- Car and Driver Magazine. I don't doubt that these drivers were telling me the truth. then use the Gear Ratio calculator, it's probably a little more accurate. But the accuracy of a speedometer depends on the wheels remaining the same diameter as they were when they rolled off the production line. Thank you John D. Wilson . Aftermarket speedos? Businesses know that proximity makes a difference, and that’s why some, like Netflix, use a content delivery network to bring the data closer to you. Speedometer gear has twenty teeth. . So, gathering a fat mug of coffee for a late-night adventure (which became wee morning hours), I mapped out the plan of My speedometer is dead! If you like to travel at 10 over because the cops don't stop anyone for 10 over, you are easily risking being 20 or more over without knowing it. New ADR 18 says speedos cannot indicate less that the true speed, and over-indication accuracy is limited to a maximum 10 per cent plus 4km/h. At 70mph the difference between the two can be as much as 5mph. https://haynes.com/en-us/tips-tutorials/how-check-your-speedometer-accuracy Installing larger rims and tires corrected the builtin error. Ok so I drive a 2006 Pontiac Grand Prix. https://haynes.com/en-gb/tips-tutorials/how-check-your-speedometer-accuracy I had read on a forum dedicated to that particular make of truck the speedometers usually read 5-7 kilometres slower that the actual speed. Is my speedometer accurate? This app is known to be the best one among all the speedometer apps for iOS. These numbers are the number of revolutions the speedometer cable must turn in one mile of travel. You may now plug this figure into the following equation: Actual MPH = 60 / minutes x number of miles traveled. 0.2 miles; and my cellphone has a handy stopwatch built in (as most do). You could use a GPS device or get an app for your phone that will measure distance over time. They regulate many things about how our vehicles are constructed and how their systems must function. - Asked by car owners everywhere. In older cars a break in the cable that connects the transmission to the speedometer is the most common cause. One of the biggest signs your speedometer sensor is not working properly is the speedometer will display inaccurate readings or the needle or digital numbers will not move at all on the speedometer display. While it is possible to do this yourself, it might be a good idea to enlist an assistant so you can drive without distractions. She said she was going about 5 MPH and the speedometer was reading 80. Nissan did nothing to assist my position, my view was they hid behind the ADR. You can use nearly any freeway, or limited access expressway, or even a less traveled state or county road. If the speedometer reading is lower than the actual speed, the speedometer is slow. Whether you have a digital or manual speedometer, if it's not displaying accurate information, it doesn't really help you. The new Sky Drive uses GPS Satellite signals to operate your electronic speedometer. This means that at a true speed of 100 kilometres per hour the speedo can’t be displaying 99, or under, but it could be displaying up to 114. Question: What would be more accurate, my vehicle’s speedometer or a GPS I have on my dashboard? How to change your car’s engine oil and filter, How to clean salt and grime off the car after winter, Haynes shows you how on YouTube: Nissan Pathfinder, How to save money on car maintenance when you’re a student, 21 Nissan Versa videos added to the Haynes YouTube channel. Remember, if you wind up with, say, 5 minutes and 15 seconds for a 5-mile stretch, you’ll need to convert the seconds portion into equivalent minutes by dividing by 60. Divide your measured average speed by the speed your speedometer was showing in mph throughout the measurement. BC, via email. This could be due to two reasons. Doing the calculations using the above equation: We can see that the car’s speedometer is reading a little slow, but since it is off by just over 2 mph it’s probably nothing to worry about. But Is My Speedometer Working Correctly? Q&A - Definition of Obstructed Lane Needed. No need for ECU convertors or pulse signal generators screwed onto your transmission. Speedometer Check (in MPH) Orig Tire Dia. 2. Which is more accurate, the speed shown on a speedometer or a sat nav? Image credit: Pixabay. Is there some way I can check either my speed or the officer's … If the final number is 1.0 congratulations, your speedometer is accurate. Often, the best way to do this is to have your speedometer calibrated by a qualified professional, followed by a certificate from that professional that verifies the accuracy of your speedometer. Your odometer must also be accurate within 4 per cent of the actual amount of kilometres travelled. I asked Transport Canada what the standards were for speedometer accuracy. How to test your speedometer There are two ways. I received a ticket for speeding but my speedometer read significantly lower that what the officer told me I was going. In this particular case, let’s say that your speedometer was reading 55 mph. To prevent automated spam submissions leave this field empty. It's my guess they do it this way so they meet both US and UK regulations with one standard. The trouble is that for virtually all of these incidents, I knew how accurate my speed measuring device was but these drivers had no idea whether their speedometer was accurate or not. This makes me wonder, is there a way then to test the accuracy of my speedometer? The basic speed app is free but you can upgrade to get built-in maps and a head-up display. For example, if your speedo says you’re going 100km/h in a car built this year, you will be travelling somewhere between 87.3km/h and 100km/h depending on how your manufacturer programs the speedometer. 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. Which should I trust? If the number is higher than 1.0, your speedometer is reading low and you’re going faster than you think. With the stopwatch or wristwatch, time your vehicle for several miles over a stretch of road at a steady speed (If your car has cruise control, use it). If you are experiencing inaccuracies in relation to your vehicle speedometer, you should contact the original vehicle manufacturer.". This results in quite a different speedometer reading to US vehicles in some cases. If the speedometer reading is higher than the actual speed, the speedometer is fast. Throw in some tire wear, improper tire inflation, a change of tires and wheels or even just a replacement tire of the same size classification and you can change this reading even more. I then did some testing and we found that on average the vehicle was travelling at 6km under the speed on the speedometer, apparently this complies with ADR and is an extra safety feature. At speeds above about 90 km/h the allowable range for speed is 4% of the highest reading shown on the speedometer. Your speedo and your sat nav calculate speed in different ways. 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. Calibrate your speedometer in less than a minute and you don’t even have to leave your driveway! That’s a priority because we don’t know of any police officer that will accept an inaccurate speedometer as a logical excuse for your 100 mph trips down the interstate. 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