Auto Hauler Tire Failure Due to Improper Operation and
Maintenance
Constellation
Heritage
> 4700 Models

4800 Models
> 4900 Models
5700 Models

5900 Models
6900 Models

40-02
Western Star
Service Bulletin

General Information
Owners and operators must understand the interdependency between tire load, inflation pressure, speed, and
temperature in order to prevent tire failures on auto haulers. Reports of recent steer axle tire failures have
shown that the front tires on auto haulers are potentially being overloaded, incorrectly inflated, and/or operated
at speeds in excess of the tire rating. If a tire is underinflated, the load that it can carry is reduced. Speed also
plays a similar role in regard to tire pressure. Many tire failures on auto haulers are caused by failure to
maintain the correct tire inflation pressure, not following correct loading procedures, and/or operating the truck
faster than permitted by the tire manufacturer. Driver’s must be aware of:
• maximum tire weight rating—under certain conditions, the maximum load may be less than what is
indicated on the sidewall of the tire;
• maximum tire inflation pressure—depending on the rim, the maximum inflation pressure for the tire/rim
combination may be less than what is indicated on the sidewall of the tire;
• maximum tire speed rating—maximum tire speed ratings may depend on the actual gross axle load of a
loaded auto hauler;
• the interdependency of tire load, inflation pressure, and vehicle speed.
For more information about specific tire brands, see the following manufacturer websites:
• www.michelintruck.com
• www.goodyeartrucktires.com
• www.continental-truck.com/www/transport_us_en/

DANGER
Overloading, improper inflation, and/or exceeding the speed rating of tires are dangerous operating
practices and may lead to sudden tire failure without prior warning. Failure to avoid these operating
practices could lead to property damage, severe personal injury, or death.
To prevent overloading of the steer tires, proper positioning and adhering to the specified weight limit is
required. Auto hauler configurations vary; contact the manufacturer of the auto hauler body for proper vehicle
loading instructions.
Tire inflation pressure must be checked regularly to ensure that the vehicle is operating with the desired
pressure. The load carrying capacity of the tires decreases dramatically with even a small decrease in tire
inflation pressure.

NOTICE
Setting the speed limiter may help the driver maintain a given speed, but in no way guarantees that the
vehicle will never exceed that speed. Driver awareness is required to limit the vehicle speed to within
safe limits.
Tire speed limits may vary depending on the load and how the load is distributed on the vehicle. Ensure the
speed limit for the tire and load combination is adhered to. To help manage the optimal speed of the truck,
Daimler Trucks North America (DTNA) will adjust the vehicle speed limiter free of charge.
Centering the vehicle on the auto hauler over the truck cab is very important. Crowding the car to one side or
the other can change the load on the steer tires considerably. It is possible that the overall load on the steer
tires is within the permissible limit, but one tire may still be overloaded. See Fig. 1 for an example of a properly
loaded vehicle.

Western Star Service Bulletin, September 2015

Page 1

40-02
Western Star
Service Bulletin

Auto Hauler Tire Failure Due to Improper Operation and
Maintenance
Constellation
Heritage
> 4700 Models

4800 Models
> 4900 Models
5700 Models

08/11/2015

5900 Models
6900 Models

f400384

Fig. 1, Centering the Vehicle Over the Cab

When the trailer is loaded, it pulls weight off the steer axle and tires because the weight of the trailer load is
behind the drive axles. See Fig. 2. Conversely, if the weight is removed from the trailer, additional weight may
be transferred to the steer axle, and the remaining load may need to be readjusted to ensure the front axle and
tires are not overloaded.

B

A

08/20/2015

f400385a

A. When the trailer is loaded its weight is distributed behind the drive axles.
B. The loaded trailer lifts weight off the steer axle and tires.
Fig. 2, The Effect of Adding Weight on the Car Hauler

NOTICE
Unloading the auto hauler trailer and leaving a single vehicle over the cab may overload the steer axle
and damage the tires. See Fig. 3.

Page 2

Western Star Service Bulletin, September 2015

Auto Hauler Tire Failure Due to Improper Operation and
Maintenance
Constellation
Heritage
> 4700 Models

4800 Models
> 4900 Models
5700 Models

5900 Models
6900 Models

40-02
Western Star
Service Bulletin

If the auto hauler will be partially unloaded at one location and the truck is driven to another location for final
unloading, the load needs to be readjusted to ensure the steer axle and tires are not overloaded; if a single
vehicle on the auto hauler is loaded over the cab with the remaining positions of the auto hauler empty, there is
a high potential of overloading the front axle.

08/14/2015

f400386

Fig. 3, Improperly Hauling a Single Vehicle

An example list of tire operating parameters is shown in Fig. 4. See Table 1 for a blank list to fill in with data
that applies to your vehicle.

Western Star Service Bulletin, September 2015

Page 3

Auto Hauler Tire Failure Due to Improper Operation and
Maintenance

40-02
Western Star
Service Bulletin

Constellation
Heritage
> 4700 Models

4800 Models
> 4900 Models
5700 Models

5900 Models
6900 Models

Example Tire Checklist
Tire Parameters

Data
295/60R225

Tire Size
For Maximum Loading:

14,780 lb

E

Tire weight rating
At what ination pressure

130 lb

At what speed

PL

65 mph

At what rim size
For Maximum Speed:
Tire weight rating

At what speed
At what rim size

M

At what ination pressure

9.00
14,320 lb
130 lb
75 mph
9.00

For Reduced Ination Pressure:

A

Tire weight rating

At what ination pressure

At what speed

EX

At what rim size

14,320 lb
125 lb
65 mph
9.00

For Rim Change:
Tire weight rating

At what ination pressure

At what speed

At what rim size

12,350 lb
120 lb
75 mph
8.25

08/21/2015

f400387

Fig. 4, Example Tire Checklist

Tire Checklist
Tire Parameters
Tire Size
For Maximum Loading:

Page 4

Data
__________

Tire weight rating

__________

At what inflation pressure

__________

At what speed

__________

At what rim size

__________

Western Star Service Bulletin, September 2015

Auto Hauler Tire Failure Due to Improper Operation and
Maintenance
Constellation
Heritage
> 4700 Models

4800 Models
> 4900 Models
5700 Models

40-02
Western Star
Service Bulletin

5900 Models
6900 Models

Tire Checklist
Tire Parameters

Data

For Maximum Speed:
Tire weight rating

__________

At what inflation pressure

__________

At what speed

__________

At what rim size
For Reduced Inflation Pressure:

__________

Tire weight rating

__________

At what inflation pressure

__________

At what speed

__________

At what rim size
For Rim Change:

__________

Tire weight rating

__________

At what inflation pressure

__________

At what speed

__________

At what rim size

__________
Table 1, Tire Checklist

Warranty
This is an informational bulletin only; warranty does not apply.

Western Star Service Bulletin, September 2015

Page 5