Topic: | Re:Re:Is it harder at 20mph? | |
Posted by: | Michael Robinson | |
Date/Time: | 20/01/16 13:16:00 |
"There is also an issue with speedometers being less accurate at lower speeds" Are you sure that is the case? If the speedometer speed is based upon counting revolutions of axle or driveshaft, and translating this into a distance hence speed, then an error in the measurement of one revolution (maybe based upon the assumed diameter of the tyres) will produce a bigger difference between speedo and true speed for higher speeds than lower speeds. The UK regulations say: 2. For all true speeds up to the design speed of the vehicle, the true speed shall not exceed the indicated speed. 3. For all true speeds of between 25 mph and 70 mph (or the maximum speed if lower), the difference between the indicated speed and the true speed shall not exceed— V/10 + 6.25 mph where V is the true speed of the vehicle in mph. So if the speedo says 10mph, or 20mph or 50mph or whatever, the car can't be going faster than this speed. This implies that the true speed will be slower than the speedo as manufacturers will want to have a margin of error, but it can only be slower up to a point as given by the formula, so if the speedo says 25mph, the true speed can't be less than 16.25mph, or if 60mph, can't be less than 47.75mph. |