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AN ANALYSIS OF BEAD COMPRESSION GROOVES

AN ANALYSIS OF BEAD COMPRESSION GROOVES. By Dennis Carlson and John Warren Taylor. WHAT IS A COMPRESSION GROOVE?. Compression Grooves . Deep Compression Grooves Have Been Associated with Over-deflection(OD) and Tire Bead Design for Decades

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AN ANALYSIS OF BEAD COMPRESSION GROOVES

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  1. AN ANALYSIS OF BEAD COMPRESSION GROOVES By Dennis Carlson and John Warren Taylor

  2. WHAT IS A COMPRESSION GROOVE?

  3. Compression Grooves • Deep Compression Grooves Have Been Associated with Over-deflection(OD) and Tire Bead Design for Decades • Early Bead Designs Did Not Control Compression Groove Growth and Failures Occurred • Design Changes “Cured” this Problem-Chafers, Protectors, Turn-up Designs and Stiff Flippers

  4. “Severe Bead Chafing” from a Late 1970’s RMA Book

  5. Patents to Control Compression Grooves

  6. Patents, Cont.

  7. Patents, cont.

  8. WHY DO CG’S FORM ? • The Flange Area is an Area of High Compression Stresses (Hinge Point) • The CG’s Form Due To Compression Set of the Rubber Over Time • There Can Also Be a Small Amount of Chaffing (movement) • The Sidewall “Bends” Outward in the Footprint-This Increases The Stress

  9. WHAT DOES A COMPRESSION GROOVE LOOK LIKE?

  10. Another example

  11. And Another

  12. Analysis of Compression Grooves-Procedure • 75 tires were run by the DOT as part of the UTQG (Unified Quality Grading System) Wear Test (see CFR 49 575.104) • These tires were run for ≈7200 miles. • Tire pressures were checked 3 times a day. • In short, these tires were run under ideal conditions of usage. • After the test, the compression grooves were measured.

  13. The Compression Grooves Were Measured with a Digital Caliper-Width and Depth

  14. Tests of Measurement Technique • A Plaster Cast Was Made of the CG Region-Measurements Agreed • Profilometer -Measurements Agreed • Repeatability-18 Measurements Taken in the Same Area by a Semi-skilled Person-Coefficient of Variation ≈ 9% for Depth and 4% for the Width Measurement

  15. Profilometer

  16. Results-All Tires Had CG’s • WIDTH DEPTH • MAXIMUM 0.316" 0.113" • MINIMUM 0.001" 0.001" • AVERAGE 0.156" 0.023"

  17. ALL TIRES HAD COMPRESSION GROOVES

  18. Biggest Differences Were Between Tire Manufacturers • Michelins had the smallest- Average Width of .085” and Depth of .016” • Goodyears had Average Width of .210” and Depth of .031” (Kelly-Springfields were slightly larger but the sample size was smaller and KS is a part of GY)

  19. Importance of Compression Grooves? • In the old days, bead durability was an important issue. Tires could fail prematurely in the bead. • In modern tires, this is not an important issue. • Compression Grooves are used by some as an indicator of over-deflection.

  20. Mis-Use of Compression Grooves-1 • “Any Compression Groove Indicates Over-Deflection” • Fact-Compression Grooves are developed under normal operating conditions. • Sources –This Paper, the Cottles Paper and the Standard Testing Laboratory (STL) paper.

  21. Mis-Use of Compression Grooves-2 • “CG’s are a good indicator of over-deflection” • Fact-Because tires develop CG’s under normal conditions and the wide variation between manufacturers, CG’s are a poor indicator of over-deflection.

  22. Mis-Use of Compression Grooves-3 • “GC’s equal Over-deflection(OD) Equals Tread-Belt Separations” • Most of the Tests That Have Been Run to Show the Link Between CG’s and OD Do Not Separate the Tires. • The Standard Testing Laboratory (STL) Test Did Fail Tires But After ≈9000 miles of extreme OD. Other Tires went 20000 miles Without Failure. The Failure Mode was Not Given.

  23. Mis-Use of Compression Grooves-3cont. • The Amount of OD in the Most Severe STL Test was Equivalent to Loading a Car to GVWR and Then Putting an Additional 23 People in the Car. Some Tires Lasted 20000 miles • What Good is This Indicator?

  24. STL DATA - RAW • STL Bead Groove Study Subjective Ratings • Tire Size= P205/70R14 • Load(lbs) Pressure(psi) T&RA % Subjective Rating Width Depth Mileage • New Rim • 1433 35 100 1.5 20000 • 1628 35 114 1 20000 • 1055 26 85 1 20000 • 1199 26 97 1.5 20000 • 1403 26 113 0.75 20000 • 1628 26 131 3 0.24 0.05 20000 • 2017 26 163 5 0.35 0.11 20000 • 1199 20 110 1.5 20000 • 1628 20 149 3.5 0.26 0.06 20000 • Modified Rim • 1628 35 114 1 20000 • 1199 26 97 1.5 20000 • 1403 26 113 1 20000 • 1628 26 131 2 0.17 0.04 20000 • 2017 26 163 2.5 0.2 0.06 10150 • 1199 20 110 1.5 20000 • 1628 20 149 3 0.26 0.06 15600

  25. STL DATA- Sorted • Same Data Sorted by Severity of Condition • Load(lbs) Pressure(psi) T&RA % Subjective Rating Width Depth Mileage • New Rim • 1055 28 85 1 20000 • 1199 26 97 1.5 20000 • 1199 20 110 1.5 20000 • 1403 28 113 0.75 20000 • 1433 35 100 1.5 20000 • 1628 35 114 1 20000 • 1628 26 131 3 0.24 0.05 20000 • 1628 20 149 3.5 0.26 0.06 20000 • 2017 26 163 5 0.35 0.11 20000 • Modified Rim • 1199 26 97 1.5 20000 • 1199 20 110 1.5 20000 • 1403 26 113 1 20000 • 1628 35 114 1 20000 • 1628 26 131 2 0.17 0.04 20000 • 1628 20 149 3 0.26 0.06 15600 • 2017 26 163 2.5 0.2 0.06 10150

  26. Future Investigations • Deep Wheel Weight Impressions- So far appears to be from bad WW installation • Wheel Flange Paint Loss- Seems to be universal with all steel wheels.

  27. Deep Wheel Weight Impressions

  28. Deep Wheel Weight Impressions

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