Tire Construction Research Articles

Dynamic Indoor Tire Testing and Fourier Transform Analysis

Abstract Laboratory tire tests for dynamic spring rate and damping, steady state forces and moments, rolling radius, and cornering force transient measurements are described. Data are shown for bias, belted bias, and radial constructions in a range of automobile tire sizes. The significant differences in the results are noted on all tests for the three tire constructions.

Tire Testing for Rolling Resistance and Fuel Economy

Abstract The rolling resistance of tires and the fundamental factors influencing rolling resistance during laboratory and road testing are discussed. Test methodologies for vehicle fuel consumption, vehicle coast-down, rolling resistance trailer measurements, and laboratory testing are described. This paper is confined to passenger tire characteristics and deals primarily with test techniques, although some observations are made regarding tire construction, the effect of environment, comparison of test methods, test parameter effects, and the interrelationships between various test modes.

Energy Losses in Tires

Abstract Tire rotation is impeded by a drag force of 10 to 20 lb per 1000-lb load in normal vehicle operation. The principal cause is hysteresis, which is a function of the viscoelastic properties of the rubber and cord components, the way these materials are used in the tire, and the way the tire is operated. The influence of material properties has been well documented, and many laboratory tests have been developed for their measurement. Of even greater importance to energy losses, however, is tire construction. This subject is developed by consideration of the forces and moments involved in tire operation and of the mechanisms of energy loss. The importance of service conditions is emphasized by a discussion of the factors influencing rolling resistance. Tire rolling losses can be an important fraction of the total power consumption in low-powered vehicles. Future trends in tire engineering, and their effects on rolling resistance, are discussed.

Heat Generation in Tires Due to the Viscoelastic Properties of Elastomeric Components

Abstract The relationship between the heat generation as experienced in the tire shoulder and the viscoelastic properties of the tire elastomeric components has been formulated. The analysis was facilitated by adopting the technique of multiple regression where the significance of each response equation was statistically evaluated. The physical intepretation and consequences of such response equations have been extensively discussed, whereas literature on the subject is incomplete. Effects of tire construction and size on the heat generation in the shoulder region was carried out by analyzing the results of tires that had reached a state of thermal equilibrium on an indoor tire-dynamometer. The tires used in the analysis were cross-ply and radial-ply passenger tires and cross-ply truck tires. Within the limits of such an analysis, the heat generation experienced in the tire shoulder was predominantly due to the condition classified as that of constant stress amplitude.

Variations in Tire Hysteretic Losses Due to Tire Design

Abstract The technique of analyzing energy losses of tires that have reached a state of thermal equilibrium has been applied to cross-ply and radial-ply passenger car tires and cross-ply truck tires. The derived formulations relating the tire energy losses to the viscoelastic properties of the tire components show the dependence of these losses on tire size and construction. The analysis was carried out by systematically varying tire tread compounds and operating parameters. This investigation of the energy losses experienced by tires operating in a state of thermal equilibrium, has enabled the losses due to the various stress-strain deformations to be characterized. In particular, the losses due to the strain deformation have been correlated with two mechanisms, which are outlined. The results described enable a better understanding of the mechanisms responsible for tire energy losses and allow the tire losses to be predicted at the design stage.

Mechanics of the Pneumatic Tire. Part II. The Laminar Model under Inflation and in Rotation

Abstract Difficulties in the study of the tire are presented by the materials used in tire construction, specifically the problem of achieving a convenient representation of the elastic characteristics of the rubberized fabric. Notable progress has been made in the formulation of the theory of combined orthotropic laminae which includes the contribution of the rubber compound and, more importantly, the effects of combining layers or plies having different characteristics. The laminar model of the tire is of particular interest for the study of the radial tire in which the effect of the carcass-belt combination is very important. This study first considers the tire under inflation alone and gives illustrative examples of applications to several types of tires. The net model for the bias ply tire is discussed as a special case of the theory. The study is then extended to consideration of the effects of centrifugal force in rotation in addition to inflation pressure.

Fiber properties required for tires

AbstractContrary to what the appearances would suggest, a pneumatic tire is basically an engineered textile object rather than a rubber one. The functional characteristics and performance of tires are chiefly determined by the properties of the textile fibers and by the way in which they are disposed in the tire structure. The specific roles of some of these properties (e.g., modulus, tensile strength, fatigue resistance, hysteresis) will be related to tire performance. Different tire constructions require a different balance of textile properties for optimum performance. Belted tires, and especially radial ply tires, present a different set of requirements for optimum textile fiber performance in tires. The nature of the differences are discussed.

A combined approach to the optimisation of tyre and pavement interaction

The development of pavement surfacing technology with regard to skid resistance, and advances in the understanding of tyre to pavement interaction are reviewed. The influence of these advances on the construction of pavement surfaces and design of tyres in Great Britain is discussed. In order to control some of the variables present in roadhold measurements and to develop and test pavement surfacings and tread compounds under laboratory conditions a Variable Speed Internal Drum Machine has been built and is described. Pavement texture studies made with the aid of the scanning electron microscope have shown how pavement surfaces polish due to traffic action and roughen due to climatic changes. These changes are related to skid resistance measurements. The various types of tread compound abrasion are reviewed and the parameters influencing their occurrence listed. Recent work on a special form of abrasion termed “reversion” discusses the conditions governing its formation. The concept of the three zone contact path is discussed with regard to recent developments in tyre construction, tread patterns and pavement surfaces. Special reference is made to the development of pavements using artificial aggregates and use of natural aggregates of the gritstone group. The introduction of such surfaces will have important effects on tread abrasion rates. The work described in this paper shows the need to combine the knowledge of pavement and tyre technologists in order to design the pavement and tyre as a unit and hence to optimise the general tyre and pavement performance.

Aircraft tyres—an analysis of performance and development criteria for the 70s

In this paper the many aspects of tyre performance criteria are discussed, as they have developed over the last decade. The corresponding tyre developments that have been effected to date are set out in considerable detail, together with the forward developments which are currently engaging the skills of modern tyre designers.For the most part the paper deals with the present standard aircraft tyre, of conventional or cross-ply construction (Fig. 1), but the future role of the radial ply tyre (Fig. 2) is treated in some detail.

Performance of Tread Compounds in Various Tire Constructions

Abstract There are now three major types of construction used in passenger car tires—cross-ply (or bias), belted cross-ply, and radial. The same rubber compounds and tread designs may not always provide optimum performance in these but it was considered of interest and importance to compare the relative performance of several typical tread compounds on each type of tire. Four tread compounds were applied as retreads to four tires of each type. These were road tested over a highway route which included some rapid cornering. Two polymer systems were employed: 1. a low vinyl, 85/15 butadiene/styrene, oil-extended, solution copolymer and 2. a 40/60 blend of high-cis polybutadiene/SBR 1712. These were reinforced with N330 (HAF) and N339 type carbon blacks. Some other tire tests were also available for supporting evidence. The solution copolymer gave 8 to 12% better resistance to abrasion than the polybutadiene/SBR blend. The N339 carbon black was 10 to 15% better in wear resistance than N330 black and the best combination was 23% improved over the poorest. These relationships were affected very little by the type of tire construction and indicate that treadwear data on compounds in one type of tire may be useful to predict performance in another. Results also indicate that treads of equal composition will provide a mileage ratio of approximately 1 to 1.5 to 2 or 2.5 on cross-ply, belted cross-ply, and radial tires, respectively.

Rubber Strain Measurements in Bias, Belted-Bias and Radial Ply Tires

The two-dimensional state of strain on the inner and outer surfaces of automobile tires operating under straight ahead rolling conditions was experimentally determined for bias (cross-ply), belted-bias and radial ply tires of comparable size. The strain transducer employed was fabricated by embedding a column of liquid mercury in a small billet of silicone rubber. The principle of operation of this gage is similar to that of the conventional bonded electric resistance strain gage used with metals - i.e., a change in resistance of the mercury capillary is linearly related to the strain in the direction of the column. These gages were mounted in three directions at locations from the bead to the crown and the measured strains were used to calculate the maximum tensile, compressive and shearing strains. The de formation characteristics of the different tire constructions were compared at various wheel loads and inflation pressures. The experimental results in dicate that membrane strains predominate in the inflated but otherwise un loaded tire, while bending strains predominate in the region of the contact zone of the rolling tire. The magnitude of the maximum shearing strain is, in general, greater than or equal to the maximum tensile strain. The direction of the maximum shearing strain in a plane tangent to the rubber surface, in general, coincides with the cord direction in the ply closest to the tire surface.

The Influence of Geometric and Cord-Load Design Parameters on the Profile Shape and Cord Tensions in Inflated Pneumatic Tires

A mathematical model for the bias-ply pneumatic tire is presented. Based on the linear-membrane theory of thin shells of revolution, the present model exhibits greater generality in development and flexibility in use than previous models. As presented here, the model has the capability of defining meridian profiles as a function of geometric and cord-load parameters designated at any point on the tire carcass. The result is a model capable of effecting parametric studies for the effects of tire design and construction constraints on carcass shape and cord load.

General Method for Approximating the Tire Contour Integral for Arbitrary Cord Path

Abstract It has been shown that the tire contour integral can only be evaluated exactly in terms of elementary functions and elliptic integrals in special cases. Approximate numerical methods, with computer programming, have been used heretofore to calculate contours which result from conventional, bias-angle tire construction, by assuming the cord path: ρ/cos α=ρ0/cos α0. In calculating the contours, for deflected tires having such a cord path, a new approximate method of evaluating the contour integral was described which expressed the contours in terms of elliptic integrals.

Discussion

Abstract Mr. W. B. Horne (NASA, Hampton, Virginia)—Results in the two papers are in agreement with NASA research results. The papers treated the subjects of tread material, tire construction, road surface texture, and tread design very thoroughly. But one essential ingredient to the problem has been left out of the paper discussions, and that is, the effect of water depth. The importance of the water depth effect, and the need to inform both public and government authorities about the importance of removing worn tires from automobiles for the safety of all, is discussed and illustrated very fully by Leland. An example of what happens when the water depth is 0.4 in. is shown in Figure 1. It can be seen that the water penetrates the tire imprint much more rapidly than in shallow water. The effect of road surface texture on braking friction coefficient is illustrated by the data shown in Figure 2. A smooth tread aircraft tire was successfully braked on five different road surfaces ranging in texture from a large aggregate asphalt surface to wet ice. These surfaces are classified as damp in wetness. The surfaces at the time of testing were wet to the touch but did not have any puddles or standing water. Under this condition, damp smooth concrete (smooth as a table top) gave friction values as low as wet ice. This drastic friction loss decreased as the road surface texture increased. It will be noted that the smooth aggregate asphalt data did not fall off in speed as was shown by Maycock in his paper in Figure 15. In Figure 3 the water depth on the smooth concrete and large aggregate asphalt surface was increased from a damp condition to a flooded condition (0.1–0.2 in.). The character of the friction changes of these surfaces due to change in water depth is remarkable. For example, the smooth concrete increased slightly in value. This is an apparent increase, however, because the deeper water produces a fluid drag term which adds to the tire-surface braking force and gives a higher friction coefficient. This is an academic point, however, since the smooth concrete surface is producing viscous hydroplaning even at low speeds. On the other hand, the asphalt surface which alleviated the viscous hydroplaning effect under damp conditions does not prevent dynamic hydroplaning from occurring to the tire when this surface is flooded to a depth of 0.1 to 0.2 in. To summarize, any surface must be evaluated under a range of water depths before its wet friction qualities can be properly evaluated. Smooth tread tires or badly worn patterned tires have demonstrated poor friction capabilities on most wet or flooded surfaces. For this reason, both aircraft and automobile tires should be removed and replaced before wear produces a smooth tread condition.

Paper 6: Tyre Forces as Functions of Cornering and Braking Slip on Wet Road Surfaces

The pure braking and cornering forces of a given tyre on a given wet surface at a given speed are functions of braking slip and slip angle respectively. These functional relationships are of great importance in connection with the handling and stability of vehicles and the behaviour of brakes and antilocking devices. When cornering and braking occur simultaneously the forces interact and the functional relationships are modified, with consequent effects on vehicle characteristics. The empirical data available at the Laboratory on these relationships, both for pure forces and for forces in combination, are presented. The known effects of such factors as speed, road surface texture, tread pattern, tread resilience, and tyre construction are reported, but since the work was carried out at various times and for various purposes the coverage is incomplete and uneven. The test vehicle, test procedure and the methods of measuring and evaluating the data are briefly described. Some data have been analysed statistically to discover the dependence of the various frictional coefficients on factors such as those mentioned above. It is believed that greater use should be made of these statistical techniques in future work. Raw data can also be converted into such practical quantities as braking distances, wheel locking times, etc., by computing theoretically the behaviour of model braking systems. An example of such a study is given. The principal features of the mutual effect of braking and cornering forces may be summarized as follows: (a) If curves of sideway force against slip angle are plotted for constant values of braking force, there is little change of initial slope, but the maximum sideway force and the slip angle at which it occurs are reduced. If, however, the curves are plotted for constant braking slip, then the initial slope is decreased and the slip angle for maximum sideway force is increased; at this same angle the sideway force at zero braking slip will only be slightly greater. (b) The presence of a fixed amount of angular slip reduces the initial slope of the curve of braking force against braking slip, reduces the maximum value of the force, and increases the slip at which it is attained. (c) In a few cases examined, if resultant force is plotted against resultant slip for a given speed, tyre, and surface, there is a tendency for the points to lie in a fairly definite band having a form similar to that of the braking force–braking slip curve.

Construction and Behaviour Characteristics of Tyres

Development of automobile tyres over the past few years has led to certain improved performance characteristics and also to a wider choice of tyre behaviour patterns than has earlier been the case. To obtain optimum required performance characteristics for a particular vehicle design, attention must be paid both to individual tyre parameters and their interaction with particular features relating to the vehicle. Examples are given. The impact of new materials for making tyres and of constructional variations in the tyres is discussed in relation to improved tyre performance characteristics, including comfort, road adhesion, ease of control, high-speed running, tread pattern life, noise and tyre power consumption. Testing techniques which have assisted in assessment of some of these items are discussed, with illustrative results. The relative effects of mechanical and tyre variables are summarized. Reference is made to future trends in requirements of automobile tyre behaviour and possible consequent changes in tyre construction and form.

The Latexing and Hot-Stretching of Tire-Cord Fabrics With Special Emphasis on Nylon

Abstract It is estimated that 1.67 billions of tires have been made in the United States since the advent of the motorcar and truck. There have been many types of tire constructions, tread designs, and manufacturing methods; however, now practically all tires have the same general construction design. Processing of both the fabric body and the rubber stocks has improved greatly. These improvements have resulted in a better tire with longer mileage capacity and much better service life. This paper deals specifically with cord fabrics as used in passenger and truck tires and summarizes the general processing requirements and techniques as carried on in the United States. Emphasis is placed on nylon fabric, principally because of the present tendencies of the American manufacturers to accept nylon-cord fabric as being superior to cotton and rayon for many important tire-cord requirements.

Retraction and Stress Propagation in Natural and Synthetic Gum and Tread Stocks

Abstract Natural and synthetic rubbers (elastomers) are characterized by their long-range reversible elasticity. More particularly, the existence of a retractive force distinguishes rubbers from materials like beeswax, which may be extended but do not snap back. Whereas all rubbers show a snapback, the good rubbers show a fast snapback. Thus the speed of snapback is an outstanding index to the quality of the rubber. For instance, both Hevea and Butyl show snapback, but Butyl snaps back much more slowly than Hevea. This is the reason for the poor rebound in Butyl. Incidentally, the speed of snapback may be, and actually is, used as a simple “hand test” for progress of cure. One bends a cured sheet and observes how fast it straightens out again. In this example the speed of recovery after bending is observed. The speed of snapback may be studied, of course, for any deformation : bending, torsion, shear, compression, extension, etc. Since stress-strain data are used so extensively in rubber technology, snapback after extension was studied first. Snapback will be used in this restricted sense in the following text. Besides characterizing the quality of a polymer, the speed of snapback is of great direct importance for tire construction. Sluggish snapback may lead to increased flexing, i.e., increased heat generation. In addition, slow snapback means less grip of the tire on the road, assuming equal wetting conditions.