Can You Improve the Accuracy of a GPS Speedometer in a Classic Car for Reliable Speed Readings?

March 19, 2024

GPS technology has revolutionized the way we navigate. With the ability to pinpoint our location anywhere in the world, it only stands to reason that this technology would find its way into our vehicles. GPS speedometers are becoming a popular choice in classic cars for their accuracy in speed readings. But, as is true with any technology, it’s not without its flaws. The question then arises: Can you improve the accuracy of a GPS speedometer in a classic car for reliable speed readings? Let’s delve in and explore the possibilities.

Understanding the GPS Speedometer

Before we get into how to improve the accuracy of a GPS speedometer, let’s first take a step back and understand how it works. Unlike traditional speedometers, a GPS speedometer does not rely on the vehicle’s transmission, tires, or odometer. Instead, it utilizes satellite signals to determine the car’s speed and location.

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A GPS speedometer calculates speed based on the time it takes for signals to be transmitted from the vehicle to at least three satellites and back. This calculation is done multiple times per second, providing near real-time speed data. However, despite this high level of detail, GPS speedometers can occasionally give inaccurate readings due to factors such as signal interference, satellite position errors, and atmospheric conditions.

How to Improve GPS Speedometer Accuracy

Now that we have a handle on how a GPS speedometer functions, let’s explore some ways to improve its accuracy.

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Firstly, ensure that your GPS speedometer is getting a clear signal. The accuracy of your speedometer relies heavily on the quality of the signal it receives from the satellites. Obstacles such as tall buildings, dense foliage, or even certain weather conditions can interfere with the signal, leading to inaccurate speed readings.

To mitigate this, always try to position the GPS receiver in an unobstructed location where it can have a clear line of sight to the sky. Avoid installing it under metal surfaces as these can block the signal.

Another way to improve the accuracy of your GPS speedometer is by keeping it updated. Manufacturers often release firmware updates that enhance the performance of the device and rectify any known errors. By regularly updating your device, you can ensure that it is always performing at its best.

Factors that Affect GPS Speedometer Accuracy

While a GPS speedometer may be more accurate than a traditional speedometer, there are still factors that can affect its accuracy. As we’ve discussed, one of the main factors is signal interference.

Another important factor is the number of satellites the GPS receiver is connected to. The more satellites, the more accurate the speed reading. Most GPS speedometers require a minimum of three satellites to function, but for optimal accuracy, it’s best to have a connection to at least four or five.

The quality of the GPS receiver itself is also crucial. More advanced receivers can compensate for the delay caused by the atmosphere and provide more accurate speed readings.

When the GPS Speedometer is Ideal

Despite potential accuracy issues, there are still scenarios where a GPS speedometer is the ideal choice. For example, in a classic car where the original speedometer may not be functioning correctly or is completely broken, a GPS speedometer can be the perfect solution.

It may also be a good choice if you often switch between tires of different sizes, as the size of the tires can affect the accuracy of a traditional speedometer. Since a GPS speedometer does not rely on the vehicle’s tires, it will not be affected by tire size changes.

Furthermore, a GPS speedometer is also ideal if your car is modified to the point where the original speedometer no longer provides accurate readings. In such cases, a GPS speedometer can provide a more accurate and reliable speed reading.

In conclusion, while a GPS speedometer can have errors, there are ways to mitigate them and improve their accuracy. By understanding how they work and the factors that can affect their accuracy, you can ensure that you’re getting the most reliable speed readings possible.

The Influence of the Drive Cable and Output Shaft on Speed Accuracy

A traditional speedometer operates using a drive cable that is connected to the vehicle’s output shaft. The rotation of the shaft is transferred to the speed cup by the drive cable, which creates a magnetic field. This field forces the pointer needle to move across the speedometer, providing a speed reading. However, any wear or damage to these components, such as the drive cable or output shaft, can lead to inaccuracies in the speedometer reading.

In a classic car, these components may have experienced significant wear and tear over the years, making the traditional speedometer less reliable than a GPS speedometer. In contrast, a GPS speedometer does not rely on these mechanical components, but rather on satellite signals to provide the speed reading. This means that the condition of the drive cable and output shaft does not affect the gps speed.

However, one must keep in mind that even GPS speedometers can sometimes give inaccurate readings. But by understanding the factors affecting their accuracy and taking steps to mitigate them, you can improve their performance. For instance, ensuring a clear signal, keeping the device updated, and having a high-quality GPS receiver can make a significant difference in the speed accuracy.

The Role of Odometer Accuracy, Tire Size, and Cruise Control in ensuring Speed Accuracy

While the GPS speedometer offers several advantages over the traditional speedometer, it’s also important to understand the role of odometer accuracy, tire size, and cruise control in ensuring speed accuracy.

The odometer accuracy is essential in providing an accurate measure of the distance travelled, which in turn influences the speed reading. Therefore, it’s vital to ensure that the odometer is functioning correctly and is calibrated correctly to provide accurate readings.

Moreover, the size of the tires can also impact the accuracy of a traditional speedometer. If you frequently switch between tires of different sizes, the traditional speedometer may not provide accurate readings as it is calibrated for a specific tire size. However, this is not an issue with a GPS speedometer as it does not depend on the tire size.

Finally, if you often use the cruise control feature, a GPS speedometer can offer more reliable speed readings. That’s because cruise control maintains a constant speed based on the speedometer’s reading. If the speedometer is inaccurate, the cruise control will also be inaccurate. By switching to a GPS speedometer, you can ensure that the cruise control feature is based on accurate speed readings.


Given the potential inaccuracies introduced by components like the drive cable and output shaft or factors like tire size and odometer accuracy, a GPS speedometer proves to be a more reliable choice, especially for a classic car.

However, as with any technology, GPS speedometers are not without their flaws. They can sometimes give inaccurate readings due to factors like signal interference, satellite position errors, and atmospheric conditions. But by understanding these factors and taking steps to improve them, you can significantly enhance the speed accuracy of your GPS speedometer.

Ultimately, whether you opt for a traditional speedometer or a GPS speedometer, what’s most important is that you understand how they work and how to ensure their accuracy. Only then can you have a safe and enjoyable driving experience, knowing that your speed readings are reliable and accurate.