# ASTM F1112-06a (Reapproved 2010)

Designation: F1112 − 06a (Reapproved 2010)Standard Test Method forStatic Testing of Tubeless Pneumatic Tires for Rate of Lossof Inflation Pressure1This standard is issued under the fixed designation F1112; the number immediately following the designation indicates the year oforiginal adoption or, in the case of revision, the year of last revision. A number in parentheses indicates the year of last reapproval. Asuperscript epsilon (´) indicates an editorial change since the last revision or reapproval.1. Scope1.1 This test method covers the determination of the rate ofinflation pressure loss resulting from air diffusion through thestructures of tubeless tires under constant temperature condi-tions. The testing is done under static conditions, that is,nonrotating, nonloaded tires.1.2 The values stated in SI units are to be regarded as thestandard. The values given in parentheses are for informationonly.1.3 This standard does not purport to address all of thesafety concerns, if any, associated with its use. It is theresponsibility of the user of this standard to establish appro-priate safety and health practices and determine the applica-bility of regulatory limitations prior to use.2. Referenced Documents2.1 ASTM Standards:2D4483 Practice for Evaluating Precision for Test MethodStandards in the Rubber and Carbon Black ManufacturingIndustriesF538 Terminology Relating to the Characteristics and Per-formance of Tires3. Terminology3.1 Definitions:3.1.1 inflation pressure loss rate, n—rate of change ofnormalized inflation pressure, determined from the slope of thelinear portion of the log pressure versus time curve. F5383.1.2 measured inflation pressure, n—gauge pressure of atire measured at a given time under ambient temperature andbarometric pressure. F5383.1.3 normalized inflation pressure, n— measured pressureof a tire adjusted, according to the ideal gas law, to the nominaltest temperature and one atmosphere external barometricpressure. F5384. Summary of Test Method4.1 Test tires are mounted on rims, fitted with calibratedprecision pressure measuring devices, inflated to the desiredpressure, and, after a period of stabilization, are monitored forinflation pressure as a function of time under static, constanttemperature conditions.4.2 Measured inflation pressures are normalized to thenominal test temperature and one atmosphere barometricpressure for calculation of pressure loss rates.4.3 Two or more tires per tire specification are tested forpressure loss rate over a period of two to six months. Highprecision in the equipment and data may allow shortening thetest. See 9.6, 10.5, and Section 12.4.4 The pressure loss rate is calculated as percent loss permonth at the nominal test temperature and one atmospherebarometric pressure (101.3 kPa).5. Significance and Use5.1 Inflation pressure retention is an important property oftire performance because underinflation can adversely affecttire rolling resistance, handling, structural integrity, and treadlife.5.2 This test method is useful for research and developmentevaluation of the effects of tire component formulations andgeometry on inflation pressure retention. Testing for rate ofpressure loss under static conditions is practical because of thefollowing:5.2.1 Tires in normal use are predominantly at rest, and5.2.2 Relative air diffusion rates of various tires in normalintermittent road service will correlate with static relative rates,to a first approximation. The relative air diffusion rates ofdifferent tires may not be quite the same under dynamic flexingas when tested statically, but the difference is believed to besmall.5.3 The results from this test method are not suitable forinferring tire inflation retention under severe service1This test method is under the jurisdiction of ASTM Committee F09 on Tiresand is the direct responsibility of Subcommittee F09.30 on Laboratory (Non-Vehicular) Testing.Current edition approved Dec. 1, 2010. Published March 2011. Originallyapproved in 1987. Last previous edition approved in 2006 as F1112 – 06a. DOI:10.1520/F1112-06AR10.2For referenced ASTM standards, visit the ASTM website, www.astm.org, orcontact ASTM Customer Service at service@astm.org. For Annual Book of ASTMStandards volume information, refer to the standard’s Document Summary page onthe ASTM website.Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States1conditions, such as heavy cornering or impacts, that mightcause significant air loss at the tire-rim seal.6. Interferences6.1 Ambient temperature excursions greater than 63°C(65°F) for several hours may significantly alter both the airdiffusion rate through the tire and the driving force inflationpressure, thereby causing variability in the rate of tire pressureloss. Some temperature variations can result from inconsistentair currents around the test tires, or from spatial temperaturegradients in static air spaces. The effects can be significantwhere heat-generating tests such as laboratory road wheels areoperating intermittently in the same room.6.2 Other causes for inconsistent results are minute leaks inthe tire, rim, valve, or pressure measuring device assembly; aswell as varied service or other heat history of the test tires.7. Sampling and Preparation of Test Tires7.1 All of the tires in a sample should have the desiredproducing plant and date codes and similar storage and servicetemperature history.7.2 Tires must be free of molding or other defects, particu-larly on the bead area and innerliner surfaces.7.3 New tires should be used for evaluation of constructionor compound variations.7.4 Minimum recommended sample size is two tires foreach type of tire or treatment being tested.7.5 Test tires are to be mounted on rims of the proper beadseat diameter with clean, smooth surfaces in the bead seatareas, particularly in the vicinity of the weld. Rim flanges mustbe free of sharp edges or scuffs that could damage the tireduring mounting. Bead seat diameters must be verified using acertified disc tape (a.k.a. ball tape) and be acceptable accordingto an applicable standard such as the Tire transducer, cabling,signal conditioner, and data acquisition device. These systems,along with stable environmental conditions, can enable shorterduration tests producing results comparable to 180-day testresults.7.11 Inflate the tire-rim assembly outfitted with the pressuregauge or transducer to the desired starting pressure. Test forleaks by submersion in a water tank, up to the base of the gaugeor transducer, for at least 30 min or carefully check both beadsand fittings for leaks with leak detection fluid. If other than apainted steel rim is used, the entire rim must be checked forleaks.7.12 After confirming that the tire-rim assembly is free fromleaks, fit the valve or adapter opening with a sealing cap, andkeep the tire in the same orientation to avoid causing newleaks.7.13 After the leakage check, condition the tires at the testroom temperature for 48 h; then adjust to the starting testpressure. Replace the sealing cap on the valve or adapter. If apressure drop of more than 3 kPa (0.5 psi) occurs over theconditioning period, recheck the assembly for leakage accord-ing to 7.11 and, if necessary, dismount and remount the tire.Greater than 48 h conditioning may be necessary for some tiressuch as high-pressure compact spares, whose growth can affectearly inflation loss results.8. Test Chamber8.1 The test chamber shall be controlled to provide a meanambient temperature that is within 60.6°C (61°F) of thenominal test temperature and with overall variation within63°C (65°F) over the course of the test.8.2 Nominal test temperatures currently in use are: 21, 24,30, and 38°C (70, 75, 86, and 100°F).8.3 Air in the test chamber should be forcibly circulated tominimize spatial temperature gradients.9. Procedure9.1 Place the test tires in the test chamber so as to allow freeair circulation around them and easy visual access to thepressure gauges. The tires shall not be moved during the test.3Available from Rubber Manufacturers Association, 1400 K. St. N.W.,Washington, DC 20005.F1112 − 06a (2010)29.2 Record inflation pressures, concurrent ambienttemperatures, and barometric pressures frequently (daily read-ings are recommended) for two weeks. If using a pressuregauge, tap the gauge lightly prior to each reading.Tires shall beconsidered to be satisfactorily conditioned when the slope ofthe logarithm of the normalized inflation pressure versus timerelationship becomes constant.9.3 The test shall be continued if replicate tires agree witheach other within 6 kPa (approximately 1 psi) inflation pressureafter two weeks. Otherwise, recheck the suspect assembly forleaks according to 7.11, and restart the test.9.4 Inflation pressure readings and concurrent ambient tem-perature and barometric pressure readings shall be recorded atleast once per week during the remaining test period. Continu-ous monitoring of ambient temperature is desirable to ensurethat the tire is at equilibrium temperature when its pressure ismeasured.9.5 Correct inflation pressure readings, P1, to the nominaltest temperature and one atmosphere barometric pressure(101.3 kPa, 14.69 psi) by using the equation in 10.1.9.6 A commonly used test duration is 180 days. The testperiod may be shorter or longer depending on the precisionlevel of the data. More frequent or continuous electronicmeasurements are recommended if shorter term projections ofperformance are intended. See also 4.3.10. Calculation10.1 Calculate normalized pressures from the formula:P 5 ~P11B1!~T2/T1! 2 B2(1)where:P = normalized inflation pressure, kPa,P1= measured inflation pressure, kPa,B1= measured barometric pressure, kPaB2= reference barometric pressure, kPa (one atmo-sphere = 101.3 kPa),T1= measured temperature, °K, andT2= nominal test temperature, °K.NOTE 1—Temperature in Kelvin equals Celsius plus 273.15.10.2 Air permeation data fits the model of the followingform:P 5 Poeβt(2)where:P = normalized pressure, kPa,Po= normalized initial pressure, kPa,β = loss rate per day at the nominal test temperature, andt = test time, days.10.3 A least squares fit can be obtained after transformationof the model equation to the following form:lnP 5 α1βt (3)where:α =lnPoThe model is derived from a relationship that expressespressure loss as a function of pressure only:dP/dt 5 βP (4)Thus, pressure loss in absolute units will vary as the actualnominal pressure changes, but a loss rate can be expressed bythe constant, β.10.4 The calculated loss rate constant, β, will be in units of1/day. This number will typically be a very small decimal; it isconvenient, and perhaps more intuitively meaningful, to ex-press loss rate as a percent per month. This is done bymultiplying β by 3000 (which is 100%×30days/month).10.5 Calculations of steady state loss rate and predictions offuture pressures can be made from any point in the test (beyondthe first 30 days as explained in X1.3). The accuracy of suchpredictions will depend on the appropriateness of the model aswell as the precision level of data obtained that, in turn, willdepend on factors such as the following:10.5.1 Care in reading pressure gauges,10.5.2 Resolution and accuracy of pressure measuringdevices,10.5.3 Maintenance of a relatively constant temperature,and10.5.4 Frequency of pressure measurements.11. Report11.1 For each test tire, report the loss rate as a percent permonth (β × 3000) and other pertinent test parameters includ-ing:11.1.1 Total test duration in days,11.1.2 Projected inflation pressure, if applicable,11.1.3 Average ambient temperature and range over test,11.1.4 Initial inflation pressure,11.1.5 Actual and “best fit” final inflation pressure, and11.1.6 Starting date.11.2 Also report the manufacturer, line, size, and U.S. Dept.of Transportation (DOT) serial number for each tire.11.3 An example treatment of test data is given in AppendixX1.12. Precision and Bias12.1 The precision and bias section has been prepared inaccordance with Practice D4483. Refer to this for terminologyand other statistical calculation details.12.2 An interlaboratory test was conducted in 1985 using aset of used uniform tire quality grading (UTQG) CourseMonitoring Tires (CMT). This set of ten tires was furnished byone of the participating laboratories.12.3 Five laboratories participated in the interlaboratorytest. Each laboratory tested two tires following the test proce-dure as outlined in this test method. Thus, there are only 5degrees of freedom (df) for repeatability (r) and four df forreproducibility (R). These low df for r and R are not optimumfor a good reliable estimate of overall precision.12.4 The tire air pressure loss rate was measured simulta-neously for each of the two tires (per laboratory) at 22 6 0.8°C.This loss rate, as specified by this test method, is expressed as(B × 3000) in units of percent per month (or 30 days) at 1 atm(101.3 kPa) barometric pressure. A test result is the valueobtained for (B × 3000) for one tire and one test on that tire.F1112 − 06a (2010)312.5 The precision results, given in Table 1, show that therepeatability is equal to the reproducibility. For this (small df)interlaboratory test, the variation among the five laboratories isno greater than the pooled tire-to-tire variation within thelaboratories. The rather large relative repeatability of 35.4 %may be indicative of variations in the test samples themselves.There is no independent way to verify this due to the agedependency of diffusion rate measurements.12.6 Table 2 lists the actual test results. Inspection of thetable shows the lack of agreement between duplicate tireresults within any one of the five laboratories. It also showshow the level of agreement among the laboratories substan-tially improves by taking averages. The pooled, within-laboratory single tire standard deviation, Sr, of 0.24 is twice thebetween-laboratory single tire standard deviation of 0.12, SR(adjusted for the “averages of two basis” by multiplication by=2).12.7 Repeatability—The repeatability, r, of this test methodhas been established as 0.68. Two single test results, that is,loss rate in percent/month at 1 atm (101.3 kPa), obtained undernormal test method procedures, that differ by more than this rmust be considered as derived from different or nonidenticalsample populations.12.8 Reproducibility—The reproducibility, R, of this testmethod has been established as 0.68. Two single test results,that is, loss in percent/month at 1 atm (101.3 kPa), obtained intwo different laboratories, under normal test methodprocedures, that differ by more than R must be considered tohave come from different or nonidentical sample populations.12.9 Repeatability and reproducibility expressed as a per-cent of the mean level, (r) and (R), have equivalent applicationstatements as above for r and R. For the (r) and (R) statements,the difference in the two single test results is expressed as aperc