Compression Rim Grooving-- An Objective Measurement Technique By Troy Cottles What started in 2006 as a large tire testing undertaking has in part led to this presentation today. Presented at the HIFI Tire Tech Conference, Houston, TX August 13, 2010

Compression Rim Grooving- Background: Prior studies Methodology Subjectivity Precision Having reviewed the available literature on tire and rim compression rim grooving, and finding that the major studies were conducted with an objective of analyzing a tire run in the under-inflated state, I had some problems with the methodology and the limitations presented by the measurement technique—where one was actually employed. As to methodology: The first STL study presented June 1997 found no measurable grooves (width or depth) in either set of tires being tested under proper inflation and under varying loads. The second and third STL studies presented October 1997 and September 1998, respectively, fail to measure the groove depths. Rim groove severity was determined subjectively by rank ordering visual amount observed and photographed on a 0 to 5 scale. Proper scientific methodology requires that any observer should be able to duplicate the measured results [the repeatability test]. Subjective evaluation does not typically allow for repeatability and therefore does not support [objective data collection]. Abandoning the groove depth measurements in successive studies and failing to record rim groove measurements under proper inflation pressure conditions suggests (at the least) the existing studies lacked a means to collect precise measurement values.

Compression Rim Grooving- Background: Objective Measurement Technique: Objective Measurement Technique: An EyeCon line laser was purchased from LMI. The laser was calibrated using block gauges. The laser is operated from a computer using LMI software to capture an image. New tires were purchased. As a baseline the rim flange areas were scanned and the images were stored. An additional laser software program was generated in order to be able to compare one image to another. Through this program before and after laser images can be compared and by selecting points on either image the program outputs a digital value for the actual groove depths.

Compression Rim Grooving- Background: Test Protocol: CONTROL REDUCED-INFLATION Inflation Pressure: 30 PSI 21 PSI Load: 890 lbs 890 lbs Rim: 14 X 5.5 14 X 5.5 Speed: 75 mph 75 mph Duration: 40,000 miles 40, 000 miles Test Protocol: 12 different brands/types of tires were selected for this and other testing. The tire size selected was 185/70R14. Several tires of each brand were purchased. Tires were photographed and laser scanned in the new condition. Tires were shipped to Smithers Scientific and ultimately to STL to complete the drum testing. Tires were tested in two groups: control and reduced-inflation. The reduced-inflation tires were included in order to validate the test protocols—meaning if no grooves were observable on the reduced-inflation set, then the control tire data would have been suspect. After confirming the reduced-inflation tires were in fact grooved, they were set aside and the control tires (the focus of this study) were analyzed. Upon return the tires were rescanned by laser and then overlaid to the original images. In the most significant instances the groove depth values were depicted on the overlay bitmap images.

Compression Rim Grooving- Background: Test Tires: Yokohama Aspec A300, H-rated, FD3505 Bridgestone B700AQ, T-rated, 2R3605 Dunlop Sp Sport LM701, H-rated, EU4005 Dayton Quadra SE, S-rated, HY2105 Firestone FR690, S-rated, W22805 Uniroyal Tiger Paw, S-rated, K41605 Hankook Radial H714, S-rated, 1G1405 Michelin Symmetry, S-rated, HN1204 Toyo Spectrum, S-rated, 9T5004 Federal Supersteel 735, T-rated, 2E4905 Cooper Lifeliner SLE, T-rated, U94305 Dunlop SP20FE, S-rated, M63605 Test Protocol: 12 different brands/types of tires were selected for this and other testing. The tire size selected was 185/70R14. Several tires of each brand were purchased. Tires were photographed and laser scanned in the new condition. Tires were shipped to Smithers Scientific and ultimately to STL to complete the drum testing. Tires were tested in two groups: control and reduced-inflation. The reduced-inflation tires were included in order to validate the test protocols—meaning if no grooves were observable on the reduced-inflation set, then the control tire data would have been suspect. After confirming the reduced-inflation tires were in fact grooved, they were set aside and the control tires (the focus of this study) were analyzed. Upon return the tires were rescanned by laser and then overlaid to the original images. In the most significant instances the groove depth values were depicted on the overlay bitmap images.

Compression Rim Grooving- Control Tires: New Tire Photos-Tire #28 Uniroyal Tiger Paw

Compression Rim Grooving- Control Tires: New Tire Laser Profile-Tire #28 Uniroyal Tiger Paw

Compression Rim Grooving- Control Tires: Tire Photos After Test-Tire #28 Uniroyal Tiger Paw

Compression Rim Grooving- Control Tires: Laser Overlays-Tire #28 Uniroyal Tiger Paw

Compression Rim Grooving- Conclusions: Tire designers calculate bead compression values when tires are being designed and developed. Without bead compression the tire would not fit properly to the rim, possibly lose air, slip on the rim or de-bead. Previous studies have concluded that rim grooves are produced by under-inflated operation.  This study demonstrates that rim grooves can be produced even under proper inflation and load conditions. Twelve control tires of different brands, manufacturing facilities, tire constructions, rubber compounds and properties, amounts of rubber gauge in the bead flange area, and various bead contour designs were operated on laboratory drum machines under the same loads, inflation pressures, and speeds where the variable of how often someone might check their tire pressure on their personal vehicle was eliminated from consideration. Given many of the mentioned differences in the control tires, the rim grooves generated varied from just perceptible to clearly-defined as to rim groove depth. The notion that the mere presence of a rim groove could serve as the sole indicator of tire under- inflated operation for a consumer is itself not useful or practical, since the tire would have to be removed from the rim in order to view the area in question. The notion that the mere presence of a rim groove could serve as the sole indicator of tire under- inflated operation for a proper forensic analysis is likewise unreliable as an indicia of that condition given the range of rim grooves presented in the control tires in this test. It is possible to evaluate rim grooves (and other contour changes to tires) through the objective, high- precision, non-contacting, quantifiable means of laser scan imaging as demonstrated in this study.