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Thursday, August 18, 2011

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.


  1. Very interesting post, Roger. Thanks for the info.

  2. Is this Rolling Resistance Coefficient available to me as a consumer and if it is where would I look for it?

  3. Pat R.R.C. is used within the industry and requires special corrilation testing to compare the results from one test machine to another. As such it would be misleading to try and compare the RRC of a Michelin vs a Goodyear.

    There is talk of a standardized test to rate fuel efficiency but this would probably be a simpls 5 star type rating.


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