Pierce Enforcer, Operator'S Manual

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Wheels and Tires / 6-41
MAINTENANCE
Wheels and Tires
6-27. Tires
6-27.1 Fire Service Rated Tires
Fire apparatus axle loads are often higher than typical vocational trucks. Tire manufacturers recognize the need for
fire apparatus to carry higher loads, but also understand that in most cases a fire apparatus does not travel at high
speeds for long periods of time. Most apparatus on a fire call travel only a short distance, and then they idle for
extended periods.
Based on this duty cycle, tire manufacturers are willing to rate some of their tires with a special “fire service”
intermittent duty rating. This allows the tire to carry greater loads or attain higher speeds. The understanding is that
these high loads and speeds will not be sustained for long periods of time.
The reason tire manufacturers are able to provide this intermittent rating is that a tire used over short distances does
not have a change to heat up. A tire's worst enemy is heat. Heat is generated by the flexing of the rubber inside the
carcass. This heat builds up over time and will degrade the rubber, eventually leading to a greater risk of tire failure.
This heat build-up happens more quickly when the tire is driven faster, or when it carries more load.
To avoid tire degradation, fire-service rated tires have limits on the amount of time they can be driven at high speed
and high load before they must cool-down.
6-27.2 Fire Service Ratings
There are two cases where intermittent fire service ratings can apply, extra load and extra speed:
•
Extra Load: In this case the tire is allowed to carry extra load, higher than the standard rating.
• Extra Speed: In this case the tire is allowed to attain higher speeds than the standard maximum speed rating.
A fire-service rated tire can carry extra load, or attain higher speeds, but not always both at the same time.
You can determine if your tires are being operated under a fire service rating by checking the maximum load rating
listed on the sidewall of the tire. Find the gross axle weight rating (GAWR) on the yellow final vehicle manufacturer
label in the cab. Divide each GAWR rating by the number of tires on that axle. If the GAWR rating divided by its tires
is greater than the sidewall rating for the tire, then your tire is operating in a fire-service condition.
6-27.3 Fire Service Rating Rules
Tires in a fire service condition must only be operated using the following rules:
6-27.3a Goodyear Fire-Service Rating Rules
After driving for 50 miles at speeds above 50 mph, stop for 20 minutes or reduce speed to 50 mph for 20 minutes
to allow the tire carcass to cool.
Never load a tire beyond its rated capacity or sudden tire failure leading to a loss of vehicle control,
property damage, personal injury, or death may result.
This vehicle may be equipped with fire-service rated tires. Tire may fail if driven continuously at
highway speeds. Keep tires properly inflated. Follow the instructions in this manual to avoid degrading
tire material. Crash caused by tire failure may injure or kill.