Issue link: http://pfmmag.epubxp.com/i/77229
Under inflation is the leading cause of tire failures. Tis is easy to visu- ally identify. Heavier wear on the outside tread and lighter wear on the center tread is a clear sign of under inflation. Heavier wear in the center of the tread and lighter wear on the outside is a sign of over inflation. How about a properly inflated tire with "feathered" tread blocks? Sus- pension wear, alignment issues...or extremely aggressive driving. Of course, under inflation also increases tread wear and reduces tire life. Tire performance and tire failures aside, a properly inflated tire both saves gas and delays buying replacement tires. Simply put, it lowers op- erating costs. Nitrogen Remember when filling tires with nitrogen was an interesting topic but there was no compelling reason to use it? It was new, and perhaps a gimmick. Opinions were divided. Tat was then – before Tire Pressure Monitoring Systems. Tis is now – every new police car has TPMS in every wheel. Moist, humid air attacks the TPMS, and these are expensive. If the air dryer on the air compressor is broken, fix it. If you can manage to fill the tires with nitrogen, do it. Te jury is in on nitrogen. It allows the tire to hold its proper inflation pressure much longer. It won't corrode or attack the TMPS. Valve Stem Caps? Yep, these are actually very important. Tires without valve caps lose air pressure. It is not the cap that keeps pressure in. Instead, it is the cap that keeps dust and debris out. Dust and debris get into the valve seat and allow the valve to leak, which lowers tire pressure. If it is not a constant, slow valve leak, dirt and dust in the valve seat may allow the valve to "burp" as the tire is being driven. A little air leaks as the tire hits every railroad track, every pothole, every section of rough pavement, every rib on a washboard road. Again, the result is lower tire pressure—the number one cause of tire failure. Tire Mounting Checking the tire pressure in a cross-section of the fleet is the first diag- nostic step related to tire failures. Te second step is the proper method of tire mounting. Te correct liquid lube must be used on the tire bead during installation and seating. Tis may seem like a small, picky issue, but it is directly related to the problem of under inflation. A properly lubed bead will both slip under the wheel lop and fully seat during tire mounting. Te use of dried-out lube, or no lube at all (water is not lube), may result in sections of the tire bead being torn or getting small cuts during mounting. Te result is, of course, slow leaks and under inflation. Use Only a Patch/Plug Te only proper tire repair, regardless of the puncture, is a patch / plug combo. Not a patch-only. Not a plug-only. Why not use a patch-only? After all, a patch pretty well seals the inside of the tire. Te problem is that holding air is just one aspect of a proper tire repair. Keeping mois- ture out of the belt package is the other aspect. If moisture gets into the belts, they may corrode. However, the mois- ture will certainly cause the belts to bubble, raise and separate slightly. Te resulting belt slip will cause friction, heat and finally complete belt separation and tire failure. Why not use a plug-only? A couple of reasons. First, the plug-only X Firestone's TJ Tennent explains some of the reasons the patch/plug combo is the only acceptable repair. For one, it forces a dismount and inside inspection of the tire. may not completely or entirely seal the damaged area. For example, it may seal a perfectly round hole, but not a hole that has slight tears around the puncture. Tese micro-cuts are hard to see, but they will allow air seepage. Just as importantly, tires that get a plug-only repair frequently do not get an inspection of the interior of the tire. Te number one reason for the mandate of a patch / plug combo is to force a tire dismount and a proper tire inspection. For the record, according to the Rubber Manufacturer's Association and the Tire Industry Association, a tire that has been run 20 percent under inflated has irreparable internal damage. It permanently ruins a tire to operate a police vehicle on tires inflated to 28 psi or less. You cannot pump it back up to 35 psi and think all is well. How about really small punctures? Like that from a finishing nail? Won't a patch work the best? After all, that is a very tiny hole to pull a plug through. It doesn't matter. A patch / plug combo is the only accept- able repair. Te trained tire tech may run a carbide cutter (drill bit) into the tiny puncture to allow it to accept the appropriately sized patch / plug combo. Drill out the tiny puncture hole? Make the puncture bigger, just so it can accept a patch / plug? Right. Engage the Belt Package Most people know you cannot repair a tire with a puncture in the side- wall. Some people know you cannot repair a tire with a puncture in the shoulder, i.e., the edge where the tread meets the sidewall. In general terms, the shoulder includes the outer tread blocks and extends all the way to the first groove. It is widely assumed you can make the repair as long as the puncture is on the tread, i.e., the rubber that actually meets the road. Not true! Te shoulder has a great deal of flex. www.pfmmag.com 47