Courtesy US department of Transportation
Commercial Motor Vehicle Tire Maintenance Practices
The following summarizes the key observations and conclusions about tire inflation condition and maintenance practices of commercial motor vehicles as observed from the sample tire pressure data collected:
· Approximately 7.08% of all tires are underinflated by 20 psi or more. Only 44.15% of all tires are within ±5 psi of their target pressure.
· For-hire carriers' (truckload (TL), less-than truckload (LTL), and owner-operators) vehicles generally reflected better tire inflation maintenance practices than private carriers' vehicles. As a group, for-hire carriers sampled had 7.01% of all tractor tires underinflated by 20 psi or more. In contrast, the private carriers sampled had 13.21% of all tractor tires underinflated by 20 psi or more.
· Tire inflation maintenance practices correlate closely with the size of the fleet. For tractors, fleets with 50 power units or less have 19.07% of their tires underinflated by 20 psi or more, while fleets of greater than 3,000 power units have only 2.06% of their tires underinflated by 20 psi or more. Similarly, motorcoach fleets with less than 50 power units have 11.75% of their tires underinflated by 20 psi or more, while fleets with over 500 power units have only 2.09% of their tires underinflated by 20 psi or more.
· Transit bus operators have better tire pressure maintenance than chartered motorcoach operators based on the sample data. Only 3.09% of transit bus tires are underinflated by 20 psi or more, while 9.37% of chartered motorcoach tires are underinflated by 20 psi or more. Additionally, 49.88% of transit bus tires are within ±5 psi of target (a very high percentage), compared with only 34.22% of chartered motorcoach tires.
· Tractors and trailers have a significant challenge with mismatched dual tires. Approximately 20% of all tractor dual tire assemblies have tires that differ in pressure by more than 5 psi. One out of four trailer dual assemblies (25%) have tires that differ in pressure by more than 5 psi.
Economic Analyses of Tire Pressure Monitoring & Inflation Systems
The following table shows the economic consequences of tire pressure monitors and the costs which tire pressure monitors may be able to reduce.
Economic consequences of incorrect inflation pressures
Tire pressure monitors may be able to reduce
· Increased tire wear
· Reduced tire life
· Reduced fuel economy
· Road calls
· System procurement costs
· System maintenance costs
· Total direct costs avoided with properly maintained tires
· Tire installation costs and associated downtime
· Costs from improved safety
Key observations from the cost-benefit analyses are as follows:
· Tire-related costs are the single largest maintenance cost item for commercial vehicle fleet operators. Nationwide, the average tire-related costs per tractor-trailer are about 1.9 cents per mile, or about $2,375 for a 125,000 annual mileage operation.
· For the average fleet operator in the United States, improper tire inflation increases the annual procurement costs for both new and retreaded tires by about 10% to 13%.
· Fuel economy loss due to improper tire inflation is about 0.6% for typical TL and LTL operations.
· Improper tire inflation is likely responsible for about one roadcall per year per tractor-trailer combination due to weakened and worn tires.
· For a typical TL or LTL operator, improper tire inflation increases the total operating costs by about $750 annually per tractor-trailer combination. Cost penalties for other types of fleets are similar and range from about $600 to $800.
· One of the primary motivators for fleets to purchase automatic tire maintenance systems is that operators will not have to spend as much time checking tires for proper inflation. An average 18-wheel tractor-trailer could easily take 30 minutes to check the pressure of each tire and add air to two or three of the tires. Most fleet maintenance departments ask operators to check tire pressures weekly. However, if operators only check tires twice a month, the total annual labor would be approximately 12 hours (0.5 hours/inspection × 24 inspections). At $25/hour, the cost would total $300 annually in tire inspection costs. This is likely a conservative estimate of tire pressure maintenance costs.
· The cost associated with routine tire pressure maintenance, combined with the increased costs due to poor inflation, arguably represents the total costs that could be addressed (that is, reduced) by tire pressure monitoring and automatic inflation systems.
· There are numerous tire pressure monitoring and automatic inflation systems available from vendors that are specifically tailored to commercial vehicles. If such systems could be installed for approximately $1,000 per tractor-trailer combination, and if they were effective in mitigating incidences of improper tire inflation, such systems would indeed be highly costeffective. Return-on-investment periods even for an average fleet would be between 1 and 2 years.
· Sensitivity analyses show that even for fleets with relatively "good" tire maintenance practices (fleets which would demonstrate a 25% reduction in total cost of improper inflation compared to "average"), the cost-effectiveness of tire monitoring and automatic inflation systems is still within return periods of less than 3 years.
· Tire pressure monitoring and automatic inflation systems become even more cost-effective, if safety-related benefits are explicitly considered. However, direct costs associated with a fleet's safety record (such as injury claims, insurance premiums, workers' compensation claims, as well as "goodwill" with customers and suppliers) are difficult to estimate, and even more difficult to determine what portion could be attributed to poor tire pressure maintenance. Therefore, while improved tire pressure maintenance will have an important and direct impact on reducing commercial motor vehicle-related property damage, injuries, and fatalities, the economic benefits of such safety improvements have not been quantified.
· Tire pressure monitoring and automatic inflation systems have not achieved significant market penetration rates. Hindrances to increased usage appear to focus on fleet operators' concerns over system reliability and required maintenance costs, as well as the initial costs of the systems.
The analyses presented in the report strongly suggest that the savings potential from tire pressure monitoring and automatic inflation systems could support the purchase prices of systems and products currently in the marketplace. The challenge for the supplier community is to prove reliability and reduce or eliminate added maintenance for the systems themselves