A straight-line braking test for truck tires.The purpose of the work reviewed in this article is to establish a standardized test A standardized test is a test administered and scored in a standard manner. The tests are designed in such a way that the "questions, conditions for administering, scoring procedures, and interpretations are consistent" [1] procedure for producing straight-line braking properties of heavy duty truck tires for use in vehicle dynamics Vehicle dynamics refers to the dynamics of vehicles, here assumed to be ground vehicles. For two-wheeled vehicles see Bicycle and motorcycle dynamics. For the dynamics of air vehicles see Aerodynamics. simulations. (Heavy duty trucks are taken to include all commercial over-the-road trucks and buses). This work is part of a total project whose objective is to produce broadly accepted test procedures for three important tire operating regimes: free-rolling cornering, straight-line braking, and combined cornering and braking (ref. 1). The test procedures which are developed are to be expressed as SAE sae abbr (BRIT) (= stamped addressed envelope) → sobre con las propias señas de uno y con sello Recommended Practices (J-Documents). This study was conducted as a SAE Cooperative Research project under the supervision of the Truck Tire Characteristics Task Force. The task force is composed of a group of engineers from the truck manufacturers, tire manufacturers, government, and testing organizations who are all interested in improving the ability of the engineering community to perform analytical design in support of good handling. Many members of this group helped with the work reported. This project began with the synthesis of test procedures for free-rolling cornering, straight-line braking and combined cornering and braking tests. Then experimental evaluations for each procedure were designed. From these, the Statement of Work (SOW sow a female pig that has had a litter. sow mouth the maxilla is foreshortened and the lower jaw protrudes beyond it. sow stall ) (ref. 1) was assembled. Although development of three procedures is intended, this article deals with only the one for the straight-line braking test. The task force chose to examine and compare the capabilities of the two public-domain pieces of equipment able to test heavy duty truck tires. One is at Calspan, and the other is at UMTRI UMTRI University of Michigan Transportation Research Institute . All testing at Calspan was done using the large flat-surface Tire Research Facility (TIRF TIRF Traffic Injury Research Foundation TIRF Total Internal Reflection Fluorescent (microscopy) ) machine. The TIRF machine has a single measuring station centered over a stainless steel stainless steel: see steel. stainless steel Any of a family of alloy steels usually containing 10–30% chromium. The presence of chromium, together with low carbon content, gives remarkable resistance to corrosion and heat. belt. The measuring station is equipped with a five-component load cell for transducing tire forces and moments. The belt is coated with an emery cloth Noun 1. emery cloth - cloth covered with powdered emery abradant, abrasive, abrasive material - a substance that abrades or wears down or sand paper to simulate pavement micro-texture. The steel belt is supported by an air bearing in the tire contact region and rotates on two 67 inch steel drums steel drum Tuned gong made from the end, and part of the wall, of an oil barrel. The barrel's end surface is hammered into a concave shape, and several areas are outlined by chiseled grooves. . All testing is conducted under computer control. The machine is capable of performing free-rolling cornering, straight-line braking or combined cornering and braking tests on truck tires. The machine can also perform wet testing and has numerous other capabilities useful in testing passenger and light truck tires. All testing at UMTRI was done on the Mobile Truck Tire Traction Dynamometer dynamometer /dy·na·mom·e·ter/ (di?nah-mom´e-ter) an instrument for measuring the force of muscular contraction. dy·na·mom·e·ter n. An instrument for measuring the degree of muscular power. (herein, the Mobile Tire Tester, or the Mobile). The Mobile Tire Tester consists of a long-wheelbase, three axle axle Pin or shaft on or with which wheels revolve; with fixed wheels, one of the basic simple machines for amplifying force. Combined with the wheel, in its earliest form it was probably used for raising weights or water buckets from wells. highway tractor towing a single axle semitrailer sem·i·trail·er n. A trailer having a set or several sets of wheels at the rear only, with the forward portion being supported by the truck tractor or towing vehicle. . The device has two test stations. A single test tire may be mounted on the centerline cen·ter·line n. 1. A line that bisects something into equal parts. 2. A painted line running along the center of a road or highway that divides it into two sections for traffic moving in opposite directions, or, in the case of test station located at the mid wheelbase wheel·base n. The distance from the center of the front wheel to that of the rear wheel in a motor vehicle, usually expressed in inches. wheelbase Noun of the trailer. This test station is for brake force Brake force is a measure of braking power of a vehicle. In the case of railways, it is important that staff are aware of the brake force of a locomotive so sufficient brake power will be available on trains, particularly heavy freight trains. testing only and was not used in this project. The second test station is based on a special axle mounted at mid wheelbase on the tractor. Free-rolling cornering, straight-line braking or combined cornering and braking testing may be done at this test station. The wheels on the test axle run outboard Not built in. Outboard devices are external to the main unit. Contrast with inboard. See offboard. of the nominal eight foot vehicle width. The spindle spindle: see spinning. A rotating shaft in a disk drive. In a fixed disk, the platters are attached to the spindle. In a removable disk, the spindle remains in the drive. Laptops use spindle designations to indicate the number of built-in drives. on the right side of the axle is equipped with a six-component load cell for transducing tire forces and moments. The spindle on the left is not transduced. The left tire serves only as a counteracting tire so that slip angles may be introduced by toeing the two tires toward each other while minimizing disturbance to the Mobile's path. Each wheel position is equipped with a very high capacity disk brake which allows aggressive braking programs with little concern for overheating Overheating An economy that is growing very quickly, with the risk of high inflation. . The task force specified that all work be done in customary (English) units since the majority of the target group is still working in these units and use the SAE J670e vehicle dynamics definitions (ref. 2). This article follows the task force's direction, but does use SI units (Système International d'Unites) A system of standard units of measurement finalized at the 14th General Conference on Weights and Measures in 1971. It is based on seven units of measure, including three from the MKS system (meter-kilogram-second), the ampere for as subordinate units. The body of this article begins with a brief discussion of the full test procedure developed in the project and applied by Calspan and UMTRI. Following the presentation of the procedure, the actual tire measurement results obtained by UMTRI and Calspan, and analyzed by Smithers Smithers is a surname, and may refer to: People People with the surname Smithers
Test procedure The test procedure has not yet been formally arranged into the format used in a recommended practice. Instead this section gathers together those elements which will be formally assembled by a specially appointed task force. Cautions There are two main cautions: * Tire force and moment properties change significantly over time as tires age (ref. 3). Therefore, test tires must be stored under equivalent or well understood conditions to prevent invalid judgments. Either vehicle models or tests using tires of very different ages or tires stored at very different temperatures cannot be taken as representing a true comparison of the tire specifications being studied. * Ambient temperature Outside temperature at any given altitude, preferably expressed in degrees centigrade. during testing influences tire force and moment properties. Strict control is desirable. However, practical productivity problems in over-the-road force and moment testing require establishment of an ambient temperature range. A temperature range of 60[degrees]F to 80p[degrees]F (16[degrees]C to 27[degrees]C) was chosen for this work. This limit was chosen on the basis of lateral force, [F.sub.y] behavior which is documented in the literature (ref. 4). This was a reasonable approach given the fact that we chose to apply the same limit to all three types of tests. The expected temperature associated [F.sub.y] error is less than two percent. Inflation pressure Tire force and moment properties are strong functions of inflation pressure. Therefore, we chose an inflation pressure representative of actual tire service for the tire specification under test rather than an arbitrary pressure. This pressure was determined through a small pretest pre·test n. 1. a. A preliminary test administered to determine a student's baseline knowledge or preparedness for an educational experience or course of study. b. A test taken for practice. 2. based on experience with heavy duty tires. The procedure follows: * Mount the experimental tire on the test rim specified by the appropriate tire and rim standards organization A standards organization, also sometimes referred to as a standards body, a standards development organization or SDO (depending on what is being referenced), is any entity whose primary activities are developing, coordinating, promulgating, revising, amending, , for example, the Tire and Rim Association. * Inflate inflate - deflate the tire to the target cold inflation pressure Cold inflation pressure is the inflation pressure of tires before the car is driven and the tires warmed up. Recommended cold inflation pressure is displayed on the owner's manual, the placard (or sticker) attached to the vehicle door edge, door post, glove box door or fuel door. specified by the test requester and cap the valve. * Run the tire for one hour at the following conditions: inclination angle See: pitch angle. , [gamma] = 0 degrees; slip angle, [alpha] = 0 degrees; normal force, [F.sub.z] = -(rated load for the target cold inflation); and specified test speed (S) for one hour. * At the end of one hour stop the tire and measure the inflation pressure (P). P is the inflation pressure that will be used during tire conditioning and test. Pre-test conditioning The force and moment properties of tires are dependent on tire operating temperature, tire wear state, and the exercise state of the tire materials, as well as the intrinsic properties of the tire as manufactured. The pre-test conditioning (which will be the same for all three Recommended Practices) was designed to assure thermal equilibration equilibration /equi·li·bra·tion/ (e-kwil?i-bra´shun) the achievement of a balance between opposing elements or forces. occlusal equilibration of the test tire and produce a modest, consistent exercise of a new tire prior to actual testing. The purpose of the pre-test is to simulate the condition a new tire is apt to exhibit after a few hours of highway usage. The pre-test conditioning procedure is as follows: * Mount the experimental tire on the test rim specified by the appropriate tire and rim standards organization. * Inflate the tire to the test inflation pressure (P) using a pressure regulator A Pressure regulator is a valve that automatically cuts off the flow of a liquid or gas at a certain pressure, usually for the purpose of preventing damage to plumbing. Pressure regulators are often used at the main entrance of water to a building. . The pressure regulator stays in effect throughout pre-test conditioning and the braking test itself. * Load the tire at [F.sub.z] = -(rated load for the target cold inflation). * Operate the test tire in accordance with the instructions table 1. Speed (S) is at the discretion of the tester, but should be maintained throughout the entire test sequence. Table 1 - pre-test conditioning steps Step Distance [alpha], degrees #1 S x 1 hr. 0.00 #2 0.5 mi. (0.8 km) 1.00 #3 0.5 mi. (0.8 km) -1.00 * Maintain inclination angle, [gamma] = 0.0 degrees. Warm-up in case of a broken test If a test must be stopped because of an equipment problem or other limitation, not due to a tire problem, the tire shall be warmed up at S for one hour at [alpha] = [gamma] = 0.0 with inflation pressure and normal force as specified in the pre-test conditioning before testing is resumed. The test Immediately following pre-test conditioning, without stopping, measure the tire straight-line braking response according to according to prep. 1. As stated or indicated by; on the authority of: according to historians. 2. In keeping with: according to instructions. 3. the test matrix specification in table 2. (See the next section for a full description of the data to be acquired). The sequence is: set the first [F.sub.z], perform the braking ramp release, set the second [F.sub.z], perform the braking ramp, release, and so forth until completion. The braking ramp is from a slip ratio, SR, of 0.0 to an SR of -0.8 at a rate of -0.8/sec. Data acquisition and reporting During each test step, the following data are to be acquired at least every 0.01 increment To add a number to another number. Incrementing a counter means adding 1 to its current value. of slip ratio: [F.sub.x] (longitudinal force), [F.sub.y], [F.sub.z], [M.sub.x] (overturning moment), [M.sub.z] (aligning moment), [R.sub.1] (loaded radius), [alpha], [gamma], and [omega] (tire angular velocity). These data are to be reported to be spoken of; to be mentioned, whether favorably or unfavorably. See also: Report at every 0.01 increment of slip ratio: [F.sub.x], [F.sub.y], [F.sub.z], [M.sub.x], [M.sub.z], [R.sub.1], [alpha] y and SR. The data reports are to be as ASCII files A file that contains data made up of ASCII characters. It is essentially raw text just like the words you are reading now. Each byte in the file contains one character that conforms to the standard ASCII code (see ASCII chart). using a defined format (ref. 5) Control tire procedures Control tires were not employed in the test programs reported herein. However, during the course of this testing, two types of errors were seen which might have been caught by the use of control tires: friction degradation of artificial surfaces due to changes in the roadway surface at Calspan with use, and gain errors in slip angle. Friction change also occurs over time on normal road surfaces. Suggested protocols for using control tires to deal with both types of errors have been developed and are reported elsewhere (refs. 6 and 7). Limitations of the test equipment Both the Calspan and UMTRI test machines have mechanical limitations. Those which could impede combined straight-line braking tests performed according to the test procedure in this report are listed below. Please note that other limitations may become crucial in tests done according to different test procedures. Those other limitations which may affect free-rolling cornering or combined cornering and braking tests are considered elsewhere (refs. 7 and 8). Calspan These are the limitations of the Calspan machine as perceived at the time the work being reported was done: * Inflation pressure: None so long as values are consistent with the requirements of the appropriate tire and rim standards organization. * Initial test speed: None from normal highway speeds downward. Speeds of up to 200 mph (320 km/hr) are possible on the TIRF machine. * Speed control: If [F.sub.x] is very large, the roadway will slow. * Tire diameter: 47 inches (1,195 mm) maximum. * Tread width: 24 inches (610 mm) maximum. * Inclination angle: None which affect this procedure. * Slip angle: None which affect this procedure. * Forces: [F.sub.x], -7,500 lb. (-33,400 N) < [F.sub.x] < 7,500 lb. (33,400 N). This limit is associated with the belt drive and the relationship between the kinetic energy kinetic energy: see energy. kinetic energy Form of energy that an object has by reason of its motion. The kind of motion may be translation (motion along a path from one place to another), rotation about an axis, vibration, or any combination of in the system, the capacity of the drive, and the rate at which the braking event drains energy from the system. The quoted limit is for the test discussed in this article. The force measuring balance has a capacity of [+ or -] 9,000 lb. ([+ or -] 40,000 N); [F.sub.y], none which affect this procedure; [F.sub.z], -12,000 lb. (-53,500 N) < [F.sub.z] < 0. This is an increase from the -10,000 lb. (14,500N) limit in use when the tests reported in this article were being performed. This limits testable normal force. * Moments: [M.sub.x], none affecting this procedure; [M.sub.z], none affecting this procedure. UMTRI Since the UMTRI Mobile is an over-the-road device based on a truck chassis, it is affected by wind, tire pull forces, road camber cam·ber n. 1. a. A slightly arched surface, as of a road, a ship's deck, an airfoil, or a snow ski. b. The condition of having an arched surface. 2. and road roughness. In addition, slip angle and normal force are open loop control systems. Therefore, significant scatter scat·ter v. 1. To cause to separate and go in different directions. 2. To separate and go in different directions; disperse. 3. To deflect radiation or particles. n. is to be expected in the data. These are the limitations of the UMTRI machine as perceived at the time the work being reported was done. * Inflation pressure: None so long as values are consistent with the requirements of the appropriate tire and rim standards organization. * Initial test speed: S < 60 mph (96.5 km/hr) all conditions. May be further limited due to a combination of roadway geometry and engine power. Acceleration beyond 45 mph (72 km/hr) is time consuming. * Speed control: If [F.sub.x] is very large, the truck will slow rapidly. * Tire diameter: 54 inches (1,372 mm) maximum in standard configuration. The brake disc diameter limits testable tires to rolling radii ra·di·i n. A plural of radius. radii Noun a plural of radius greater than 19 inches (483 mm). * Tread width: 19 inches (483 mm) maximum in standard configuration. * Inclination angle: None which affect this procedure. * Slip angle: None which affect this procedure. * Forces: [F.sub.x], none affecting this procedure; [F.sub.y], none affecting this procedure; [F.sub.z], -24,000 lb. (-106,700 N) < [F.sub.z] < 0. Normal forces exceeding -15,000 lb. (-66,700N) require special ballast bal·last n. 1. Heavy material that is placed in the hold of a ship or the gondola of a balloon to enhance stability. 2. a. Coarse gravel or crushed rock laid to form a bed for roads or railroads. b. . * Moments: [M.sub.x], none affecting this procedure; [M.sub.z], none affecting this procedure. Discussion of tire measurement results The following sub-sections discuss the results of the measurement programs conducted by Calspan and UMTRI. The discussion first specifies the test tires, the test surfaces and test speed, then it addresses: the general functional form and repeatability of the measurements, a surface effect on indoor testing, the correlation of Calspan and UMTRI data, the number of samples required in test sets and the effect of the proposed test on a tire's properties which are expressed in terms of free-rolling cornering behavior. Test tires All test tires were 295/75R22.5 AMERI AMERI Association Marocaine d'Etudes et de Recherches Internationales (French) *S380 LP steer axle tires by General Tire The General Tire and Rubber Company is an American manufacturer of tires for motor vehicles. General Tire was founded in 1915 in Akron, Ohio by William F. O'Neil. In 1943 General Tire branched out from its core business by purchasing the Yankee Network and the radio stations . The five tire samples were composed of tires drawn at random from a 200 tire lot taken from a single day's production. Test surfaces The test surfaces used by Calspan and UMTRI are inherently different. This affects all the data and should be borne in mind at all times while examining the tire measurement results. Calspan must use an abrasive abrasive, material used to grind, smooth, cut, or polish another substance. Natural abrasives include sand, pumice, corundum, and ground quartz. Carborundum (silicon carbide) and alumina (aluminum oxide) are important synthetically produced abrasives. paper or an emery cloth as a friction surface since the TIRF roadway is a flexible steel belt which passes around the machine drums. In this project, it was intended that Calspan use 120 Grit See Grantor Retained Income Trust. 3Mite aluminum oxide aluminum oxide: see alumina. material as the test surface. However, some of the tests were run on gO and 120 Grit 3M Polycut, a longer lasting ceramic oxide material which was thought to offer long-time stability for the friction surface. UMTRI may use any conventional road surface on which they can run the Mobile Truck Tire Dynamometer. In this project UMTRI used a concrete oval track  It has been suggested that and be merged into this article or section. . A very significant surface effect showed in the UMTRI and
Calspan data as slip increased above magnitudes of 0.06 to 0.10. This
was not a problem in the free-rolling cornering data (ref. 7), but was
easily seen in the longitudinal force ([F.sub.x]) data from the straight
line braking tests (ref. 9) and in the combined cornering and braking
data (ref. 8). The pertinent part of these results will be discussed in
the section comparing the Calspan and UMTRI data.Test speed The test speed, S, used in this experiment was 45 mph (72 km/hr). This speed was chosen as a compromise between freeway operation and the capabilities of the UMTRI Mobile within the constraints of keeping a practical bound on testing time. Longitudinal force functional form and repeatability The functional form of the [F.sub.x] data is correct for both Calspan and UMTRI, but the precise curve shapes and levels differ as would be expected for braking data taken on surfaces with different friction characteristics. Figures I and 2 portray the average results for multi-tire tests at Calspan (ref. 10) and UMTRI (ref. 11). For example, the peak longitudinal force occurs at a much lower SR in the Calspan data than in the UMTRI data, the Calspan peak [F.sub.x] is lower in magnitude than the UMTRI peak, and the [F.sub.x] values differ as SR approaches -1.00. These differences are discussed in detail a bit later. The repeatability of the longitudinal force, [F.sub.x], measured at Calspan is generally good, but deteriorates as the normal force, [F.sub.z], approaches the TIRF Machine [F.sub.z] limit (table 3). The average standard deviation In statistics, the average amount a number varies from the average number in a series of numbers. (statistics) standard deviation - (SD) A measure of the range of values in a set of numbers. is [C.sub.c], = 132 lb.. (587 N). Repeatability of the UMTRI [F.sub.x] data is not as good as that shown by the Calspan data, but is constant over varying [F.sub.z]. The average U[sigma] = 278 lb. (1,237 N) is more than twice the average Co. The difference is probably due to the inability of the Mobile Truck Tire Dynamometer to control [F.sub.z] with the same precision as the Calspan machine. Table 3 - Calspan longitudinal force standard deviations as a function of normal force. [F.sub.z], Normal force [F.sub.z], Standard deviation lb. (N) lb. (n) -1,544 (-6,868) 70 (311) -3,088 (-13,736) 99 (440) -4,631 (-20,560) 100 (445) -6,175 (-27,468) 99 (440) -7,719 (-34,336) 99 (440) -9,263 (-41,204) 325 (1,446) Surface effect on indoor testing The data discussed in this section came about in part due to a testing error and a unilateral decision by the Calspan staff. A set of tires was tested at 110 psig (758 kPa) due to a misreading MISREADING, contracts. When a deed is read falsely to an illiterate or blind man, who is a party to it, such false reading amounts to a fraud, because the contract never had the assent of both parties. 5 Co. 19; 6 East, R. 309; Dane's Ab. c. 86, a, 3, Sec. 7; 2 John. R. 404; 12 John. R. of the inflation pressure determination section of the project's Statement of Work (ref. 1). The 110 psig (758 kPa) data were taken on 120 Grit 3Mite. The pressure error was discovered by the analysis contractor, and Calspan agreed to run another sample at 125 psig (862 kPa), the correct inflation pressure. Since data were now going to exist at two pressures, it was decided that Smithers should compare the data so that at least some pressure effect information would result. However, a unilateral decision on the part of Calspan resulted in a switch to a 120 Grit Polycut surface for the 125 psig (862 kPa) test series. Thus, an indoor surface comparison experiment was actually performed. It should be noted that this was not an ideal one-to-one comparison between the two surfaces as each surface had a different testing history prior to acquisition,of the data reported in this article. Based on the results discussed below there is clearly a need for a more extensive experiment exploring the effects of different test machine surface materials on measured tire performance. The data from the two test series are presented in figure 3 (ref. 10) which reveals some interesting points. To help make these points, three data ranges are indicated by the symbology sym·bol·o·gy n. 1. The study or interpretation of symbols or symbolism. 2. The use of symbols. symbology 1. the study and interpretation of symbols. Also called symbolism. in figure 3. For low slip ratios, -0.06 [less than or equal to] SR [less than or equal to] 0.00, the data represented by pluses overlaying o·ver·lay 1 tr.v. o·ver·laid , o·ver·lay·ing, o·ver·lays 1. To lay or spread over or on. 2. a. the circles, an excellent linear correlation exists (equation 1). (1) F.sub.X125] = -4.81 + 0 99701 [F.sub.x110] [R.sup.2] = 0.9932 As slip ratio increases to values near the peak, the data in the range of -0.10 [less than or equal to] SR [less than or equal to] 0.00 (represented by circles) begins to follow a curved path. Finally, examining all the data, the dots, the total picture is one of a highly nonlinear A system in which the output is not a uniform relationship to the input. nonlinear - (Scientific computation) A property of a system whose output is not proportional to its input. relation ship. This indicates two things. All sandpaper sandpaper, abrasive originally made by gluing grains of sand to heavy paper sheets. Today sandpaper is made primarily with quartz, aluminum oxide, or silicon carbide grains, and is graded according to the size of the grains. surfaces even of the same grit number are not equivalent. There is a definitive need to check sandpaper surface behavior over time because the surface will wear and may become contaminated contaminated, v 1. made radioactive by the addition of small quantities of radioactive material. 2. made contaminated by adding infective or radiographic materials. 3. an infective surface or object. . Results by Whitehurst and Neuhardt (ref. 12) show that outdoor surfaces also change over time. Unfortunately, we don't have the luxury of quickly renewing outdoor surfaces as can be done on indoor machines. Based on the results discussed in this section the control procedures mentioned earlier in this article have been proposed (refs. 6 and 7). They are being used in a follow-on program now beginning (ref.13). Comparison of Calspan and UMTRI data The Calspan and UMTRI [F.sub.x] results in figure 4 do not exhibit a general correlation. The resulting fishhook curves are probably again a result of the considerable difference in frictional properties of the two test surfaces. After seeing the results comparing 120 Grit 3Mite and 120 Grit Polycut, this is not surprising. Can we conclude anything about the probable correlation of the measuring systems themselves? Surprisingly, we can. Equation 1 showed that the 120 Grit 3Mite and 120 Grit Polycut results were highly correlated for small slip ratio. Therefore, it is logical to correlate Calspan [F.sub.x] results to UMTRI [F.sub.x] results in the range -0.06 < SR < 0.00. Figure 5 shows a linear correlation. As indicated in equation 2, the correlation is good, but the slope is not 1.00. (2) [CF.sub.x] = -178.14 + 1.2124 [UF.sub.x] [R.sup.2] = 0.9862 A correlation of lateral force measurements from the two machines performed on the same test surfaces used in this experiment yields an excellent linear correlation with a slope of 0.97 for slip angles between plus and minus 6[degrees], non-dimensional slips between plus and minus 0.10 (ref. 7). Together the two results imply that the measuring systems would yield significantly different [F.sub.x] (SR) results even when testing the same tire on identical surfaces. The number of tires needed in a sample The engineer always wants to know how many tires to include in test samples in order to have a valid expectation of being able to detect a given difference between tire specifications at a pre-defined level of confidence. For [F.sub.x] in straight-line braking, figure 6 provides guidance subject to the following cautions. (The other literature in this series (refs. 7 and 8) provides information like that in figure 6 for other forces, moments and test procedures). * The tires tested must be assumed to be as consistent across samples as those used in this test for the results presented in figure 6 to be generally correct. This is because the statistical conclusions are based on a composite machine and tire variance. Separating these two variances is not truly possible. * While the required sample sizes are considerably smaller with the Calspan machine than with the UMTRI Mobile Truck Tire Tester, the frictional realism of the test surface required to meet test objectives should be considered in choosing a test site. * A final analysis to confirm the level of confidence with which the observed differences indicate that the tire specifications are indeed the same or different should always be made by applying a method such as a paired, 2-tail Student's t-Test A t test is any statistical hypothesis test in which the test statistic has a Student's t distribution if the null hypothesis is true. History The t . Change in tire properties due to testing Since testing changes tire force and moment properties, a feature of the experimental design (ref. 1) was a check test of the free-rolling cornering properties at the end of each tire test. The thought was that if the check revealed little or no change in properties due to the test, then the test gives a valid representation of the tire's properties. A big change would indicate that the results were as much test artifacts artifacts see specimen artifacts. as tire properties. The check was done without stopping after the straight-line braking test. The check test was performed at rated load with [alpha] = [+ or -]1[degrees], [+ or -]4[degrees]. The results of the check test were compared to the results of the free-rolling cornering test (refs. 10 and 11). This was done for [F.sub.y] and [M.sub.z] from both machines and for [M.sub.x] for the Calspan machine. Figure 7 is an example comparison. In summary, the effects are minimal for practical purposes. These results would seem to warrant using a single test tire for both tests. If so, it is the authors' opinion that the braking test should come before the free-rolling cornering test, based on the wear exhibited during the tests. As an additional point of reference, the total wear during the straight-line braking test was always under 0.020 in. (0.5 mm) at any location with the tread surface exhibiting damage at the edges of sipes. Conclusions * The straight-line braking test proposed in this article is usable for its intended purpose. * The test does not appear to significantly change tire force and moment properties. * Calspan and UMTRI longitudinal force data do not correlate due to an important surface friction effect. * Calspan and UMTRI longitudinal force data should not be combined in a single vehicle dynamics model. * Control procedures to monitor surface evolution are a required part of the test. * Practical guidance for sample size decisions has been presented. [Figures 1 to 7 ILLUSTRATION OMITTED] References All reports by Smithers Scientific Services, Inc., which are listed below, are available through SAE Cooperative Research, SAE, Warrendale, PA. [1.] Statement of work, "Heavy truck tire characterization bid package, " SAE 5/20/92 as amended 10/6/92. [2.] J670e, "Vehicle dynamics terminology," SAE, Warrendale, PA, 1978. [3.] M.G. Pottinger and K.D. Marshall, "The effect of tire aging on force and moment properties of radial tires,"SAE 810066, SAE, Warrendale, PA, 1981. [4.] K.D. Marshall, R L. Phelps, M.G. Pottinger and W. Pelz, "The effect of tire break-in on force and moment properties,H SAE 770870, SAE, Warrendale, PA, 1977. [5.] M.G. Pottinger, "SOW 1.2.2 final report," Smithers Scientific Services, Inc., September 20, 1994. [6.] M.G. Pottinger, "SOW 1.2.1 final report," Smithers Scientific Services, Inc., August 7, 1994. [7.] M.G. Pottinger, W. Pelz, G.A. Tapia and C.B. Wullcler, "A free-rolling cornering test for heavy duty truck tires," presented at the Tire Society The Tire Society is a professional body, specifically an engineering society, whose mission is to increase and disseminate knowledge as it pertains to the science and technology of tires. It hosts a two-day Meeting and Conference every year. mtg., Akron, OH, 3/21-22/95, to be published in Tire Science and Technology Tire Science and Technology is a peer-reviewed, scholarly journal published by the Tire Society. The journal was founded in 1973, and published until 1977 by a committee of ASTM. . [8.] M.G. Pottinger, W. Pelz G.A. Tapia and C.B. Winkler Winkler may refer to:
[9.] M.G. Pottinger and W. Pelz, "Recommended test sample sizes (SOW 1.5) and the Calspan/UMTRI comparison (SOW 3.0) for SOW 1.2.2 data, " Smithers Scientific Services, Inc., September 9, 1994. [10.] M.G. Pottinger and W. Pelz, "Repeatability and pressure effect analysis for Calspan SOW 1.2.2 Data," Smithers Scientific Services, Inc., August 19, 1994. [11.] M.G. Pottinger, "Repeatability analysts for UMTRI SOW 1.2.2 Data," Smithers Scientific Services, Inc., September 8,1994 [12.] E.A. Whitehurst and J. B. Neuhardt, " Time-history performance of reference surfaces, " The Tire Pavement Interface, ASTM ASTM abbr. American Society for Testing and Materials STP STP or standard temperature and pressure, standard conditions for measurement of the properties of matter. The standard temperature is the freezing point of pure water, 0°C; or 273.15°K;. 929, M.G. Pottinger and T.J. Yager, Eds., American Society for Testing and Materials, Philadelphia, PA, 1986, pp. 61-71. [13.] Statement of Work for Phase I Part 2, Heavy Truck Tire Characterization Bid Package, SAE 4/21/95. Marion G. Pottinger, Smithers Scientific Services, George A. Tapia, Calspan Corp., Christopher B. Winkler, The University of Michigan and Wolfgang Pelz, The University of Akron Enrollment in fall 2006 was 23,539 students.[1] The school offers more than 200 undergraduate degrees [2] and 100 graduate degrees [3]. The University's best-known program is its College of Polymer Science and Polymer Engineering, which is located in a . |
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