How does tire pressure affect mileage accuracy?


Tires that are slightly under-inflated might seem like a trivial matter and, over short distances, they generally are. But change the distance or the number of fleet vehicles with tires that haven’t been inflated to the correct pressure and the effect is significant. And it’s hurting more than just your fuel economy.

Something that’s important to a lot of commercial fleets is recording mileage – it might be used in a range of situations including:

  • Determining next vehicle service
  • Replacement of vehicle parts such as tires or oil filters
  • Off road tax credits
  • Calculating fuel economy
  • Warranty claims
  • Route optimization

It’s important then that fleets can rely on accurate mileage reports for their vehicles. So how can incorrectly inflated tires affect the vehicle’s instrument accuracy, and how can you make sure this doesn’t affect your fleet?

Changing tire pressure changes instrument readings

Let’s just reiterate that tire pressure won’t have a big impact on instrument readings, but when any slight variation is extrapolated over a large number of fleet vehicles then the discrepancy can be significant enough to warrant your attention.

So how does incorrect inflation affect the vehicle’s instrument readings?

In most vehicles, speed and distance readings are based on the number of axle revolutions rather than turns of the wheel. Instruments use the standard diameter of the wheel to calculate how much distance has been covered, and base odometer and speedometer readings on that. But overinflating or underinflating the tire changes the diameter, slightly skewing the calculations. For example, an overinflated tire has a larger diameter and thus covers a greater distance with each axle turn. The result is that the odometer under-reports the actual distance covered, and the speed will also be less than what it normally would be.

Solving the tire pressure problem

While the mechanical instruments in a vehicle can be affected by the wrong tire pressure, there is something that isn’t. Intelligent fleet management systems that use GPS tracking maintain accuracy regardless of the vehicle’s tire pressure. Customers using Telogis have verified its accuracy for both mileage and vehicle engine hours, providing a much more reliable method of tracking vehicle metrics.

Five more reasons to avoid incorrect tire pressure

While we’re talking about tires with the wrong PSI reading, here are a number of other reasons to keep tires at the correct pressure.

  1. Accidents – Studies indicate that underinflated tires are a contributing factor in more than 20% of accidents.
  2. Overheating – Underinflated tires are more prone to overheating, which can lead to other problems.
  3. Blowouts – There is a greater risk of the tire suffering a blowout due to more exposure against sharp road edges.
  4. Uneven tire wear – Both underinflated or overinflated tires create an abnormal contact pattern on the road, causing uneven tire wear, either on the edge of the tire wall or along the center line.
  5. Fuel economy – Underinflated tires can reduce a vehicle’s fuel efficiency.

So even though your fleet management software is keeping accurate speed and mileage records, there is still good reason to keep tires properly inflated. Telogis Fleet can help you do that working with tire pressure monitoring systems to alert you whenever vehicles are not inflated to the recommended pressure rating.

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