Interpretation ID: 86-4.31

TYPE: INTERPRETATION-NHTSA

DATE: 08/01/86 EST

FROM: SCHOOL BUSINESS AFFAIRS

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, AUGUST 19, 1986 LETTER FROM KEIL TO SPRUNK, 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: The school bus industry is quite possibly the most safety conscious industry in the nation, and properly so. Newspaper accounts of school bus accidents evoke a greater sense of tragic loss amongst readers -- no matter how far away the accident -- than most disasters involving greater numbers. Our culture assigns greater priority to the lives of its children than to the rest of us. Thus, any measures that enhance the safety of school bus passengers deserve serious attention, and they usually get it.

That was the case with the transportation director of a school district in Iowa when he happened on some literature which described a bizarre-sounding, after-purchase procedure for slashing tires. Jerry Williams puzzled about the procedure (called "siping") for a while, checked around with other companies which slashed their tires, and persuaded the business manager of the Linn-Mar Community School District to buy a siping machine.

That was in 1978. Williams says, "we've been very happy with it ever since."

The siping machine Jerry Williams uses can put any cut in virtually any kind of tire siped, new or used, as long as it has 5/32" tread left. Anyone can be trained to use the machine in 10 or 15 minutes, and the machine allows an operator to make cuts of different depths, as required by the amount of tread left on tire. Cuts may be on the diagonal or straight across the tire, and the width between them may be varied. The cutting blades on this particular sipe are cooled by a spray-miser which cost about five dollars, and are good for 80 or 90 tires. Williams sharpens his blades after 20 tires -- "I touch them up," as he puts it.

Siping has been around for a long time, but only in the last decade or so has there been a machine which makes the tiny cuts quickly, effectively and inexpensively. Williams reports that "it takes two hours to sipe the six tires on my buses, from the time the bus comes in until it's turned loose. That's with a crew of two people."

The Linn-Mar School District's siping machine is manufactured by the Saf-Tee Siping & Grooving Company of Minnetonka, Minnesota.

In Missoula, Montana, in the mountainous western part of the state, Bob Beach's school bus fleet of 70 buses travels 800,000 miles per year, all on siped tires. Before the Saf-Tee Siper was invented, Beach used to cut his tires by hand, with a knife, but it was a costly and ragged procedure.

With the machine-made cuts, according to Beach, the hundreds of sharp little edges created by siping make the footprint of a tire spread, and "this means the tire grips the road surface better, making braking and steering on snow or ice much more effective." He adds, "you also get much better traction spin for starts."

The Linn-Mar School District used to stud their tires for winter road conditions, but siping has eliminated the need for studs and double tire inventories.

According to Williams, Linn-Mar first siped its school bus tires in the dead winter. Roads were covered with snow and ice. As an experiment, he mentioned to some drivers that their tires had been siped, but said nothing to the others. "When the latter came back in the afternoon," he continued, "the drivers said "What did you do to his bus? The front end didn't slide around the corners like it did in the past, and the stopping distance is shorter. And it's getting better traction on take-off."

In Montana, Bob Beach used to run his siped tire only in the winter, but when he began using them year-round, he discovered that siped tires are very effective in Montana's June and September rains.

"The siped tread-elements open up and the sharp edges penetrate the lubricating film of water in what might be called a squeegee action, and the openings between the tire elements created by the sipes channel water away. This minimizes hydroplaning. In fact, it usually eliminates hydroplaning altogether."

Bill Dufor, who operates a fleet of 165 school buses in Prospect, Connecticut, and Pittsfield, Massachusetts, agrees with Beach. "One of the reasons we've got a siping machine is because of wet roads. We feel a lot more comfortable with them, especially with some re-caps which are noted for being a little bit slick on wet roads. Siped tires give you that much more comfort and reliability. We think it does a good job on wet roads."

You might reasonably think that tire life would be reduced by siping; tire engineers though so too, a couple of decades ago. To their surprise, however, they found that tire life increased, and for a very simple reason: siped tires run cooler. The cuts help dissipate heat. Siped tires are used by school bus fleets, highway patrol cars, over-the-road truckers, transit companies and thousands of passenger car owners. In all cases, tires run cooler, and some users report increases in tire life from 15 to 20 percent. That reduces operating costs, and is of obvious significance for public sector fleet owners, like school districts.

The Linn-Mar School District runs siped highway tires on the front end and siped traction tires on the rear -- "Michelins, Goodyears, Fire-stones," according to Williams. The bottom line about siping tires? In Jerry Williams' words, "Everybody feels safer."

That is the case with Bob Beach and Paul Dufour, as well. Siped tires are not only safer on roads that are icy, snow-packed or filmed with water, they are also cost-effective even on dry roads. They run cooler and dissipate heat.

As Bob Beach puts it, "increased safety and reduced operating costs don't always go together, but with machine-siped tires, they do. There's no way I'd go back to running without them."