Search Results

Accurate, real-world determination of tire force and moment properties is essential for computer modeling of vehicle handling. Characterizing these properties on surfaces ranging from dry pavement to snow to ice presents significant challenges. This paper reviews recent progress and results in this area for light truck tires using a test vehicle custom-designed for this purpose. It provides examples for free-rolling cornering, straight-line acceleration / braking and acceleration / braking in turns. The discussion then turns to the question of adapting the technology used to characterizing of tires for Class 8 vehicles.

The free-rolling cornering, straight-line braking, and pull force properties of a small sample of tire specifications is examined. This is done to examine potential differences between the specifications and the statistics of force and moment measurements. Two steer axle specifications, two drive axle specifications, and a trailer specification are considered, In addition, the evolution of properties for one drive axle specification is followed from new to naturally worn-out to retreaded. The summarized data is available from SAE Cooperative Research on electronic media.

The ability to accurately simulate vehicle dynamics behavior with a mathematical model is limited by the quality of the tire model. In fact, the tire is often the single most important component in determining correlation between a mathematical vehicle model and measured experimental results. Tire data for heavy trucks are more difficult and expensive to acquire than passenger car and light truck data, and, consequently, there has been little published experience testing or modeling these tires. This paper shows how the analysts can integrate heterogenous tire modeling methods into one coherent tire model suitable for the simulation of an over-the-road 18-wheel tractor-trailer configuration. The methods used in this paper are: Tire F&M modeling that represents the effect of tread wear, water depth, and speed, as well as combined longitudinal and lateral slip conditions.

The slip circle, COMBINATOR, model was developed to predict combined driving or braking and cornering performance of tires from straight-line torqued data and free-rolling cornering data only. In the original COMBINATOR paper, limited verification was presented. In the current paper, the model is shown to be broadly applicable to tires of all types. This is demonstrated through successful modeling of heavy-duty tires as large as 425/65R22.5 and by modeling of racing tires. The heavy duty tire models and summarized data are available from SAE Cooperative Research on electronic media.

A Paper-Tire is a virtual product defined as a set of force and moment equations that are entirely determined by well defined and widely recognized tire characteristics (such as cornering stiffness, peak location, and slide/peak ratio). The vehicle dynamicist may use the Paper-Tire concept to study the effects of tires with various hypothetical characteristics on vehicle behavior. If the dynamicist discovers a set of characteristics yielding a desired vehicle response, he could then ask tire manufacturers to attempt to develop a tire specification with the preferred characteristics. (There is, of course, no guarantee that tire manufacturers can develop a practical tire with the preferred characteristics.) The paper explains the general principles of the Paper-Tire concept with the help of the BNPS model (derived from the ‘Magic Formula’). A limited set of examples for tire cornering and braking performance are provided at a single load; further possible developments are indicated.

The traction effects of water depth, speed, tread wear, inflation, and load on typical 295/75R22.5 truck tires have been examined in a set of designed experiments conducted on a single pavement. The results have been typified in terms of regression models of aligning moment and lateral force at 4 degrees slip angle plus peak longitudinal force and longitudinal force at slide during braking. The effects of the principal parameters are catalogued. An approximate idea of the effect of the operational and tread wear state parameters on the ability to control vehicle motion is provided within the discussion.

The objective was derivation of a tire braking/cornering force model based on only a few standard tests, so that elaborate testing of all possible combinations of lateral and longitudinal forces could be avoided Such a model would be particularly useful for truck and bus tires because testing large tires is expensive and appropriate testing facilities are rare The required model can be derived from the concept of the slip circle (not a friction force circle) Using the slip circle concept, all tire forces at any cornering/braking combination can be predicted from the results of only two basic tests -- a free-rolling cornering test and straight-line braking test The slip circle concept has been incorporated into a subroutine called the COMBINATOR -- a piece of public domain software sponsored by SAE Cooperative Research This paper discusses the Slip Circle Model, introduces the COMBINATOR, and demonstrates effectiveness by comparison of modeling results and experimental data

The “Magic Formula” concept is an elegant, empirical method of fitting tire data for inclusion in vehicle dynamics models. Its behavior as a function of parameter values is explained in detail in this paper. This paper presents the BNPS model, a modification of the Magic Formula concept, which has been fully automated on a personal computer. This allows the ready reduction of data into practical Magic Formula type models without any investment of engineering time. BNPS fitting example results are presented.

Variability in the double lane change test, a common subjective handling test, is defined based on the specific test used by BFGoodrich in 1982. Eight test protocol elements apparently required to ensure one half rating paint discrimination at 90 percent or greater confidence are reported. Further study of four points is recommended prior to routine use of the protocol elements. All results derive from statistically designed blind tests of 12 specifications differing widely in tread compound properties. Ratings varied from four to seven.

The increase of rubber stiffness with age causes radial tire cornering stiffness to significantly increase during warehouse (shelf) aging. The increase in cornering properties is linear with the logarithm of time and dependent on storage temperature. Five different brands of radial tires studied age in a very similar manner, exhibiting the apparent effect of two different aging mechanisms. A limited experiment indicated an approximate balance of aging and break-in effects on radial tire cornering properties in normal service. The in-service results imply that neither force and moment tests nor vehicle handling tests should be preceded by break-in or scrub-in procedures if the desire is to predict in-service behavior.

The effect of test speed and surface curvature on tire force and moment properties has been investigated. Lateral force at low slip angles increases linearly 8 to 9 percent for a tenfold increase in test speed. The effect of test speed on tire force and moment properties produces only a modest change in predicted steady state vehicle handling, but a rather significant change in predicted transient vehicle handling. Surface curvature tends to reduce slip and camber generated lateral force and aligning torque, but the effect is extremely complex and no simple flat to curved surface transformation relationship exists.

The source of ply steer in radial carcass tires is out-of-plane bending to in-plane shear coupling in the tread band portion of the tire laminate. Laminate design controls the coupling and, therefore, controls ply steer. Design control is discussed and demonstrated through examples that eliminated ply steer. Aligning torque static phase is introduced. It conceptually simplifies vehicle pull problems. Ply steer in bias carcass tires is briefly discussed.

The effect on radial passenger tire performance of the four most common belt materials-fiberglass, Kevlar, rayon, and steel-is discussed in light of their contributions to tread band stiffness. The magnitude of the material effects on performance is compared to the magnitude of belt geometric design effects on performance. It is demonstrated that the belt material differences do have a significant effect on performance related directly to how the material differences affect tread band stiffness. It is also shown that other design effects can overwhelm differences due to material differences alone.