pp-bead compression

measlyincompetentUrban and Civil

Nov 29, 2013 (3 years and 8 months ago)

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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





















WIDTH


DEPTH




MAXIMUM


0.316"


0.113"




MINIMUM


0.001"


0.001"




AVERAGE


0.156"


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
-
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











STL Bead Groove Study Subjecti ve Rati ngs









Ti re Si ze=

P205/70R14


























Load(l bs)

Pressure(psi )

T&RA %

Subjecti ve Rati ng

Wi dth

Depth

Mi l eage



New Ri m









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












Modi fi ed Ri m









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











Same Data Sorted by Severi ty of Condi ti on









Load(l bs)

Pressure(psi )

T&RA %

Subjecti ve Rati ng

Wi dth

Depth

Mi l eage



New Ri m









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












Modi fi ed Ri m









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


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