Drive exactly 60 mph until you reach the next marker while timing it with a clock with a second hand or with a stop watch (best to have a partner do this for safety). She said she was going about 5 MPH and the speedometer was reading 80. John D Wilson from Earth on November 22, 2011: Hi Au fait. You can use nearly any freeway, or limited access expressway, or even a less traveled state or county road. A. 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). 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. How much money can I get for my dead car? Image credit: Pixabay. Your speedometer may or may not show a number. Many drivers have reported this exact phenomenon in recent years, as satnav has become more prevalent in cars, and the situation is actually common to nearly every car on the market. Even when I do speed up, it is nothing close to what my “stationary/road” speedometer measures, and then can be up to 20 km/hr behind; it’s like I … How do I know if my speedo is accurate? Off by 30%. I know that people tend to speed up sometimes when a fast motorcycle is present, but this seems a little faster than normal. Most speedometer from 1965 on use 1000. On the occasions I use my smartphone as a sat nav, I get a readout of the speed of the car on the screen. Which is more accurate, the speed shown on a speedometer or a sat nav? Speedometer gear has twenty teeth. What Does The H And The C Stand For Which Is Located Next To The Speedometer This is hard to explain but i’ll try, i have noticed that there’s a 3 circle next to the speedometer all the way at the right, which has the How Do I Juice Up My Car I am trying to juice up my 95′ Impala SS and I only know a little about cars. To determine your actual speed, you divide the number of minutes it takes you to drive the distance into 60 (the number of minutes in an hour) and then multiply this figure by the distance you traveled. They regulate many things about how our vehicles are constructed and how their systems must function. I don't doubt that these drivers were telling me the truth. Older cars will need a different speedometer drive gear installed in the transmission. I am trying to figure out why is it doing this? So how do you know if your speedometer is accurate? So, gathering a fat mug of coffee for a late-night adventure (which became wee morning hours), I mapped out the plan of A signal originates from a driven gear that meshes with the transmission tail shaft. Gear Driven Speedometer Operation . This makes me wonder, is there a way then to test the accuracy of my speedometer? Your odometer must also be accurate within 4 per cent of the actual amount of kilometres travelled. It's my guess they do it this way so they meet both US and UK regulations with one standard. https://haynes.com/en-us/tips-tutorials/how-check-your-speedometer-accuracy - Car and Driver Magazine. I don't doubt that these drivers were telling me the truth. This app is known to be the best one among all the speedometer apps for iOS. But the accuracy of a speedometer depends on the wheels remaining the same diameter as they were when they rolled off the production line. 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. Manufacturers are guided by a standard set by the Society of Automotive Engineers known as J1226 Electric Speedometer Specification. The transmission is a three speed manual. That your reading of the speedometer was more accurate. At 70mph the difference between the two can be as much as 5mph. The other option is GPS; most receivers will tell you your speed to good accuracy. Speedometer: Aftermarket modifications, such as different tire and wheel sizes or a change in the differential gearing, can cause speedometer inaccuracy. When in my car traffic is often going around 80 mph, but when I am on my bike I tend to go the same speed as traffic or faster. The easy way to test is just by aiming at one of those "your speed is" radar signs. You may be well advised to stick to the number on your speedometer that matches the posted limit. It always shows a slower speed than my speedometer by 3-4mph. 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. In this particular case, let’s say that your speedometer was reading 55 mph. Go to an interstate or any road with mile posts or mile markers. This results in quite a different speedometer reading to US vehicles in some cases. Therefore, 5 minutes and 15 seconds would be 5 + 15/60 minutes, or 5.25 minutes. Whether you have a 1969 Chevrolet Nova Super Sport, a 50s era Oldsmobile Rocket Eighty-Eight, or even a British sports car like a Jaguar E-Type the speedometers basically work the same. 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