At another point, this same expert engaged in this exchenge:

Question. Is it generally the aim of the tire manufacturers to have their tires put on cars so that they will not normally be driven overloaded?

Their

Answer. I don't think that is a specific alm of the tire manufacturers. specific aim is to sell as many tires as possible.

Question. In other words, they will put ⚫ will be out tires, knowing that they overloaded?

Answer. I think that is correct. They know that a certain percentage of tires that they sell will be exposed to overloading conditions.

The fourth expert to testify in this trial, the veteran chassis design engineer for the automobile manufacturer, was asked how his firm selected a tire to use on a particular car. Do they use the Tire and Rim Association manual, he was asked?

He replied:

We primarily use the Tire & Rim book to determine the maximum size of the tire section we have to put enough room around all of the wheelhouses so that the tire doesn't strike the wheelhouse.

Obviously, the tire is selected for its shape and not for its load-carrying capacity. The plaintiff's attorney pursued this point:

Question. Does General Motors make any attempt to determine the maximum carrying capacity of any tire?

Answer. No we made no attempt whatever to try to determine its maximum, which I believe would be rather difficult. Question. Do you at General Motors ever advise the purchaser of your car the amount of load they can carry in the car without overloading the tires?

Answer. Not to my knowledge.

Question. Would you tell us what you think overloading a tire means?

Answer. I would say that a tire is overloaded when it does not satisfactorily perform its duty.

This top General Motors engineer insisted that the tires supplied with General Motors cars were fully adequate. He described a 35,000-mile test used by General Motors to test its cars and to test new models of tires at the same time. However, he was unable to state whether the kind of tire supplied with the car involved in the lawsuit had actually been

put through this test. He made clear that the tires are tested for qualities such as "ride, stability, and steering feel" and not as to the carrying capacity. If the tires do not fall in this test, they are accepted as adequate. During the 35,000-mile test, the car's load is changed several times to determine performance with differing loads.

The GM engineer testified that in his opinion:

A General Motors tire is not overloaded when it performs satisfactorily in riding, handling, and durability.

Question. That is the only test that General Motors adopta?

Answer. I don't know what other tests there are they are the only tests that I am familiar with in my capacity as a tire engineer with Chevrolet at that time.

He was quizzed as to whether a ninepassenger station wagon could safely carry nine full-sized persons. Although he quarreled some over whether you could fit nine men into a nine-passenger station wagon, he did believe that the tires on such a car would not be overloaded, even if the car was fully loaded with adults despite the fact that this put it well above the maximum tire load ratings indicated in the Tire & Rim Association manual.

But here again, the expert witness who was willing to give assurance that a normal carload of people would not overload the tires was forced to admit that he did not know what load the tires could carry.

Question. How much weight in addition to the maximum recommended by the Tire & Rim Association could those tires carry without being overloaded?

CXII-437-Part 6

Answer. I couldn't give you an actual Agure on that.

Question. You don't know where you could go for that information?

Answer. I don't believe so.

SIGNIFICANCE OF TESTIMONY

Think of the significance which this extensive testimony has for a nation faced with a critical highway safety problem.

We have more than 90 million automobiles on our highways today. It is perfectly legal for them to travel speeds of 60, 70, and, in at least one State, even 80 miles an hour. Cars are bigger, heavfer, and more powerful than ever before. At a time when millions of people are racing about this Nation on highways, we are told by experts in the automobile and tire industries:

That many new cars have overloaded tires when all seats in the car are filled.

That the manufacturers of these tires expect them to rupture if they are driven in an overloaded condition.

That no determination was made as to their load-carrying capacity when these tires were fitted to the car.

That the manufacturer of the car cannot tell the driver of the car what load he may carry without overloading and probably rupturing his tires.

Is there any wonder why thousands of Americans are experiencing tire failure and tragic accidents? Is there any question as to whether millions of American families are speeding across the Nation on top of a time bomb?

The San Francisco trial is the missing link in the story of tire scandal in America. Now we have on record the sworn testimony of the tire and automobile industries' own experts. They concedo that automobiles are being wrecked today, causing death and injury, because overloaded tires are rupturing. They admit that they deliver cars without any regard to the load their tires will carry. And they admit that it is impossible for the motorist to do what they have refused to do-to coinpute the load that an American automobile tire may safely carry.

This is a shocking and scandalous situation and the Congress and the American public should not rest until it is satisfactorily corrected.

BILL S. 2669 DESCRIBED

The bill we are considering today is a sound step toward correcting this scandalous situation. I do not suggest that the bill is a complete answer, but it is certainly a step in the right direction.

I want to commend the chairman of the Senate Commerce Committee, the Senator from Washington [Mr. MAGNUSON] and his staff for the long hours they have devoted to this legislation.

As I indicated earlier, I introduced a very mild tire safety proposal in May 1964. A year ago, I introduced S. 1643, a stricter bill, to require minimum tire safety standards and to establish a tire quality grading and labeling system.

Commerce Committee The Senate held hearings on my tire bill last summer. Those hearings confirmed most of The the fears which we had about tires. committee then made revisions in the bill and reintroduced it as S. 2669 with Chairman MAGNUSON as the author, and I joined as a cosponsor.

With some further revisions, the committee has now sent S. 2669 to the Senatc.

This bill would direct the Secretary of Commerce to establish minimum safety performance standards for tires. The Secretary is to adopt interim standards immediately and to conduct a research and development program over the next 2 years, at which time new and permanent standards are to be established.

These standards will indicate the maximum permissible loads for each size of tire. The Secretary will direct the tire manufacturer to label his tires with accurate and appropriate safety information, such as size, load carrying capacity, and proper inflation pressure. Thus, this bill will:

First. It should completely eliminate from the market the really shoddy, "cheapie," tires which are now offered to the public, often at so-called bargain prices.

Second. It will give the motorist some reliable facts as to size and load-carrying capacity so that he can select a tire to suit his needs and so that he will know what loads he may carry in his car.

Third. Direct the Secretary of Commerce to prescribe a uniform quality grading system for tires within 2 years.

The Federal Trade Commission, in issuing its new guidelines for tire advertising and labeling, said there was an

urgent need for a system of tire quality grading.

I cannot believe that the development of a simple process to help the motorist intelligently choose between different qualities of tires is a monumental task. The Secretary of Commerce could and should develop a tire quality grading system within 1 year.

We should not lead ourselves to believe that we have dealt with our national tire scandal with finality until we have established a system of quality grading for automobile tires.

My concern is that the Commerce Department has shown very little enthusiasm for strong tire legislation. And they have been particularly reluctant to develop a grading system. They openly question the feasibility of such a system-and they maintain that its development presents a complex technical problem which would take years of study. I would like to introduce into the RECORD at this time a grading system for tires developed by Mr. E. J. Heitzman of Princeton University. Mr. Heitzman's impressive résumé is contained in his report. He has been a research engineer at General Motors for the past 8 years. Now he is studying the adoption of aircraft dynamics technology to automobile problems at the Department of Aerospace and Mechanical Sciences at Princeton.

Mr. Heitzman completed this study at the request of Mr. Ralph Nader in approximately 30 days. I have spoken to a number of technical people who are familiar with the report and they all agree that it represents a fine beginning on a grading system.

One of these people, Mr. Irmin Kann, who is doing automobile safety research at the Stevens Institute of Technology, says that there is no doubt that a grading system can be developed within 1 year. The equipment is available now at Stevens and other universities throughout the country. After converting this equipment, which at Stevens I am told would take several months, work could begin immediately on the development of such a system.

This report is solid, technical evidence that a grading system is, in fact, sensible, feasible, and workable. Furthermore, it proves that such a system can be developed in a relatively short time. It is perfectly clear that the Commerce Department, the industry, and appropriate private and public representatives could get together and come up with a meaningful grading system within 1 year.

I ask unanimous consent to have the Automobile Development Associates report on a performance rating system for tire system printed in the RECORD.

There being no objection, the report was ordered to be printed in the RECORD, as follows:

REPORT No. 4-1-A PERFORMANCE

RATING

SYSTEM FOR TIRE SAFETY (Requested by Mr. Ralph Nader. Washington, DC.)

which, in ADA's opinion, importantly affect automobile safety. It was to be capable of providing the buyer of an automobile or of replacement tires sumcient information for an intelligent decision on tire adequacy, and also of forming a basis on which the individual States or the Federal Government might legislate minimum tire standards.

RATING SYSTEM

A nine-digit, three group numerical rating: that is, 098-22-3566 is proposed, which is to be prominently marked on every tire, The along with make, model, size, et cetera. first group of numbers represents rated load to the nearest 10 pounds. For example, 098 equals 980 pounds, 104 equals 1,040 pounds, et cetera. The second group is the pressure for that load rating, so that 098-22 is to be read "980 pounds at an inflation pressure The last of 22 pounds per square inch." four digits are performance indexes, which correspond to individual tests for temperature-load endurance; traction or breaking ability on dry road surfaces; lateral stability, or cornering ability; and wet road perform

Many aspects of tire performance including heat buildup and lateral stability properties, depend to a great degree on a combination of tire pressure and tire load. These two factors are therefore listed first, as "independent variables" for the rating system. This means that the tire manufacturer is free to claim whatever he wants for the "rated" lond; but a high rated load will adversely affect the ratings in the performance categories. From another viewpoint, if the tire manufacturer wants a high rating in the heat endurance, traction, and lateral stability Categories, he will be forced to lower his rated load accordingly. For example, the same tire might conceivably be rated either 095-22-3553 or 080-22-7573.

The pressure for the rated load should be the Intended inflation pressure for the tire. In case of new cars, it should be the car manufacturer's specified pressure.

Ideally, in the case of new cars, the presBure would be the normal pressure specified by car manufacturer, and the load would be that of the heaviest loaded wheel with a full passenger complement and a loaded trunk.

TEMPERATURE-LOAD ENDURANCE

This rating, on a 0-9 scale, should be based on a severe combination of load, ambient temperature, and speed. A good test condi

tion would be 125 percent of rated load (25 percent overload), on a standardized rolling drum of about 7 feet in diameter, with a tangential (linear) speed of 100 miles per hour, in an ambient temperature of 150 degrees Fahrenheit. Tires would be rated on the basis of endurance time under this test condition.

A "zero" rating might be given for 1 hour or less and a "nine" rating for 20 hours or

more.

This rating is important from the safety Aspect because most highspeed tire failures are due to excessive heat buildup, which is caused by speed combined with overload and or underinflation. It is realistic because temperatures in this range, measured over blacktop pavement, are common in many parts of the United States, and car

owners do not typically increase tire pressure when their cars are heavily loaded.

Rolling drum test machines such as that mentioned here have been used by American tire companies since the 1930's.

DRY ROAD BRAKING

Braking or tractive force exerted by a tire is always accompanied by a slipping, or creeping motion within the contact patch between tire and road surface. Because of this motion, the tangential speed V of the tire tread is somewhat less in braking, and greater in traction, than the linear speed V. of the wheel, as shown in figure 1. The quantity (V.-V.)/V. is called slip ratio. With no braking the slip ratio is zero, and with a locked-wheel skid it is equal to unity.

Figure 2 shows the relationship between the braking force (or wheel torque) developed by the tire, and the slip ratio. The force-slip (or torque-slip) characteristic is linear (portion A of the curve in figure 2) up to some slip ratio between 1 and 2, (portion B) at which the available braking force peaks. At higher slip ratios (portion C) the elastic deformation (creep) within the contact patch gradually changes to a sliding motion, the friction changes from "static" to "sliding." and the available force is reduced. (References 1-3.)

The proposed criterion for tire braking ability is the measured shape of this forceslip characteristic, as described later in this section.

A suitable test machine for tire braking performance would consist of a trailer equipped with removable weights for load adjustment, and with brakes controlled by an electrohydraulic servo system. A load cell between the trailer and tow car would be required to record braking force. Blip ratio would be obtained from the difference between the braked wheel speed and that of a free-rolling "fifth wheel."

In operation, the tow car would be run at a fixed speed. The pressure to the brakes would be modulated by the servo value to obtain "command" values of slip ratio. The data recorded would be that of figure 2.

The braking performance of a tire is nominally independent of speed, but it is affected by tread temperature. Because of frictional heating, the braking force will drop somewhat with length of skid (Reference 2.) For this reason, the braking test is best run on a programed time schedule, such that the slip ratio scale of figure 2 is equivalent to a time scale. The time duration in the skidding range will determine the degree of tread heating.

The brake test just described would result in a performance curve like figure 8. This plot presents four criteria for rating the tire's braking ability. These are: the slope of the linear portion A of the curve; the peak force at B; the sliding force at C; and the reduction in sliding force due to tread heating at D. These four criteria can be combined into one by simply taking the area under the curve. This area results in a single criterion which includes all four aspects of braking performance, with extra weighting given to skidding performance. It probably relates quite well to actual stopping ability.

Use of the programed time scale also results in an extremely simple mechanization of the experiment. The area under the force-slip curve is a simple time-integral (average) of the trailer drag force, which can be read on a dial or recorded directly. A description of the mechanization and a block diagram are given in appendix 1.

Because of the simplicity of this test, it is easily carried out on several representative road surfaces, with the results averaged for rating purposes.

Vol. I

CORNERING POWER

Tire cornering performance is the most important factor in the lateral stability of the automobile. A measure of this performance is "cornering power," or side force per unit "alip angle." "Slip angle" is defined as the angle between the plane of the wheel and its direction of motion, as illustrated in figure 4.

The mechanism of side force generation is shown in figure 5. For conceptual purposes, the tire tread is shrunk into a "meridian band," which is a narrow elastic band around the tire circumference at the center of the tread. When a side force is applied, a rolling tire is deflected sideways, so that a slip angle is developed. A point on the meridian line will lie in the center plane of the wheel until it approaches the contact patch between tire and road. It will then be stretched and forced into the direction of wheel travel until it leaves the contact patch and can return to the plane of the wheel.

The side force generated by the tire is the sum of the elastic forces generated by each increment of deformed meridian line length. Mathematically, this is the integral over the length of the incremental elastic force. It is directly proportional to the area under the deflected meridian line projection as shown in figure 8. The line of action of the resultant side force passes through the center of this area. Because of the triangular shape of the elastic curve, the center of area is behind the center of the contact patch, by a The distance known as pneumatic trail. product of side force times pneumatic trail yields a moment, called self-alining torque, which adds to the positive caster effect of the car's suspension.

At large values of slip angle the elastic force on portions near the rear of the tire contact patch exceeds the limit of adhesion and these portions begin to slide, as indicated in figures 5 and 6. As a result of the reduced length of the elastic curve triangle, the side force becomes less than proportional to slip angle. The pneumatic trail also decreases, also at high slip angles the alining torque may become negative.

At very

problems. A rating system should present a fair balance of all these factors.

The proposed rating system is made up of the product of cornering power (side force per unit slip angle) at three degrees slip angle, multiplied by cornering coemcient (side force per unit load) at 20 degrees slip angle. Tests are to be run at rated load and pressure, and at 70 percent rated pressure combined with 125 percent rated load. The two results are to be averaged for the final rating.

These rating tests should be run on actual road surfaces. A suitable test rig could be similar to the Axed-base machine (moving road) used by General Motors Research Laboratories, or the moving-base machine (real roads) used by Cornell Aeronautical Laboratories. An ideal test rig in many respects is a large arm rotating about a vertical axis. This arrangement combines the advantage of both fixed base and moving base machines. Rotating arm machines of 35-foot radius exist at the Davidson Laboratory of Stevens Institute of Technology and at the David Taylor Model Basin. Although designed for towingtank testing of ship models, they might easily be adapted for tire testing.

WET ROAD PERFORMANCE

Both braking and cornering performance of tires are degraded on wet surfaces, to greater or lesser degree, depending on surface roughness and drainage. Wet road performance can be generally divided into two categories: moderately wet surfaces which may become slick; and very wet surfaces on which tires may "hydroplane" at speed. (Refs. 2, 6, 7.)

According to reference 2, performance in the linear range of the brake force-slip ratio and side force-slip angle performance curves is not affected by moderate wetness, at least at low car speeds; however, the asymptotic values at high slip ratios or slip angles are determined by the road surface. This characteristic is shown in figure 11, which is reproduced from reference 2. Tire parameters which affect skid resistance on rough surfaces are primarily load, pressure, and tread rubber compound. On smooth sur

faces the most important tire parameter is "tire drainage," or the ability of the tire tread design to channel water into grooves so that raised portions can "bite."

Tires

When road surfaces become flooded or covered with slush or water, vehicles above some critical speed (which may be as low as 50 miles per hour for passenger cars) encounter the phenomenon of hydroplaning. under hydroplaning conditions become detached from the road surface and their ability to develop braking force or cornering force is almost entirely lost. Physical and mathematical explanation of tire hydroplaning and a description of its effects is given in reference 8.

According to reference 8, hydroplaning tendency is little reduced by increased load, because the tire deflects and its contact patch becomes larger. Hydroplaning tendency is greatly reduced by increased inflation pressure and by tire tread designs which provide good drainage grooves.

Rough-textured pavement surfaces also reduce hydroplaning tendency somewhat by giving the water someplace to go.

According to reference 8, linear as well as nonlinear portions of the brake-slip and cornering force-slip angle curves are affected by hydroplaning.

Tire braking and cornering behaviors are For this reasimilarly affected by wet roads. son, the wet road performance rating can be based on braking tests only.

The wet road rating should reflect the drastic loss in performance under high speed hydroplaning, as well as the more prevalent, but less severe, performance reduction It should also give on normally wet roads. consideration to the various road surfaces encountered in normal driving.

The proposed wet road rating system is based on the same type of test as performed for dry road braking. It should be an average of several braking tests run on different representative road surfaces. This average should be multiplied by the speed at which hydroplaning begins on water-covered concrete to obtain a Anal rating.

DISCUSSION

The tire tests described here are intended to be both comprehensive and fair. They include all factors which are considered to be important to safety, with greater weight given to phenomena which might produce catastrophic results.

No serious attempt has been made to call out specific rating numbers for each test, since further research is needed before this can be done properly. Some mathematical manipulation will be required to give the described test results the proper combination of realism and sensitivity. For example, even a very poor tire will have some area under a braking force-slip ratio curve, and so some "baseline" area will have to be subtracted from the test results to arrive at a realistic zero rating. Then some multiplier will be required, such that an exceedingly good tire is given a rating of six or seven. (Allowance for future technological improvement should be built into the rating system.)

The cornering power, dry road braking. and wet road performance tests could all be carried out in a single test facility, consisting of the rotating arm mentioned on page 10. Different road surfaces could be placed in concentric tracks, so that only the position of the tire along the arm would be changed between tests. In such a fixed indoor facility, controllable wetness of road surface is easy to maintain, and all-weather operation is possible.

With respect to the temperature-load endurance ratings, it might be argued that not everybody drives at 100 miles per hour (some cars won't even go that fast) and so testing at that speed is unnecessarily harsh. The obvious reply is that not every tire need rate very high in that or any category. A person who never goes over 50 miles per hour may be satisfied with a tire having a five rating. In Connecticut or New Jersey a one rating might be acceptable for a car to pass State inspection, while Arizona or Texas might require a minimum of three. The whole point of a rating system is that it gives a basis for intelligent choice; such a basis is not now available.

Nevertheless, since speed is a legitimate tire design parameter, comprehensiveness might require categorizing tires according to Intended speed (low, medium, high); by adding L, M, or H to the numerical rating. In this case, a typical rating number might be M-080-22-7573. The temperature-load endurance ratings would then be based on something like 70, 100, and 120 miles per hour, for low, medium, and high speed tires.

REFERENCES

1. Heitzman, E. J., Unpublished notes on antiskid braking devices (1957).

2. Grime, G., and Stiles, C. G., "The skidresisting properties of roads and tires," Papers on skidding and braking, The Institution of Mechanical Engineers, Automobile Division (1954-55, No. 1).

3. Sawyer, Richard K., and Kolnick, Joseph H., "Tire-to-surface friction coefficient measurements with a C-123 airplane on various runway surfaces," NASA (Rept. No. 20) (June 1959).

4. Chase, T. P., "Passenger car brake performance," SAE Transactions (vol. 13, No. 1) (January 1949).

5. Heitzman, E. J., Flight Mechanics Seminar on Automobile Dynamics, Department of Aerospace and Mechanical Sciences. Princeton University (November 1964).

6. Horne, Walter B., and Dreher, Robert C., "Phenomena of pneumatic tire hydroplaning." NASA (TN D-2056) (November 1963).

7. Horne, W. B., and Leland, T. J. W., "Influence of tire tread pattern and runway surface condition on braking friction and rolling resistance of a modern aircraft tire," NASA (TN D-1376) (1962).

8. Steckel, S. S., and Westberg, J. V., "Full scale evaluation of an airjet system as a means to eliminate the harmful effects of wet runways," Douglas Aircraft Co. (LB32662) (Oct. 19, 1965).

EDWARD J. HEITZMAN, TECHNICAL DIRECTOR

RESEARCH

Academic background

Mr. Heitzman received the M.E. degree from Stevens Institute of Technology in 1956. He has done graduate work in mathematics, engineering mechanics, and servomechanisms at Wayne State University, Detroit; aerodynamics at University of Detroit; airplane dynamics, automatic controls, and instrumentation dynamics at Princeton University.

Professional experience

From 1956 to 1959 Mr. Heitzman was a research engineer at the General Motors research staff, where he worked on analysis of tire characteristics. automobile handling studies, hydropneumatic suspensions, brake design, and structures. In 1958, as a consultant to General Motors Styling Division, he helped set up the first of a continuing series of wind-tunnel tests. After suggesting a novel Automobile structure which promised to reduce the amplitude of resonant body vibrations, he transferred to General Motors Styling Division in 1959 to direct its development. From 1959 to 1964 he directed design of structures and suspensions on researchstage future production cars, and carried out research in aerodynamics, vehicle handling, and body-chassis structures.

In 1964 Mr. Heitzman went to the department of aerospace and mechanical sciences at Princeton University to study adaptation of aircraft dynamics technology to automobile problems. He will join the research staff of the university in August 1966 as project engineer on a research program in automobile safety. The goal of that program is measurement of dynamic responses of human drivers In mathematical model form; theoretical study of stability of the car-driver system with average (50 percentile) and poor (1 percentile) drivers; and experimental verification using driver-analog autopilots in a variable stability car. Mr. Heitzman has designed the variable stability research vehicle and data acquisition system on which the project is based. ROBERT

CUMBERFORD,

TECHNICAL

DESIGN

Academic background

DIRECTOR

Mr. Cumberford studied industrial design at the Art Center School. Los Angeles, and the humanities at UCLA.

Professional experience

From 1954 to 1957 Mr. Cumberford was a designer in General Motors Styling Division, where he was assigned to special studio 5 and the Chevrolet studio before being made head of special studio X. His work at GM. included formulation of the company's standard layout for instruments and controls which was adopted in 1955.

From 1957 to 1963, he was a freelance writer, living in San Francisco, New York and Mexico City. He has published more than 200 magazine articles in several countries, gaining a reputation as a critic of automobile design.

In 1959, he was design assistant to Mr. Albrecht Goertz, whose industrial design practice is worldwide in scope.