# How accurate are motorcycle speedometers?

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On testbikes we typically see an error of a few percent in the speedometer reading—at times up to 10 percent and always on the high side. … According to this law, a speedometer can read high by as much as 10 percent plus 4 km/h at a specified test speed, but under no circumstances can the speedometer read low.

## How much is a motorcycle speedometer off by?

Most speedometers I have checked lately are about 3–5% high.

## How far off are speedometers?

Your speedometer reading must be within a range of plus or minus four percent off, but that’s four percent over the entire range of the speedometer, and that range can then be shifted in what’s called a bias. Look at the above chart based on a Scion’s technical guide.

## How accurate are speedometers?

“The accuracy of the speedometer in most vehicles, including Volkswagens, is generally within a few percentage points of actual speed,” Tetzlaff says. “Odometer readings are designed to be quite accurate.” Why is there a built-in factor of error for speedometers? Speed is a measure of distance over time.

## How do I know if my speedometer is accurate?

If the speedometer reading is higher than the actual speed, the speedometer is fast. If the speedometer reading is lower than the actual speed, the speedometer is slow – this is what you should end up with.

## Why are speedometers inaccurate?

Because that measurement changes continuously, as the tire expands and contracts with use and environment, your speedometer is never accurate. Circumference is a simple function of a tire’s radius, or the distance between the center of the wheel and ground.

## What is the margin of error for speedometers?

Most new speedometers are believed to function with a 5% margin of error. … Police speedometers are sometimes calibrated on a rolling road at regular intervals to ensure their accuracy.

## Is GPS or speedometer more accurate?

Speedometers are not allowed to read lower than the actual speed of the car, but they are permitted to indicate a value that is 10% higher than the actual speed, plus 4. GPS, on the other hand, uses a purely mathematical technique to measure the speed of the vehicle and is therefore more accurate than a speedometer.

## Can your speedometer be wrong?

Speedometers can show the wrong speed

There are several factors that can cause a speedometer to show a speed that is incorrect. One major factor is the age of the car, as many times older vehicles with a lot of miles and wear on them will have speedometers that are not as exact as they used to be.

## Are you allowed 10 percent over the speed limit?

Most motorists, when discussing speeding, will have no doubt heard tales of the “10% plus 2” rule. … The ‘rule’ itself is quite straightforward: if the speed limit is (for example) 30mph, the rule states that you won’t get a speeding ticket unless you are going 10% plus 2 mph faster than the limit.

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## How much does it cost to have a speedometer calibrated?

Getting a Speedometer Calibrated

Most auto-mechanics perform speedometer calibrations, and some driving schools perform them as well. The cost is usually approximately \$75.

## What causes the speedometer to fluctuate?

While you are driving, if you notice the needle on the speedometer jumps erratically from one number to another, the speedometer cable is most likely damaged or the sensors on the driveshaft are not accurately sending the signal through the cable. … If this occurs, the entire cable and housing needs to be replaced.

## How accurate are speedometers UK?

Under UK law – which is based on a European Union standard – speedometers must never underreport a vehicle’s speed, while it must never overreport by more than 110% of the actual speed + 6.25mph. So if you’re going 40mph, your speedometer may read up to 50.25mph – but it can never read less than 40mph.

## Is a GPS speedometer legal?

Under the law a GPS system, even if it gives an indication of speed, can’t be regarded as fulfilling the legal requirements. So to answer your question a GPS speedo isn’t legal.