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Why motorcycle tires don' make sense A look at the motorcyclelire marketplace By Jim Wolcott The speed game One of the major selling points for modern motorcycle tires is the socalled speed rating. The CUTTent speed rating system for motorcycle tires was originated by the European Tire and Rim Technical Organization (ETRTO), and was designed to describe the maximum speed that a motorcycle tire could safety sustain. For the roads of Europe, this is an important figure. Many highways, 14 particularly the Autobahns of Germany, have virtually no speed limits. The testing procedure suggested by the ETRTO was simple: mount the tire on a representative rim, properly inflate the tire and give it a representative weight load, and rotate the tire against a large steel drum. The tire would then be rotated at gradually increasing speeds until it "failed." The heat generated within the tire at high speeds would eventually cause the component parts of the tire to delaminate, where the tread rubber separates from the cord structure. On the basis of this test, the tire would be awarded a letter grade to correspond to the highest speed that a particular tire can safely withstand. This testing system has become the . subject of considerable controversy. First of all, the ETRTO never exactly defined what was considered to be a "sustained" speed. Some manufacturerschoose to interpret this to mean: "sustained for the life of the tire." Others shamelessly perceive it to mean: "sustained for 30 seconds." Unfortunately, the ETRTO has merely suggested this standard, and, as an organization, has no legal clout to enforce the speed rating system (as does, for example, the Snell Foundation·for iu helmet standards)..Worse, . the ETRTO doesn't actually perform tests on individual tires. Testing is performed by the tire manufacturers. Compliance is voluntary. There is a widespread misqmception that since all motorcycle tires sold for street use must be approved by the Department of Transportation (DOT), that the DOT actually performs these high-speed tests. ot so. The DOT does specify a "high speed" test- again, described in ection 119 of the Federal Motor Vehicle Safety Standard. The test? To mount the tire on a representative rim, inflate the tire as indicated on the sidewall, load the tire to 85% of its load rating, warm the tire to 95°, and run the tire at gradually increasing speed to where it is run for 30 minutes at 85 mph -well below the lowest speed of the European speed rating system! Surprisingly, even with this lowly 85 mph test, all the DOT actually does is to specify the testing procedure; the DOT does not conduct the test on each and every tire offered for sale. The standard is set, the manufacturer is expected to comply, and the DOT intervenes only when there is some evidence that a particular tire is unsafe. As you might expect, this situation invites fraud and abuse. The July 6, 1983 issue of the German magazine Das Motorrad carried a story concerninga pair of llOOccSuzuki Katanas equipped with Pirelli Phantom tires. The machines were taken on a day ride, and operated at a sustained speed of 200 kilometers per hour (about 120 mph) - a speed which is legal in Germany. While negotiating a long right-hand sweeper, both riders felt their bikes lurch toward the center of the road. When the machines were brought to a halt (thankfully, without crashing), both rear tires had large sections of the tread rubber missing: a result of speed/heat-il1duced delamination. The tires had been installed brand-new the previous day, were properly inflated !Ind carried a V-rating: to safely sustain speeds in excess of 130 mph. Having h~r other stories about defective PireJIi motorcycle tires, Das Motorrad contacted an independent laboratory (the Technical Control Association of Munich) to run high speed tests on a batch of Pirelli, Continental and Metzeler tires. Of the group, only the MelZeler tires could sustain the speeds suggested by their speed ratings; a result that surprised eveD . the. tecbnicians 0pera1i.ng. til test equipment. . When I contacted the United States representatives of Pirelli and Continental concerning the information in the Das Motorrad article, both manufacturers claimed the testing procedure to be at fault. Both said that the curvature of the steel drum caused the tire to flex more than does a flat road surface - the flexing causing a greater heat build-up within the tire and promoting the delamination. And both said that since the test was conducted indoors, the tires lacked the flow of cooling air that would be present on a motorcycle. These complaints about the testing procedure may be fair. Of course, there isn't a roadway in the United States where velocities of over 100 mph can be sustained legally. When such speeds are furtively achieved on deserted back roads, it's seldom possible to sustain them for more than several minutes. True, street motorcycle tires are used in some forms of motorcycle road racing, where speeds are well in excess of 100 mph. But even in racing those top speeds aren't sustained. On a race track the tire has a chance to cool down between accelerating (load on rear tire) and braking (load on front tire) cycles. The fact is, the speed rating system is in place, and motorcyclists expect it to correspond to something. Modern motorcycles are capable - right off the showroom floor - of speeds of 150 mph: a figure that modern motorcycle tires should be able to withstand. Short of the Bonneville Salt Flats, there's no real-world situation where a "sustained" high speed test might be conducted in this country. Which leaves us with the rotating steel drum as the only laboratoryrepeatable way to determine motorcycle tire speed ratings. The drum test may indeed cause more flexing within the tire than a road test. So what? Let the extra flexing serve as a safety margin ... one that would be appreciated at extremely high speeds. Motorcycle tires: What needs to change. As you can see, the motorcycle tire industry, as a whole, is a nightmare of confusing figures, antiquated rating systems, and outlandish claims. Not every manufacturer is at faultin fact recently, a few have made great strides in supplyipg information to their customers. More needs to be done. Tires are vital to the safety and performance of any motorcycles. I hate to say this, but in my opinion the tire industry should either clean up its act, or the government should be encouraged to intervene and force it to do so. What should be done to clean up this mess? Surprisingly, not much. First of all, since the Department of Transportation already sets standards for all motorcycle tires offered for sale in this country, there's no reason that the DOT couldn't standardize the ETRTO speed rating system. Granted, this European rating system doesn't really relate to 55 mile-per-hour America. But dang itl If a tire is marked as suitable for a sustained 130 mph run, somebody, somewhere should specify the parameters for that claim. The DOT and the NHTSA have the legal clout to prevent the sale and distribution of any tire deemed unsuitable for use on public highways. They are in an ideal position to enforce a real istic speed rating system. Next, since folks who load their motorcycles to the absolute limit (and beyond) seldom travel at sustained speeds in excess of 100 mph, why not have a tire's maximum load capacity refer to some realisticveJocity? I would suggest 85 mph as a viable figure: abp.u.t.as. fil~~ \l Y91l <;;In go in this country without being arrested. The current system of rating maximum loads at the pie-in-sky ETRTO speeds is silly, to say the least. The tire manufacturers should begin sizing their products in accordance with the metric system. Since the inch and alpha-numeric-systems are confusing and inaccurate, hopefuJIy they'll vanish into antiquity. Certainly there's no need for three different sizing systems in one motorcycle market. There's another reason for changing to the metric sizing system. The metric designations are the only ones which describe, in plain numbers, the height and width of a tire. Shorter and wider tires are coming in the future, and the other size rating systems have no provision for describing these new profiles. For the period of time it would take for the industry to switch toan all-metric system, dealers could stock cross-reference charts ... something they have to do with the present systeml Section 119 of the Federal Motor Vehicle Safety Standard should be revised to include a subsection describing acceptable size tolerance for motorcycle tires. Since some tire sizes have an overlap of rim sizes (will fit and work on more than one rim size), the manufacturer should specify the operating width for each acceptable rim. Section 119 already mandates that the manufacturers specify what rims are applicable for each tire, so an operating width would be a natural extemion of this regulation. This would enable a tire customer to be reasonably sure that his new tire will fit his motorcycle... before that tire is mounted and installed. Last, but not least, I'd like to see the tire manufacturers list some real, understandable guidelines for recommended tire inflation. Ideally, such recommendations would be supplied in chart form for pecific motorcycles. At the very least, the tire customer should be advised of minimum tire pressure at the time ofsale. Some manufacturers (Iaudibly) offer a consumerinformation phone line to provide this information. All should do so. Since I don't [orsee any of these changes in the near future, I'd like to make a proposal. Let us, the people who ride motorcycles, share this information among ourselves. l.arge motorcycle clubs (and even small ones) could survey their membership for the results of running various brands of tires on various motorcycles. The survey should include what size of tire on what kind of motorcycle, what inflation pressures were sustained, what kind of load was placed on the motorcycle, and what kinds of speeds and riding conditions the tires were subjected to. The results of such a survey wouldn't be absolute - after all, everybody rides a bit differently. But if the data base were large enough, such a survey could provide a useful body of information. Information that the tire manufacturers won't (currently) share with their customers. In the meantime, I propose that when a fellow rider asks you about the tires on your motorcycle; tell him. Honestly. Share whether or not you check and maintain the proper tire pressures. Tell him how fast you ride, and whether or not you're into drag racing and wheelies. Describe the kinds of speeds you main rain, and the kinds of loads the tires were subjected to. And tell him - honestly· -whether or not you like the tires. Things may change. One thing's [or sure: tires will continue to improve. and the seleclion of tires will become greater yeL Hopefully, the process of selecting a new motorcycle tire will become an easier one. _