Transcript 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
• 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 GroovesProcedure
• 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 CaliperWidth and Depth
Tests of Measurement Technique
• A Plaster Cast Was Made of the CG RegionMeasurements Agreed
• Profilometer -Measurements Agreed
• Repeatability-18 Measurements Taken in the
Same Area by a Semi-skilled PersonCoefficient of Variation ≈ 9% for Depth and 4%
for the Width Measurement
Profilometer
Results-All Tires Had CG’s
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MAXIMUM
MINIMUM
AVERAGE
WIDTH
0.316"
0.001"
0.156"
DEPTH
0.113"
0.001"
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 OverDeflection”
• 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 TreadBelt 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.
• 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
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STL Bead Groove Study Subjective Ratings
Tire Size= P205/70R14
Load(lbs)
New Rim
1433
1628
1055
1199
1403
1628
2017
1199
1628
Pressure(psi)
T&RA %
Subjective Rating Width
35
35
26
26
26
26
26
20
20
100
114
85
97
113
131
163
110
149
1.5
1
1
1.5
0.75
3
5
1.5
3.5
Modified Rim
1628
35
1199
26
1403
26
1628
26
2017
26
1199
20
1628
20
114
97
113
131
163
110
149
1
1.5
1
2
2.5
1.5
3
Depth
0.24
0.35
0.05
0.11
0.26
0.06
0.17
0.2
0.04
0.06
0.26
0.06
Mileage
20000
20000
20000
20000
20000
20000
20000
20000
20000
20000
20000
20000
20000
10150
20000
15600
STL DATA- Sorted
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Same Data Sorted by Severity of Condition
Load(lbs)
New Rim
1055
1199
1199
1403
1433
1628
1628
1628
2017
Pressure(psi)
T&RA %
Subjective Rating Width
28
26
20
28
35
35
26
20
26
85
97
110
113
100
114
131
149
163
1
1.5
1.5
0.75
1.5
1
3
3.5
5
Modified Rim
1199
26
1199
20
1403
26
1628
35
1628
26
1628
20
2017
26
97
110
113
114
131
149
163
1.5
1.5
1
1
2
3
2.5
0.24
0.26
0.35
0.17
0.26
0.2
Depth
Mileage
0.05
0.06
0.11
20000
20000
20000
20000
20000
20000
20000
20000
20000
0.04
0.06
0.06
20000
20000
20000
20000
20000
15600
10150
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