle loading, the bump from expansion joints can be tolerated.  As the tires heat up and pressure goes to 85 and above the bump becomes more of a BANG which hits the front end so hard my dash has broken mounting screws in the past.  Now that I have secured it to the chassis the dash is developing a horizontal crack.  With the aid of my TPMS  I could adjust my cold pressure to reach 75 or 80 hot pressure after a few warmup miles on the tires.  I am currently seeing a temperature rise of 60 to 70 degrees above ambient between cold and hot tires.  This reading was taken with a laser temp gauge measuring in a valley between the tread.  I don't rely on myTPMS for accurate temp as it is a TireMinder with the screw on sensors.

I know I could change my shocks to something softer on the compression stroke to take care of the "bang" but my ride and handling characteristics are really good everywhere else.

What say Ye Great Tire Zen Master?
Bob G"

 

Thanks for the compliment Bob, and for reading the blog.

You pose a reasonable question Bob, but you fail to understand that the load/inflation tables are based on the fact that the pressure does increase as a tire is run. 

If you were to lower your “hot pressure” to match the inflation in the table you would probably soon experience tire durability problems and certainly see a hit in fuel costs and your rolling resistance, which is the force it takes to roll a loaded tire down the road, would immediately increase.

If you are seeing 60 to 70 degree increase over ambient you may be running right at the low limit for tire inflation. You didn’t say how old or what size your RV was or the number of miles on it but shock absorbers do wear out and many times even when the RV is new there are better riding shocks available than the low cost ones that might have been selected by the RV manufacturer.

You are correct about the temperature information from your external TPMS. The temperature you are seeing will most certainly not reflect the tire internal temperature. Watch my blog as I am conducting a test right now to collect the facts. I hope to post the report soon.

Bottom Line

Never bleed down hot pressure. You should consider the inflation on the load tables to be your minimum cold inflation. I usually recommend people run plus 10 % over the table long as they are not exceeding the inflation molded on the tire or the max inflation rating for the wheel. If you can’t run the +10% then you probably have tires and wheels that are lower capacity than what you need based on your actual loading.

Tires - Dull or Dynamic? part one

Following is an article I was asked to write for a tire industry trade publication in the UK. “Tyres International.” I thought you might find it a bit interesting.

“To the untrained eye it might seem like the tire industry has not done much to improve John Dunlop's original. But looks can be deceiving.

Many people think the tires on their car are just a necessary evil. Most seldom, if ever check their inflation while alignment is something few ever consider. Then after 40,000 miles, they complain about the fact they have to buy new tires. Even within the automotive industry, there are those who don't appreciate the dynamic nature of tire design, and the significant improvements and changes made since John Dunlop invented the forerunner of today's modem tire.

There are many challenges facing the tire engineer today, but one of the most challenging is to make continual improvements in rolling resistance. In North America, the Original Equipment Manufacturers, otherwise known as "Detroit", demand the improvement or lowering of the rolling resistance value of the tires they approve. The rolling resistance of tires has a direct impact on the fuel economy of the vehicle. Many would think the primary reason for an interest in rolling resistance would be to allow the manufacturer to advertise good gas mileage for their vehicles.

Stopping the gas guzzle
While good fuel economy is something that can be advertised, a more concrete example of why this is a major concern of the OEM is the avoidance of what is known as the "Fuel Guzzler Tax". This tax can amount to many tens of millions of dollars as the OEM must pay for each 0.10 mpg their vehicles are over a government mandated rating.

There is some data that shows that a one per cent reduction in rolling resistance could be worth US$60 million on certain car lines. Despite this major interest by Detroit, I have never been asked about the rolling resistance of a brand or line of tires by any individual considering the purchase of a set of tires.

Significant strides have been made in improving the rolling resistance of tires going to Detroit. Figure 1 shows the trend as well as the ultimate value possible with a steel wheel on steel rail. It is obvious to see the majority of improvements have already been made and while we may expect some level of continual improvement, we will not see the dramatic improvements of the past 20 years continue in the future.
RRC or Rolling Resistance Coefficient is one way of comparing a variety of sizes and adjusting for vehicle load as well.


Figure 1


Pricing opens the purse strings
At the same time as these improvements have been made and despite great strides in ride quality, crisper handling, improved snow and wet traction and other various measures of performance, Detroit also expects us to lower our price a few per cent each and every year. The fact that many people are willing to spend more for shoes, simply because some athlete wears the same brand, than they are willing to spend on a tire points out the level of disdain and disinterest most feel toward tires. Seldom does a driver consider that it is the tires that must deliver strong performance in emergencies to help protect them and their family from harm.

History in the making
A quick look at the advancements in tires during just the last 80 years can be very instructive. In 1920. your normal auto-mobile tires cost between US$25 and US$60 each. This tire was advertised as being capable of delivering 6,000 miles. This translates to about US$0.007 per mile. With normal inflation considered, these sale prices translate to US$200 to US$500 per tire in today's dollars. When we consider that today's normal tire is capable of delivering 40,000 miles, yet can be purchased for about US$70, we can see that the cost per mile is now only US$0.0018 per mile.”

We will conclude this article in the next post.

Gage Accuracy, Rotation, Alignment, Fuel Economy

Went back and tried to review comments and questions. I know some have been answered in depth but some others maybe not enough to make the point clear so here are some short replies and thoughts.

May 15 Quampers asked about tire gauge accuracy.
Quampers, I currently travel with two digital gages that are accurate to 0.5 psi when compared to ISO certified pressure gauge in a tire testing lab. I can compare readings between these two gages and as long as they are within 1.0 psi or less of each other I can be pretty confident they are still giving me the correct pressure. I will have the gages checked on a two year cycle even if I find no change in their readings. These are the gages I will use to compare to others at my Tire Basics seminars. FMCA at Madison, WI Aug 11 and at Gypsy Journal Rally at Celina, Ohio Sept 27.

June 25 Tom asked about tire rotation and where to put the newer tires if you don't buy a complete set.
I have heard it said by others that if you don’t have a problem with irregular wear on your RV you don’t need to do an alignment or rotate tires. I guess that may be true as long as 1. The manufacturer of the coach bothered to do an alignment at the end of the assembly line and 2. You keep a close eye on the wear of your tires.
Now I can tell you that in my experience it appears that some manufacturers may be cutting corners when it comes to spending the time to set the alignment. After all your warranty is only good for a year and in that time most RV drivers will not get enough miles on their tires to see alignment problems. The second point is that even if you do complain the mfg will probably tell you it is your responsibility to ensure the coach or trailer is in align, even though there is no mention that as a new owner one of the first things you would need to do is to drive your new rig to a heavy duty alignment shop and do the work the manufacturer should have done in the first place.
When it comes to the question of where to place the new tires there are a couple of things you must consider. If your RV has dual tire position you need to be sure the Outside Circumference difference on a pair of tires in dual position is ¾” or less otherwise there will be more load transfer from one tire to the other than is advisable. Not Outside Diameter buy OC which is a more accurate measurement to get if you don’t have special tools. So for Tom it will depend on how many tires he needs to replace as to where they go.
When I recently rotated my tires because of miss alignment on fronts.
They looked like this in inner shoulder and this on outside shoulder













I measured all seven tires (including spare) then put the most worn tire as the new spare. It worked out that the still new original spare ended up on the front and I was able to match my duals to within ¼” for each pair.

Now if we are talking about a passenger car the two new tires should go on the rear to give you better wet traction and decrease the potential of a rotating skid and spin-out in an emergency. This is less of an issue for heavy RVs due to the weight cutting through the water better.
On multi axle trailers I would put the new tires on the front as this location is less likely to suffer a puncture and if you are going to lose a tire due to puncture I would rather lose the older tire. Hope this didn't confuse too many people. As you can see there are a number of things that need to be considered.


June 29 Bob asked about LRR or Low Rolling Resistance
LRR spec tires are designed to trade off a number of performance characteristics to improve fuel economy. Rolling Resistance is the force it takes to roll a tire under load. The more force the more energy needed to make the vehicle go down the road. I have not heard of LRR tires in RV sizes yet as most of this work is aimed at Hybrid cars getting 40 MPG or more.