Interpretation ID: 86-4.50

TYPE: INTERPRETATION-NHTSA

DATE: 08/19/86

FROM: LYNNE L. KEIL -- MANAGER, MATERIALS AND EQUIPMENT - CITY OF BILLINGS, MONTANA

TO: WCS SPRUNK -- MANAGER, SAF-TEE SIPING, INC.

TITLE: NONE

ATTACHMT: DECEMBER 30, 1988 LETTER FROM JONES TO SPRUNK, OCTOBER 8, 1987 LETTER FROM SPRUNK TO JONES, BROCHURES ON TIRE SIPING, 1978 NSC WINTER TEST REPORT, ARTICLE FROM AUGUST 1986 ISSUE OF "SCHOOL BUSINESS AFFAIRS," ARTICLE ENTITLED "SLASHING TIRES FOR SAFETY AND SAVINGS" FROM DECEMBER 1984 "NATIONAL SCHOOL BUS REPORT," MARCH 20, 1985 LETTER FROM GIFFORD TO SPRUNK, OCTOBER 15, 1982 LETTER FROM PALMER TO MARCY MANUFACTURING, AND APRIL 1983 AND APRIL 1984 ARTICLES FROM "GW SAFETY TALK"

TEXT: This is written in accordance with your request that we document the results experienced as a consequence of siping tires to increase handling performance on certain vehicles. Last year, we were experiencing severe handling problems on snow and ice with police vehicles in particular.

Approximately 20 patrol cruisers had been fitted with new Good Year Eagle GT Tires. With these tires, cornering and stopping on ice and snow was hazardous and in some instances, impossible. In an effort to improve performance, we siped the tires on several of these vehicles and ran tests.

On the test vehicles, we found that we could negotiate 90 degrees corners safely on ice at 25 to 30 miles per hour - after siping. Prior to siping, we could corner and maintain vehicle control only at speeds under 10 miles per hour. Braking efficiency was increased in all cases by 30 percent.

Given the inclemental weather and tire type, siping in this case was obviously necessary and functional. It was also a great deal less costly than replacing 20 sets of tires. We have since siped tires on Met Transit coaches with very good results. Should you have any questions, or wish further information, please do not hesitate to contact me. Thank you.