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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

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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

  • 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


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


Patents to Control Compression Grooves


Patents, Cont.


Patents, cont.


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


WHAT DOES A COMPRESSION GROOVE LOOK LIKE?


Another example


And Another


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.


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


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


Profilometer


Results-All Tires Had CG’s

  • WIDTHDEPTH

  • MAXIMUM0.316"0.113"

  • MINIMUM0.001"0.001"

  • AVERAGE0.156"0.023"


ALL TIRES HAD COMPRESSION GROOVES


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)


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.


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.


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.


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.


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?


STL DATA - RAW

  • STL Bead Groove Study Subjective Ratings

  • Tire Size=P205/70R14

  • Load(lbs)Pressure(psi)T&RA %Subjective RatingWidthDepthMileage

  • New Rim

  • 1433351001.520000

  • 162835114120000

  • 10552685120000

  • 119926971.520000

  • 1403261130.7520000

  • 16282613130.240.0520000

  • 20172616350.350.1120000

  • 1199201101.520000

  • 1628201493.50.260.0620000

  • Modified Rim

  • 162835114120000

  • 119926971.520000

  • 140326113120000

  • 16282613120.170.0420000

  • 2017261632.50.20.0610150

  • 1199201101.520000

  • 16282014930.260.0615600


STL DATA- Sorted

  • Same Data Sorted by Severity of Condition

  • Load(lbs)Pressure(psi)T&RA %Subjective RatingWidthDepthMileage

  • New Rim

  • 10552885120000

  • 119926971.520000

  • 1199201101.520000

  • 1403281130.7520000

  • 1433351001.520000

  • 162835114120000

  • 16282613130.240.0520000

  • 1628201493.50.260.0620000

  • 20172616350.350.1120000

  • Modified Rim

  • 119926971.520000

  • 1199201101.520000

  • 140326113120000

  • 162835114120000

  • 16282613120.170.0420000

  • 16282014930.260.0615600

  • 2017261632.50.20.0610150


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.


Deep Wheel Weight Impressions


Deep Wheel Weight Impressions


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