There are many important systems that work harmoniously on your apparatus to provide reliable, safe, and effective operation but safety and reliability starts at the ground and works its way to the operator’s seat. The first point of contact for your apparatus and the roadway is the tire, one of the many underestimated items that play an important role in the handling characteristics of your vehicle. Tires provide not only the means by which to grip the roadway and propel your vehicle down the road, but have the responsibility to resist breaking traction when bringing the vehicle to a stop. Providing support and ground contact when cornering is equally important. Your tires are also the first component of the vehicle’s suspension system absorbing a large amount of jounce and rebound. With all of the above taken into consideration, inspection, maintenance, and preventive replacement of tires should be considered a high priority in any agency.
Maximizing tire life is important to any operation; Goodyear states, “The driving habits that cause the greatest tire wear are cornering, aggressive starting, and hard braking. Riding the brake swerving back and forth will also expedite wear.” That isn’t easy for us to fix, the excerpt above just described almost every run our vehicles experience. Although training can “curb” some habits like riding the brakes and teach other techniques of braking and accelerating, most of these items that effect tire wear by driver input will be unavoidable for us. This is where frequent inspection is necessary to catch any issue created by driving under these conditions. Tires should be visually inspected for bulges, bumps, abrasions, and defect in workmanship. There should be no evidence of damage to the sidewalls, exposed cords, missing pieces of tread, or unusual wear. If unusual wear is discovered it should be reported and evaluated by a mechanic to determine if suspension problems, loading, balance, or other issues could be the root cause. Dual tires should be inspected to insure that they are not rubbing together, are matched, and are free of rocks or other road debris that could have become lodged between them.
Tire inflation is another important factor in the performance and life of you tires, it is commonly seen that tires are inflated to the maximum pressure listed on the tire, however, this is not always the recommended practice. For most vehicles, the proper tire pressure was determined by the vehicle manufacturer and listed on the B pillar of the vehicle. Tire manufacturers state to follow these pressure guidelines and not the maximum tire pressure listed on the tire. For fire department apparatus, weighing the vehicle annually as mentioned in our previous article and custom tailoring the tire pressure for the in-service weight proves to be an effective means to find a safe and efficient tire pressure. There are load tables available from the Tire and Rim association that list the tire size, model, configuration, and load on the tires to formulate a safe tire pressure that maximizes performance, ride, and wear. You can also contact your tire installer for a copy of the information relating to the tires on your vehicle. Once tire pressures are set meeting the tire manufacturer’s specification, the load chart recommendations, and the approval of the vehicle manufacturer, the sticker can be updated. When inflating tires, it is important to inflate to your desired pressure when the tire is cold. As a vehicle is driven, heat causes the tire pressure to increase, adding air when the tire is warm will result in under inflation once the tire cools to ambient temperature. With ambient temperature in mind it is important to note that extreme or seasonal changes in temperature will also effect tire pressure. Goodyear provides a few tips on their website and states, “Driving with an underinflated or overloaded tire causes the tire to develop excessive heat….leading to vehicle damage and/or personal injury.” On the next alarm try an experiment, touch your rear tire sidewall and the front tire sidewall as you enter the vehicle, touch again when you’re getting your equipment out for the call, compare again after the incident, and one last time when you return to quarters. Overall you would notice that the trip to the scene will produce more heat than the return to quarters. Keep in mind that what you feel now is the
temperature developed with normal pressures and driving techniques, imagine what could happen with
an underinflated tire.
Another consideration in your tire inspection is the age of the tire. Chemicals are added to tires
to allow rubber to become more flexible and as tires age the air moves through them and the chemical
weakens allowing the rubber to lose its strength and become more brittle. Tires will start to show
“weather checking” and cracks on the sidewalls or in between the tread lugs. These cracks should be
taken seriously as a sign of impending failure and the vehicle taken out of service. NFPA 1911, section
7.3 recommends that tires be replaced every 7 years or more frequently when the tread wear exceeds
state or federal standards. Tires are all stamped with a Department of Transportation (DOT) number
that will indicate the week and year of manufacture. DOT serial numbers have 12 digit and 11 digit
numbers and can be decoded with the following chart found at www.goodyear.com:
- 12-digit number: 2000’s production
- 11-digit number: 1990’s production
- M6MJEH0R0911
- M6: Mfgr Plant Code
- MJ: Government Size and Ply Code
- EHOR: Manufacturer Construction Code
- 0911: Tire Build Date (9th week of 2011)
State law specifies that tread depth on any steering tire have a minimum depth of 4/32” and all
other tires have a minimum of 2/32”. Tread depth can have a serious effect on handling and is most
noticeable during heavy rain fall or driving on slippery and muddy surfaces. Skidding is more likely on
slippery surfaces with excessively worn tires and can result in loss of control of the vehicle. Tire
manufacturers recommend routine rotation based on vehicle manufacturer guidelines or at a maximum
of 6000 miles to increase service life, this can increase the life by wearing the tread more evenly than if a
tire was left in one position.
With so much counting on the quality and condition of our tires, we must be diligent in our
inspection and reporting of unsafe conditions. As mentioned in previous articles, routine inspection and
a successful maintenance program starts with the front line operators of the vehicle(s), without these
inspections, thousands of miles may pass before scheduled maintenance could spot an issue. Together
we can keep our crews and others on the road safe.
By: Justin Claiborn
Board Member - WFC Fire Mechanics Section