Maintenance: Keeping treadworthy
| October 05, 2008 |
Tires can claim a big chunk of your maintenance and repair budget. Here are some ways to make your off-the-road tires last longer and prepare them for a retread afterlife.
With a few exceptions, the tire shortage experienced in 2005-2006 is easing, says Mike Berra, vice president of Community Tire Retreading. But as the costs of base tire materials such as oil and steel fluctuate, the price of tires is still trending upwards. Retreading your OTR tires stretches their service life, extends the time between buying new replacement tires and decreases used tire recycling/disposal fees.
To get the most wear out of these tires, contractors are putting in place pro-active tire maintenance programs that squeeze the most service out of new tires while maintaining the integrity of the tire casings so they are good candidates for future retreading. Treadability is a result of good operating practices, consistent maintenance and proper repairs.
Maximizing treadability during daily operations
The calendar age of your tires has less to do with their service life than how well you maintain them. Putting a new tire into service with poor maintenance will age it before its estimated mileage or hour rating. According to industry data cited by Tim Good, OTR global customer accounts manager at Goodyear, only 7 percent of OTR tires are truly worn out when they’re removed from service. Tread and sidewall cuts and impacts account for 74 percent of the removals.
Good says monitoring and maintaining work terrain and access roads conditions throughout the day, especially in quarry and mining applications where rock is hauled, is important because sharp rocks and debris will wedge into the tire, resulting in an out of service tire that may not be suitable for retreading. Ideally, haul roads should be clean, dry, with few undulations or hazards. Graders should clear roads often during each shift because running a tire on ruts can cut the tire’s sidewall and stress the carcass.
When conditions are wet, your tires are more vulnerable to damage. “Water acts as a lubricant on tires and will let rocks cut through the rubber like butter,” Good says. If your tires start to spin on a wet ramp, Good says it’s like spinning over knives.
Keep tires clean. “If there are stones between the lugs, they will keep drilling down until they create a cut separation,” Good says. “Tires can inhale rocks.”
Match the right tire to the job. Berra says the fatigue factor will set in much faster if you exceed the tire’s ton/mile rating. “You will tax the tire beyond what it is meant to do,” he says. “This causes heat, which is the enemy of all tires.”
Monitor user abuse. Operators who drive too fast, run too heavy or keep their vehicle’s tires too soft will prematurely age the tires and make them unsuitable for retreading.
Proper inflation pressure is the single most important feature of a good tire maintenance program. In terms of retreadability, Goodyear says running 30 percent underinflated drains 30 percent of the life out of a good radial casing.
Proper inflation pressure is dependent upon the load or overload, the kind of job application, tire type and its location on vehicle. In general, when overloads are encountered the inflation pressure should be increased 2 percent for each 1 percent of overload to a max of 14 percent or 7 percent overload, according to Goodyear.
Running an underinflated tire will cause it to flex more than it is designed to,creating heat which weakens the casing. The Tire Retread and Repair Information Bureau says hot tires suck up puncturing objects.
Over-inflation, as measured when the tire is cold, also leads to severe cutting and chipping, especially on wet surfaces.
Don Chambers, product manager for tire and wheel assembly manufacturer OTR Engineering, says improper inflation also leads to wheel problems. If the vehicle is overloaded, some wheels can crack which will lead to tire failure. Chambers says it is important to respect the tire’s load and speed ratings, even if it means the operator may have a rougher ride.
The Rubber Manufacturers Association recommends that tires found to be underinflated by 20 percent or more should be immediately removed from service, dismounted and inspected for damage.
Maintenance and repair
If you and your tire dealer track the lifecycle costs of your tires with a computerized tire management program such as Bridgestone Firestone’s TreadStat, you can pull reports on each tire’s usage, maintenance and repair history. Some software will forecast future use and estimate retread times. Encourage your operators to also record any other observations they have into the tire program. Have them check for irregular tread wear and previous repairs. The data they store will be useful for future repairs and retreading.
Inflation gauges should be recalibrated daily. Standardize specific inflation pressures for your fleet. A consistent baseline pressure reading makes it easier to spot an inflation problem. Set tire pressures cold – the air in the tire should be the same as the outdoor air temperature. Before measuring and adjusting tire inflation pressures allow tires to cool 3 to 4 hours, and drive the vehicle less than one mile. Set tire pressure for the loaded condition.
Bandag says correct repairs will preserve a good casing and recommends repairs be done by a technician certified by the Tire Industry Association. The Tire Retread and Repair Information Bureau (TRIB) adds tire repairs must be made with the tire dismounted from the wheel so that repairs are made on the inside of the tire. Repairs made on-the-wheel don’t check rim or wheel damage, both prime locations for a failure.
The RMA advises a tire’s injury should be filled with a rubber stem or suitable alternative and vulcanized to the inside of the tire. Rubber stems contain special bonding gum that reacts to the vulcanizing cement to create a molecular bond with the tire. Michelin says to avoid lifting tires through the center with a crane hook or other devices, because this can damage the critical bead area. Instead, lift the tire under the tread by using flat straps. Flat straps are recommended over steel slings or chains because they will not cause cuts or abrasions.
How much rubber does a retread need?
When you pull a tire to be retreaded will vary depending on its repair history and where the tire has been used. Berra says tires that run on rough haul roads need to have about 25 percent of their rubber to make them retreadable. Tires that run on smooth roads can be pulled when they have 10 to 15 percent of their rubber left. Vehicles such as dump trucks that run on public roads have different requirements and DOT regulations, so it is important to work with your tire dealer to evaluate when those tires should be pulled.
Tire manufacturers recognize their customers need to lower their cost per hour of operation while still running reliable tires in heavy terrain conditions. Mike Poirier, North American sales manager for Bridgestone Bandag Tire Solutions, says the cost of retreading can save up to 50 percent of the cost of a new tire. In field tests of BBTS Continuum C1073 retread tire, designed for rigid dump trucks and haul applications, the retread tire gets 82 percent of the hours a new tire provides at 60 percent of the cost. The Continuum C1072, designed for loaders, dozers and graders, emulates the Bridgestone VMT tire and matches new tire tread depth, allowing contractors to mate retreads and new tires of similar designs.
Designs such as the new Bridgestone M775 on/off-highway radial tire’s stone rejector platforms and all-steel casings lengthen a tire’s service life by resisting cuts and punctures, improving its retreadability.
Firestone’s FD835 on/off-highway tires are an example of heavy, 1-inch-deep treads with split-belt construction that helps the casing resist cuts and punctures by enveloping debris, reducing belt damage and increasing treadability.
Goodyear Tire and Rubber
Tire Retread Information Bureau
OTR Wheel Engineering
Community Tire Retreading
Rubber Manufacturers Association
Tire Industry Association
To download a PDF of Bandag’s retread process, click on www.bandag.com/TireProducts/RetreadProcess.aspx.