Support Thread for the TND 500, TND 700 or future Rand McNally products. (part two)

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How does tire pressure affect mileage accuracy?
31 Mar 2012 Jason 0 Comments

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.

 

A-GPS – What does it mean?
28 Apr 2012 Jason 0 Comments


If you’ve been browsing GPS devices you might have seen some of them, particularly GPS-enabled smartphones, boasting A-GPS. What is A-GPS? What are the benefits of Assisted GPS, and why is it a good feature to have?

A-GPS, which stands for Assisted GPS (what is GPS?), helps a standalone GPS unit to lock on to a satellite signal. Known as the TTFF (time-to-first-fix), this startup period can be challenging for GPS units where the satellite signal is weak or distorted by surrounding buildings.


It’s important to note that AGPS will only work if the device has a GPRS (data) connection, normally using a 3G connection.

How Assisted GPS helps speed things up
The first time a device attempts to lock on to a GPS satellite signal (known as a ‘cold start’) it has to download three sets of data (GPS satellite signals, almanac data, and ephemeris data) to calculate its position. A device may do a cold start if it has been switched off for a long period of time, has moved a considerable distance or the cache reset.

For standalone GPS, a cold start can take up to 12 minutes. If the signal is interrupted during that initial startup (due to a weak signal, conditions in the atmosphere, walls or trees) then it has to restart, further delaying the TTFF.

Assisted GPS can help avoid this, solving the data connection issue by linking to a web-based internet server (known as an assistance server) that already holds the current satellite information. This information is relayed to the device using GPRS (cellphone data connection service) rather than using the much slower, and possibly unreliable, radio signal from the satellite.

Even for devices doing a warm start, studies showed that using AGPS saved, on average, at least a minute.

What A-GPS won’t do
While helpful, there are some things Assisted GPS can’t do, no matter how much you want to believe it can. It doesn’t possess some magical ability to lock on to a satellite signal through everday obstructions. GPS won’t work underground, inside a building (away from glass windows) or underwater, and will be affected by dense tree cover.

AGPS won’t change that. As the name suggests it is Assisted-GPS – if you don’t have the GPS part of A-GPS then it just won’t work. All that AGPS does is significantly improve the startup time when first locating your position.

A-GPS is not to be confused with WiFi positioning or cellphone tower triangulation, methods where position can be determined when GPS is unavailable.

Some devices will use a combination of these methods to determine your position, using what is known as hybrid-positioning systems.

Integrated systems the way forward
Under ideal conditions GPS (or more correctly GNSS) is the best (fastest, most accurate) method to determine your location. However, there are several situations where GPS signals don’t work (underground, underwater, inside buildings or poor atmospheric conditions) so the future of device positioning lies in providing users with an integrated approach.

As discussed at the FIG Congress in 2010, the holy grail of device location is ‘ubiquitous positioning’ or for devices to be constantly location-aware. The only way, it appears, to achieve this is by using several different technologies to converge – GPS, WiFi positioning and cell tower triangulation.

Combining the advantages of different location technology will allow devices to automatically switch based on current conditions without requiring the user to interfere. With growing interest in location intelligence it won’t just be commercial fleet management systems that will benefit from accurate and reliable positioning systems.

 

Yes and you should be on version 4.5.3593.

Thanks,
Mark

 

I just finished 3 days of testing the issue of no roads after an update, so I will be able to test this now.

Thanks,
Mark

 

If you are on the x20 model and the SD Card you are using for the maps says Ultra or Ultra Plus please let me know.

Thanks,
Mark

 

I will test anyway.

Thanks,
Mark

 

Night/Day speeds limits are not defined in the Map DB. They define only one speed limit and that is usually for the Daytime.

I will look at the other two.

Thanks,
Mark