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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

AN ANALYSIS OF BEAD COMPRESSION GROOVES

By Dennis Carlson and

John Warren Taylor



Compression grooves
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






Why do cg s form
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





Analysis of compression grooves procedure
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.



Tests of measurement technique
Tests of Measurement Technique Caliper-

  • 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


Profilometer
Profilometer Caliper-


Results all tires had cg s
Results-All Tires Had CG’s Caliper-

  • WIDTH DEPTH

  • MAXIMUM 0.316" 0.113"

  • MINIMUM 0.001" 0.001"

  • AVERAGE 0.156" 0.023"



Biggest differences were between tire manufacturers
Biggest Differences Were Between Tire Manufacturers Caliper-

  • 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)


Importance of compression grooves
Importance of Compression Grooves? Caliper-

  • 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.


Mis use of compression grooves 1
Mis-Use of Compression Grooves-1 Caliper-

  • “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.


Mis use of compression grooves 2
Mis-Use of Compression Grooves-2 Caliper-

  • “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.


Mis use of compression grooves 3
Mis-Use of Compression Grooves-3 Caliper-

  • “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.


Mis use of compression grooves 3 cont
Mis Caliper--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?


Stl data raw
STL DATA - RAW Caliper-

  • 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


Stl data sorted
STL DATA- Sorted Caliper-

  • 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


Future investigations
Future Investigations Caliper-

  • 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.




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